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Extension of 018µm standard cmos technology operating range to the microwave and millimetre-wave regime

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O rder N u m b er 9136649
Effects o f different microwave power levels on chem ical, physical
and histological characteristics o f b eef roasts
Lee, Kyunghee Cho, Ph.D.
University of Illinois at Urbana-Champaign, 1991
UMI
300 N. ZeebRd.
Ann Arbor, MI 48106
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EFFECTS OF DIFFERENT MICROWAVE POWER LEVELS
ON CHEMICAL, PHYSICAL AND HISTOLOGICAL CHARACTERISTICS
OF BEEF ROASTS
BY
KYUNGHEECHOLEE
B.S., Ew ha W omans U niversity, 1978
M .Ag., Korea U niversity, 1982
THESIS
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in the Graduate College of the
U niversity o f Illinois at U rbana-C ham paign, 1991
U rbana, Illinois
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U N I V E R S I T Y O F IL L I N O IS A T U R B A N A -C H A M P A IG N
TH E G R A D UA TE COLLEGE
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PHYSICAL AND HISTOLOGICAL CHARACTERISTICS OF BEEF ROASTS
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B E A C C E P T E D IN P A R T I A L F U L F I L L M E N T O F T H E
REOUIREMENTS
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EFFECTS OF DIFFERENT MICROWAVE POWER LEVELS ON CHEMICAL,
PHYSICAL AND HISTOLOGICAL CHARACTERISTICS OF BEEF ROASTS
Kyunghee Cho Lee, Ph.D.
D ivision of Foods and N utrition
U niversity of Illinois at U rbana-C ham paign, 1991
B. Klein, Advisor
The objectives of this study were to determ ine (1) the effects
o f different m eat m asses on m icrow ave oven efficiency, chem ical and
physical characteristics of sem im em branosus beef (SM ) m uscle roasts
cooked by m icrow ave heating, and (2) the effects of m icrow ave
pow er levels and final internal endpoint tem perature on chem ical,
physical and histological characteristics of SM beef m uscle roasts.
The results of power output and efficiency of m icrow ave oven
and load factor tests for water and m eat were presented.
The load
affected the m easured pow er output and oven efficiency.
D ifferent
size meat m asses cooked at different rates, as indicated by
differences in cooking time per kg.
W hen water mass was increased,
the efficiency o f the oven also increased.
However, the efficiency of
the oven was decreased as meat mass was increased at all
m icrow ave pow er levels.
Therefore, actual pow er output w ould vary
for different food items because of differences in specific heat.
B eef roasts (1.5 kg) were cooked to three internal endpoint
tem peratures (60, 70, 80°C) using three different m icrow ave power
levels.
Cooking tim e, standing time, post processing tem perature
rise, m oisture, fat, protein, thiam in, w ater holding capacity, Instron
iii
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m easurem ent, and collagen solubility were determ ined.
M yofibrillar
tissue and collagen tissue were examined with both the light
m icroscope and transm ission electron m icroscope.
The use of variable power for microwave cooking of beef roasts
does not result in m easurably different chem ical or physical
characteristics.
H istological exam ination of the ultrastructure of
m uscle and collagen revealed changes in sarcom ere appearance and
size that were related to internal endpoint tem perature.
Recom m endations for m icrow ave cooking of m eat should take into
account m eat m ass, desired endpoint tem perature and post-cooking
tem p eratu re
rise.
iv
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ACKNOWLEDGEMENT
First of all, I would like to thank my advisor, Dr. Barbara P.
K lein, for her guidance and encouragem ent during my graduate
studies.
1 would also like to thank my com m ittee members, Dr. Floyd
M cKeith, Dr. Peter Bechtel, Dr. Susan Brewer and Dr. Susan Potter for
their helpful discussions.
Special thanks is extended to Carol Cox who
provided a facility for the light m icroscope work at Covenant
H ospital.
I also wish to thank all my fam ily members and friends in the
food and nutrition research lab for their love and support, especially
my husband and two sons.
v
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TA BLE O F CO N TEN TS
C h a p te r
Page
1.
I n t r o d u c t i o n ............................................................................................1
2.
R ev iew
of
L i t e r a t u r e .....................................................................5
P r in c ip le s o f m ic ro w a v e h e a t i n g .................................5
S tu d ie s o f m e a t te n d e r n e s s in
m ic ro w a v e h e a te d m e a t s ................................................1 2
S tr u c tu r e o f m u s c le ............................................................. 17
C o lla g e n a n d e la s tin in m u s c le s ................................ 2 7
E n d o m y s ia l a n d p e r im y s ia l c o lla g e n
29
3.
E ffe c t o f M icro w av e C o o k in g o n th e C h em ical
a n d P h y sic a l C h a r a c te r is tic s o f D iffe re n t R o a s t
M a s s e s .................................................................................. ................3 9
I n t r o d u c t i o n .............................................................................3 9
M a te r ia ls a n d m e th o d s..* ...
.......................3 9
R e s u lts a n d d is c u s s io n
45
4.
E ffe c t o f M icro w av e C o o k in g o n R o a sts
H e a te d
to T h r e e D iffe re n t I n te r n a l T e m p e r a tu r e s w ith
T h r e e D iffe re n t M ic ro w a v e P o w e r L e v e ls ................ 6 7
I n t r o d u c t i o n ................................................................. .......... 6 7
M a te r ia ls a n d m e th o d s .....................................................6 7
R e s u lts a n d d is c u s s io n ...................................................... 6 8
5.
U ltra s tru c tu ra l C hanges o f
B o v in e
S e m im e m b ra n o s u s M u s c le D u r in g M ic ro w a v e
H e a tin g ................................................................................................. 9 4
Introduction
.................................................................... 9 4
M a te r ia ls a n d m e th o d s .....................................................9 4
R e s u lts a n d d is c u s s io n .................................................... 9 8
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6.
U ltr a s tr u c tu r a l C h a n g e s o f C o llag en o f B ovine
S e m im e m b ra n o s u s M u sc le D u rin g M ic ro w a v e
H e a tin g ..............................................................................................1 3 8
I n t r o d u c t i o n ........................................................................ 13 8
M a te r ia ls a n d m e th o d s ................................................ 1 3 8
R e s u lts a n d d is c u s s io n ................... .............................. 1 3 8
7.
S u m m a r y ........................................................................................1 6 9
R e f e r e n c e s .................................................................................... 1 7 5
V ita .....................................................................................................1 86
v ii
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Chapter
1
Introduction
Since the m icrow ave oven was introduced to the consum er
market, sales have greatly increased.
This phenom enon m ight be
explained, in part, by m any consumers experiencing the advantages
of m icrowave cooking, such as convenience and speed.
Numerous
studies show that m ost m icrow ave heated foods are com parable in
quality to conventionally cooked products.
There are many studies concerning eating quality of meat
products prepared conventionally and cooked by m icrow ave heating
that reported sm all, inconsistent differences betw een the two
methods (Baldwin, 1977; Korschgen and Baldwin, 1978; Voris and
Van Duyne, 1979; Drew et al., 1980; Fulton and Davis, 1983).
The use
of m icrow ave heating for m eat is lim ited by consum er concerns that
the final product is less acceptable and tougher than when prepared
c o n v e n tio n a lly .
In early research, m icrow ave ovens did not have the variable
pow er feature or well controlled wave distribution in the oven
cavity.
M icrow ave-cooked m eat, especially less tender m eat cuts,
w hich require long cooking tim es to accom plish tenderizing, showed
low palatability and high cooking losses (M arshall, 1960; Ruyack and
Paul, 1972; Ream et al., 1974).
C urrently, m ost m icrow ave ovens have a variable pow er
feature.
D ifferent rates o f heating can be accom plished by using
variable pow er levels and different loads o f food.
One of the
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difficulties in com parisons among studies is the lack of
standardization of pow er output in m icrow ave ovens.
It is im portant
to know actual power output in the m icrowave oven at each setting,
and how the power output is controlled (i.e. on-off cycling tim es).
A lthough m icrow ave ovens have different variable pow er features
and differ in cooking perform ance, consum ers are not fam iliar with
the variability in power features of m icrow ave ovens and how they
work.
In addition, the efficiency of the m icrowave oven varies with
a load change.
Schiffm ann (1987) suggested that load factor tests to
determ ine the effect of load size in an oven should be done for all
m icrow ave heating studies.
A fter variable pow er feature m icrow ave ovens were
in troduced, several researchers show ed im proved cooking
perform ance using these ovens, especially in meat dishes (V oris and
Van Duyne, 1979; Fulton and Davis, 1983).
In general, it is believed that the changes in tenderness of meat
that occur during heating are related to m yofibrillar and/or
connective tissue fibers.
A lthough there are many studies of the
effects o f conventional heating on meat tenderness as shown by the
ultrastructural changes o f m uscles (e.g. Schm idt and Parrish, 1971;
D avey and G ilbert, 1974), relatively few studies have looked at
m icrow ave heating effects on the structure o f m uscles and
connective tissue.
Changes in m eat ultrastructure during heating at
different heating rates can be observed by histological techniques.
Structural changes in heated m uscle observed with scanning electron
m icroscopy (SEM) have been theorized to be related to m eat
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tenderness.
Hearne et al. (1978a) suggested that an increased
am ount o f fragm entation of the m uscle fibers increased tenderness.
Davis and Gordon (1982) showed that rates o f heat application
affected the am ount of evaporative and drip w ater loss from beef
m uscle, and may, therefore, influence juiciness and tenderness.
It has been reported that collagenous tissue is the m ost
im portant structural com ponent affecting tenderness in "less tender"
beef muscle.
It is known that collagen contributes to background
toughness in m eat.
Som e researchers reported that m icrow ave
cooking increased the solubility of collagen (M cCrae and Paul, 1974;
Zayas and N aew banij, 1986).
If microwave heating increases
collagen solubility, it is desirable to use it for cooking meat,
particularly less tender cuts.
Recom m endations for m icrow ave cooking of m eat should be
based on an understanding o f microwave oven characteristics and
how m eat structural com ponents and palatability are affected by
different m icrow ave heating techniques.
W e need m ore inform ation
about the effect o f variable pow er features on meat cooking, i.e., how
tim e base and pow er level affect characteristics of m eat.
The objectives of this study were:
1. To exam ine the relationship of the actual pow er output and
ten different m icrow ave power levels with a specific tim e
base, and to test the load factor to m easure the efficiency of
the m icrowave oven with different load sizes o f m eat cooked
to an internal tem perature of 70°C.
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2. To compare m oisture, fat, protein, thiamin contents, water
holding capacity, shear and com pression values of four
different m eat masses cooked to an internal tem perature of
70°C with three different pow er levels (40, 60, 100%).
3. To investigate whether the solubility of collagen is affected if
microwave cooking tim e is increased to attain the same
internal tem perature due to the meat mass, and if the
solubility of collagen affects the tenderness of meat.
4. To compare m oisture, fat, protein, thiamin contents, water
holding capacity, shear and com pression values and collagen
solubility of sem im em branosus beef m uscle roasts w eighing
1.5 kg cooked to three different internal tem peratures (60,
70, 80°C) with three different power levels (40, 60, 100%).
5. To investigate the ultrastructural changes of m yofibrillar
tissue o f sem im em branosus beef muscle roasts w eighing 1.5
kg, cooked to three different internal tem peratures (60, 70,
80°C) with three different pow er levels (40, 60, 100%).
6. To investigate the ultrastructural changes of collagen tissue
o f semimembranosus beef m uscle roasts w eighing 1.5 kg,
cooked to three different internal tem peratures (60, 70,
80°C) with three different pow er levels (40, 60, 100%).
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Chapter 2
R ev iew
P rin c ip le s
of
m ic ro w a v e
of
L ite r a tu r e
h e a tin g
M icrowaves are electrom agnetic waves with w avelengths in
the range of 1 mm to 30 cm.
The relationship of frequency (f) and
w avelength (X) is f = C/X, where C = 3 x 108 m/s (speed of
propagation in air).
The unit o f frequency is cycles/sec or hertz (Hz).
M ost ovens are specified with their frequency in m egahertz (MHz).
The energy o f electrom agnetic waves is in the form o f high energy
particles and is transported by the waves from the generator to the
m aterial to be heated.
Two frequencies of special interest are 915
MHz, which has a wavelenghth of 32.8 cm and 2,450 MHz, which has
a wavelength o f 12.2 cm.
These frequencies are approved by the
Federal Com m unications Com m ission for use in m icrow ave ovens.
The m ost im portant part of the oven is the m agnetron, which
plays a role as a frequency converter from 60 Hz to 2,450 MHz or, in
some cases, to 915 MHz (Voss, 1981),
line pow er is 60 Hz.
The frequency o f electricity of
The magnetron has a cylindrical diode with a
metal cathode located in the center, which is electrically heated to
release electrons.
cathode.
The anode circles the circum ference of the
The anode is com posed of resonant cavities that act as
oscillators and generate electric fields.
The m agnetic field is created
by a m agnet that surrounds the m agnetron.
W hen pow er is supplied,
an electron-em itting m aterial at the cathode becom es excited and
em its electrons into the vacuum space between the cathode and
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anode.
The energy o f the electrons gets caught in the fields and
travels as waves through the m agnetron to the antenna.
O scillating
waves are transm itted through the antenna to the w aveguide.
From
the waveguide, waves travel to the oven cavity and are dispersed by
a stirrer, which reduces hot and cold spots in the oven cavity.
K nutson et al. (1987) summarized the events leading to the
developm ent o f the m odern m icrowave oven.
A fter the Raytheon
Company announced the first Radarange in the trade literature in
1946, there were great im provem ents in the m icrow ave oven.
In
1967, the production of countertop m icrow ave ovens was possible.
Early researchers used the term 'electronic heating', but there are
three types of electronic heating com m only encountered: induction
using frequencies o f 960 Hz - 1 MHz, dielectric heating using
frequencies o f 1 - 150 MHz, and m icrowave heating.
During the early 1970s, the first variable pow er microw ave
oven produced by L itton Industries was introduced.
can be produced in two ways.
V ariable power
The first concept is continuous
operation at reduced pow er output.
O 'M eara (1989) called this true
variable power.
This design is found only in expensive, custom -built
research ovens.
The second is variable pow er accom plished by on-
off cycles, som etim es called duty cycles.
M ost m icrow ave ovens sold
on the m arket are m ade with this type of variable power.
The tim e base, a repeating period of tim e for one on-off cycle,
is the key to operation of microwave ovens that have the variable
pow er feature.
to sixty seconds.
Tim e bases o f microwave ovens can differ from one
The majority of ovens have tim e bases with a range
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of 12 seconds to 20 seconds.
A longer time base such as 30 seconds
to 60 seconds is used to enhance defrosting capabilities.
The controls
needed for a very short tim e base are more expensive than those
required for a longer time base, and the pow er supply system is
different for different tim e bases (Gerling, 1987).
Varying the power
output of a m icrow ave oven is not simple because of the electrical
characteristics of the m agnetron and the design of the associated
power supply.
There is no standard tim e base; the selection of an
oven’s tim e base is up to the oven manufacturer.
Even though m icrow ave ovens may have the same percent of
"on" tim e for the m agnetron, different tim e bases can produce quite
different heating effects.
Therefore, the tim e base of a variable
pow er m icrow ave oven needs to be specified for experim ents.
Turpin (1989) m entioned that every m agnetron needs a certain
am ount o f tim e (usually 2-3 seconds) to start delivering pow er once
it is activated.
This time is generally longer if the tube is cold.
M ost ovens equipped with variable pow er have a fixed time
base, and the "on" time is changed to get desirable power output.
However, G erling (1987) showed a system where both the "on" time
and the tim e base are changed as the power level setting is changed
as shown in Table 1.
There is a variation in actual power output from oven to oven,
betw een brands and w ithin brands, even though they have the same
nom inal pow er output.
oven output.
Dungan (1987) evaluated the variance of
The differences between actual output and nom inal
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Table 1.
D ifferent tim e base at each power setting.
S e ttin g
Tim e Base "On" Time P o w e r
(sec)
fsecl
(%)
Med. High
10
7.5
75
Medium
12
6.5
54
Med. Low
18
6.8
33
Low
57
5.7
10
output were 0.29 - 14.4%.
Gerling (1987) explained that the main
difference com es from variations in the component values of the
capacitor and differences in the perform ance characteristics of the
m agnetron.
It is
not surprising
to
observe that the pow er output of a
series of identical models has a range of from 575 to 675 watts with
625 watts as the specified value.
The capacitor has the greatest
effect on variation of pow er output due to m anufacturing processes.
For researchers, it is im portant to know the amount o f pow er
delivered in a given tim e for a particular variable power setting,
sim ilar to the oven tem perature specified in conventional heating.
The oven m anufacturer seldom includes inform ation on tim e base
and "on" time.
There has not yet been established in the U.S. a
standardized technique for m easuring oven power output, although
several have been suggested.
Some researchers suggested a method
to m easure pow er output based on the length of tim e required to
boil water, which is related to the power of the m icrow ave oven
(B uffler, 1988).
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The studies w here variable pow er levels were used show ed the
actual pow er output at different pow er settings and explained
methods of calculating pow er output.
M ost m icrowave ovens used in
these experim ents had a lim ited num ber of pow er settings, such as
three or four, w hile ten levels are common today.
Korschgen et al.
(1976) used tw o ovens, which had actual power outputs of 1054
watts and 492 w atts calculated by w ater load m easurem ent.
They
operated these ovens interm ittently in 3-min intervals for the
m icrow ave -220V (1054 w atts) and in 6-min intervals for the
microwave -115V (492 w atts) to get the variable pow er effect.
Presum ably, this provided approxim ately 500 w atts and 250 w atts
cooking power.
V oris and Van Duyne (1979) calculated the output
with the m ethod described by Van Zante (1959).
H aw rysh et al.
(1979) and D rew et al. (1980) m easured power output by the
method described by Korschgen et al. (1976).
Fulton and Davis
(1983) and K orschgen and Baldw in (1978) calculated the pow er
output based on the procedure by Copson (1975).
The preceding
studies cited the sam e principle for m easuring pow er output based
on water load, but differed in the am ount of w ater heated, tim e for
heating and factor for calculating pow er output.
M oore et al. (1980)
used a ro ast setting w ith a poweT output of approxim ately 422 w atts.
However, they did not explain how they m easured the pow er output.
Starrak (1982) and H ow at et al. (1987) used variable pow er to cook
roasts with three different pow er levels (30, 50 and 100%); how ever
they specified the anticipated pow er output as the percent of
nom inal pow er output.
Schiffm ann (1987) described a m ethod of
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m easuring power output o f the m icrow ave oven by heating 1 L of
distilled water at 20 ± 1°C in a 1 L beaker for 1 min. and applying
the form ula P = 69.8 x AT°C, where P = power in watts, AT is the
tem perature rise in °C.
He also suggested measuring the "load
factor", to determ ine pow er output v/ith masses different from 1 kg.
In order for the food to be heated in a microwave oven, it m ust
have m olecules that have unevenly distributed electrical charges.
W hen these m olecules are exposed to an electrical field, they behave
like tiny magnets, and try to line up with the field.
As the electric
field continues changing m illions of tim es per second, these
m olecular magnets are rapidly m oving in the electrical field.
This
attem pt o f dipolar m olecules of the m edium to align with the
m icrow ave field creates friction am ong food molecules resulting in
the heating of the product as energy is transferred.
The most
im portant m olecule in food w hich has an electrical charge is water.
The w ater molecule is a dipole w ith an uneven distribution of
electrical charges.
Because its positive and negative charges are
arranged asym m etrically, it is very active in a m icrowave field.
Therefore, m icrowave heating is accom plished by energy transfer to
a dipole.
Thus, it is possible to cook effectively in microwave ovens
since m ost foods contain large am ounts of w ater (Schiffm ann, 1975).
O hlsson (1983) show ed that high w ater content m eans high
absorption and a small depth of penetration of the m icrow ave energy
as it is absorbed in the outer portion o f food.
He defined penetration
depth as the depth into the food w here the energy has been reduced
to 37% of the surface energy value.
H arrison (1980) suggested that
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for even heating, the size of roasts should be at least 4 inches thick
and twice as long as they are wide due to the depth to w hich
m icrow aves penetrate.
A bsorption of m icrow ave energy also is
influenced by the dissolved salt concentration and the fat content.
F at and cooking oil have low absorption of m icrow ave energy
com pared to w ater m olecules, but fat heats well due to its specific
heat .
In a conventional oven, energy is added to the food molecules
in the form of heat, by conduction.
In a microwave oven, energy is
added in the form of electrom agnetic radiation.
The variable power
reduces localized overheating since some of the heat is transferred to
cool regions during the "off" time (Turpin, 1989).
H eating by m icrow ave is m ore efficient than conventional
heating because heat is generated in the food and not in the air,
container or oven.
Ohlsson (1983) explained that uneven heating
was due to reflection and concentration o f the m icrow aves.
However
he em phasized that it is im portant to rem em ber that m icrow ave
heating results in m ore uniform tem perature d istrib u tio n w ithin the
food than conventional heating.
M ost researchers have show n that
m icrow ave cooking m ethods save m ore energy than other cooking
m ethods (D ecareau, 1975).
Some food products, such as cake and popcorn, need steam
production, and may need continous heating rather than on and off
heating.
For other products, such as m eat, it may be desirable to
cook in the m icrow ave oven with on and off heating.
M eats are
tender when cooked for a long time at a low tem perature.
With
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continuous m icrow ave heating, the tem perature of the m eat may
becom e excessive and meats may becom e tough.
W e need to im prove know ledge concerning m icrowave heating
of foods to contribute to further im provem ents in the heating
perform ance o f m icrowave ovens.
A wide range of heating rates
occurs in m icrow ave ovens due to different power output.
O'M eara
(1989) showed that the heating rate also depends on the size of the
sa m p le .
W hen m eat is prepared in the microwave oven, post-processing
tem perature rise (PPTR) should be considered to get desirable
products.
heating.
PPTR is the increase in tem perature after microwave
The duration and extent of PPTR can be different with the
size, shape and internal tem perature o f the food.
Standing time can
be described as tim e necessary for com plete cooking after rem oval
from m icrow ave oven.
S tu d ie s
of
m eat
te n d e r n e s s
in
m icro w a v e
h e a te d
m e a ts
Since the m icrow ave was introduced, many studies have been
done to evaluate cooking perform ance.
M ost researchers com pared
their results with cooking perform ance of conventional ovens in
term s o f yield, palatability, and nutritive value.
Early researchers
used full pow er in the m icrow ave oven with different cuts of meat,
different sizes of m eat and different cooking methods.
M arshall (1960) com pared 2.3 kg top round roasts of beef
cooked to an internal tem perature of 80°C in the electronic range
with those cooked in the conventional oven.
They found that roasts
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cooked in the electronic range had higher cooking losses and lower
palatability.
They extended their experim ents to obtain an
acceptable product by variation in cooking method.
They showed
that some variation in cooking m ethods im proved the acceptability of
roasts cooked in the electronic range.
Kylen et al. (1964) com pared the thiamin retention and
palatability of m icrow ave and conventional cooking of tender cuts of
boneless rolled beef rib roasts weighing 1.5 kg.
For microwave
heating, meat was cooked to an internal tem perature of 76°C and for
conventional, m eat was cooked to an internal tem perature of 64°C.
Kylen et al. (1964) did not take PPTR into account, so the microwave
heated meats were cooked to a higher internal tem perature.
Roasts
prepared in the electronic range showed higher cooking losses, lower
m oisture content and thiam in content than those in the conventional
oven, and no difference in fat content.
Also roasts prepared in the
electronic range had significantly low er palatability.
Ream et al.
(1974) com pared the tenderness of large (3.8 kg) and small (1.2 kg)
beef arm and rib roasts cooked in the conventional electric and
m icrow ave ovens.
They showed a wide range (60°C and 71°C,
respectively) o f internal tem peratures of roasts, again due to the
PPTR.
Large arm roasts cooked by microwave vs. conventional
heating showed significant differences in total losses and press fluid.
Total losses and press fluid of roasts cooked in the microwave oven
were higher than those o f roasts cooked in the conventional oven.
H ow ever, shear and sensory characteristics w ere not significantly
different.
Large rib roasts cooked in the m icrow ave oven were
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significantly d ifferent from conventionally cooked in sensory
characteristics and press fluid.
B ut press fluid values for m icrow ave
cooked rib roasts were low er than those of conventionally cooked
meat.
Small arm roasts and small rib roasts cooked in m icrow ave vs.
conventional oven showed great differences (p<0.01) in m ost
characteristics except press fluid.
Small m eat sizes had greater
differences than large sizes.
K orschgen et al. (1976) reported quality factor changes in beef
ribeye roasts cooked to an internal tem perature of 70°C by using two
different pow er level m icrow ave ovens (492 watts vs. 1054 watts).
They sim ulated variable pow er by turning the ovens on and off with
3 min and 6 min intervals.
They showed no difference in cooking
losses between the two m icrow ave energy ieveis.
H owever, when
they w ere com pared with m eat cooked conventionally, cooking losses
w ere significantly greater fo r m icrow ave than for conventionally
cooked beef.
Shear values of interior cores of roasts were not
significantly different.
Shear values of edge cores o f roasts cooked
with 1054 w atts m icrow aves w ere lowest among three cooking
treatm ents.
They stated that patterns in significant differences in
tenderness and juiciness o f beef were not consistent and w ere not
related solely to the m ethod of cookery.
Baldw in (1977) review ed research on m icrow ave cooking of
m eat up to 1977 and noted that there w ere some serious errors and
oversights.
Cooking pow er and frequency were not specified well in
early studies.
Those param eters should be noted to give an idea
about cooking intensity, ju st like know ledge of conventional oven
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tem perature.
She also summ arized those studies and suggested that
the quality o f m eat cooked by m icrowave could com pare favorably
with conventionally cooked meat.
She mentioned that application of
full or high power should be long enough in the initial stage of
cooking to generate sufficient heat in the product to start the cooking
process effectively.
Because moist heat is known to be a good method to increase
tenderness of less tender cuts of m eat, Korschgen and Baldwin
(1978) com pared the eating quality of beef round roasts cooked by
m oist-heat m icrow ave cooking, using high (550 watts) for the first
10 min follow ed by sim m er setting (250 watts), with conventionally
braised m eat cooked to an internal tem perature of 98°C.
C onventionally cooked roasts showed higher sensory scores for
tenderness, and m icrow ave cooked meat showed higher retention of
some nutrients.
There were no significant differences in cooking
losses, m oisture content and sensory scores for flavor and juiciness of
roasts cooked by the two methods.
Hawrysh et al. (1979) investigated the effects of m icrow ave
cooking by using m edium m icrow ave setting and conventional
heating on the cooking losses and eating quality of eye of round
roasts cooked to an internal tem perature of 65°C.
They saw
significant differences in cooking losses, tenderness, texture and
shear values.
Juiciness, softness, flavor, residual connective tissue,
overall acceptability and w ater holding capacity were sim ilar.
V oris and Van Duyne (1979) compared the sensory quality of
top round beef roasts w eighing 1.5 kg cooked by dry-heat
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microwave, using "roast" (about 300 watts) follow ed by "simmer"
setting (about 200 w atts), with roasts cooked by conventional
roasting to an internal tem perature of 68.3°C.
They reported that
there were no significant differences in cooking losses, m oisture
content, shear and press fluid values and sensory scores for
tenderness and juiciness for cooked meat.
Drew et al. (1980) com pared the effects of m icrow ave cooking
o f top round beef roasts cooked to an internal tem perature of 74°C at
different m icrow ave pow er levels (553 watts vs. 237 watts) with
conventional method.
Total cooking losses were highest at the
m icrowave "high" level and lowest with the conventional oven.
But
taste panel evaluations and shear values were not significantly
different among the three cooking m ethods.
M oore et al. (1980) studied the effect of different heat
treatments such as dry or m oist heat in a conventional or a
m icrow ave oven on top round steaks that were cooked to an internal
tem perature of 65°C.
M icrow ave cooked m eat show ed higher
cooking losses, low er m oisture content and low er sensory juiciness
and tenderness scores (PcO.001).
There were no significant
differences in w ater-holding capacity and shear m easurem ent
betw een the tw o cooking treatm ents.
Starrak (1982) m ade three m icrow ave pow er level
com parisons (30, 50 and 100%) using top round roasts weighing
approxim ately 1.5 kg, cooked to an internal tem perature o f 60-65°C.
She mentioned that 1.5 to 1.8 kg with a diam eter of 8.9 to 10.2 cm is
an ideal roast in size and shape for m icrowaving.
She showed that
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when low pow er was used, m ore uniform ity of doneness and low er
cooking losses w ere attained.
She reported a great difference in
cooking losses of roasts cooked with three different power levels.
Fulton and Davis (1983) com pared the eating quality o f beef
ribeye roasts cooked at full pow er for the first 5 min followed by
70% pow er in the m icrow ave oven with roasts cooked conventionally
to an internal tem perature o f 71°C, and top round and chunk roasts
cooked at 50% m icrow ave pow er with roasts braised conventionally
to an internal tem perature of 82°C.
They reported that the yield of
cooked lean m eat was the same for round and chuck roasts cooked
by either cooking m ethod, w hile the yield was lower for the rib eye
roasts cooked in the m icrow ave oven than in the conventional oven.
Sensory scores for tenderness, softness and flavor, and shear values
w ere not affected by the treatm ent.
They stated that m eat prepared
by m icrow aves can result in a product com parable to conventional
oven preparation if proper instructions are followed.
Howat et al. (1987) com pared the palatability of beef blade
roasts cooked by m oist heat m icrow ave cooking at 30% pow er (210
w atts) with conventional cooking.
They showed sim ilar results in
cooking losses, shear and sensory values between m ethods, but
cooking tim e was reduced in m icrow ave heating..
S tr u c tu r e
of
m u sc le
Tenderness is known as the m ost im portant characteristic in
judging m eat palatability.
M any investigators have studied the
effects o f tim e and end point tem perature on m eat tenderness.
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D uring heating, m uscle undergoes progressive physical and chem ical
changes.
It is known that the changes in tenderness o f m eat that
occur during heating are related to m uscle and/or connective tissue
fibers.
The main changes during heating occur in m yofibrillar and
connective tissue proteins, and affect the texture of cooked meat.
Bouton and Harris (1972) believed that m yofibrillar strength
was related to W arner Bratzler shear force values.
The connective
tissue strength was quantified by com pression or adhesion
m easurem ent and juiciness by percent cooking loss.
B outon et al.
(1975) suggested that the tenderness of cooked m eat was a function
of m uscle fiber toughness, connective tissue toughness, and juiciness.
H istological m ethods have been used to observe cooked muscle
structure and its relation to sensory, physical, or chem ical
characteristics of the m uscle.
Several researchers have used electron
m icroscopy (either transm ission or scanning electron m icroscopy:
TEM or SEM) for evaluating the histological changes during heating.
M uscle fiber
Normal m uscle has the follow ing structure (Davis and G ordon, 1982).
Actin, Tropomyosin & Troponin
M-Line
Tropomyosin & Actinin Myosin X
«
Z Disc
¥
I— HZone— I
I Band
Sarcomere
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Factors affecting ultrastructural changes of muscle fibers
T e m p e ra tu re .
Chrystall (1970) observed structural changes of
m uscle fibers at different tem peratures.
W hen m uscle was heated to
55°C, there were no changes in structural elements.
band and Z-lines increased at 70°C.
D ensity of the A
There was still filam ental
organization of the I band at 80°C.
Schm idt and Parrish (1971) observed the effect of different
internal tem peratures and m aturity on the m yofibrillar proteins of
bovine longissim us dorsi (LD) by light, phase-contrast and electron
m icroscopy.
Steaks 3.1 cm in thickness w ere heated to internal
tem peratures of 50, 60, 70, 80, and 90°C.
Electron and phase
contrast m icroscopy showed that m yofibrillar proteins were
com pressed and sarcom eres were shortened at 50°C.
H eating to 60°C
caused loss of M -line structure, initiation of disintegration and
coagulation of thin and thick filam ents and further m yofibrillar
protein shrinkage.
Heating to 70 and 80°C caused more
disintegration o f thin filam ents and coagulation of thick filam ents.
A t 90°C, an am orphous structure resulted, but regardless of the
internal tem perature the principal banding features of the sarcom ere
could be identified.
Davey and G ilbert (1974) identified two distinct toughening
phases in beef sternom andibularis during heating from 25 to 100°C
in w ater bath for 1 h.
A three to fourfold toughening occurred in the
first cooking phase between 40 and 50°C, which was associated with
loss o f myosin solubility, follow ed by a further doubling in the
second phase betw een 65 and 75°C, which was closely associated
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with collagen shrinkage.
During the cooking of m eat at tem peratures
up to 80°, an increase in toughness was observed.
Bouton et al. (1975) measured the sarcom ere lengths o f some
m uscles at different conditions by using the laser method.
They
show ed no significant difference in sarcom ere lengths betw een raw
sam ples and sam ples cooked to 50 or 60°C.
When they com pared the
sarcom ere lengths o f m uscle samples cooked to 60°C vs. 80°C and
m uscles cooked to 60°C vs. 90°C, there were significant differences.
They also observed the changes of sarcomere lengths o f m uscle
samples cooked to 60°C and 90°C for different cooking tim es up to 24
h.
A t 60°C, there were significant differences in sarcom ere lengths of
m uscle as cooking time was increased.
However, at 90°C, not much
difference in sarcom ere lengths of m uscle was observed as cooking
tim e increased.
The ultrastructural changes of two different m uscles heated to
d ifferent internal tem peratures of 60, 70 and 80°C w ere exam ined
with SEM by Cheng and Parrish (1976).
Changes observed in psoas
m ajor (PM) m uscle were different from those in the LD m uscle.
In
PM m uscle, intact m yofibril band tubules were observed in both the
heated and unheated sam ples.
They explained that this m ay be due
to the "loose" packing of myofibrils unique to PM muscle.
F urtherm ore, less shrinkage and coagulation of m yofilam ents in the
A band region and w ider I band regions were noted.
These
observations o f looser packing of m yofibrils, thinner m yofibril
threads and w ider I band regions offered additional evidence as to
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why steaks from PM muscle are more tender than those from LD
m u scle.
Jones et al. (1977) cooked cubes of semitendinosus (ST) muscle
about 1-2 cm on a side for 45 min in parafilm -covered test tubes
suspended in a water bath at 50, 60 and 90°C.
The effects of heat on
morphology were slight at 50°C, but readily apparent at 60 and 90°C.
H eating to higher tem peratures caused fractures to occur
increasingly at fiber surfaces and at Z-lines.
Despite the obvious
deterioration of structure, the overall sarcom ere array rem ained
rem arkably intact, even at 90°C.
Leander (1977) reported that heating to 63°C resulted in
m inim al m yofibrillar degradation for both LD and ST muscle.
Filam ental structures o f actin and myosin could be discerned and
slight shrinkage of sarcom ere length was seen.
There w ere minimal
structure differences of ST m uscle between 63°C and 68°C.
Although
som ew hat decreased in total num ber, actin filam ents in the area of
the I band were still discernible.
However, pronounced differences
in ultrastructure of LD m uscle between 63° and 68°C w ere observed
such that considerable shrinkage of the sarcom ere and an alm ost
com plete loss of characteristic banding features were evident.
Some
filam ental structures could be seen but the overall banding
appearance o f the myofibrils was intact.
Heating to 73°C resulted in
sarcomere lengths of 1.8 pm showing a 9% reduction in the ST
m uscle.
Banding patterns, although somewhat obscured w ere still
visible.
The Z-line appeared more dispersed and exhibited areas of
structural weakness.
LD m uscles heated to 7 3 °C resulted in the
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greatest ultrastructural changes in that Z lines w ere less defined.
Shrinkage in the area o f the A band resulted in a concave appearance
of the sarcom ere showing a 29% rcduc tion of sarcom ere length to
1.17 pm in LD m uscle.
They concluded that the effects of cookery on
the ultrastructure of m uscle varied among m uscles and the most
obvious difference was between bovine ST and LD muscles.
Davis and Gordon (1982) used 600 g bovine ST muscles, which
were cooked in a controlled environment oven at 177°C.
They
reported three relativ ely discrete sarcom ere lengths at subsequent
stages of heating.
W hen significant amounts of the m uscle reached
62°C at T3 (35-62°C), the sarcomere length range was 2.05-2.5 p m .
The sarcom ere length o f the sample at T4 (62-75°C ) ranged between
1.55-2.05 pm .
Based on the differential thermal data, the 2.05 pm
sarcom ere would be related to the denaturation o f m yosin, which
results in the A band region becoming more densely packed and first
sarcom ere shortening.
They concluded that crust form ation and
sarcom ere shortening were critical in m uscle shrink and w ater loss,
even though they m ight not be used as references of tenderness.
Bendali and Resta'li (1983) observed that the changes of the
diam eter and length o f fiber at different internal tem perature of
single m yofibers, sm all m yofiber bundles and m uscle strips from
beef M. psoas and M. sternom andibularis.
They showed that single
m yofibers heated to final tem peratures of 40 to 90°C decreased in
diam eter, but there was no change in length of m yofibers.
However,
m yofiber bundles and m uscle strips below a critical tem perature of
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64°C decreased in diam eter, but above this tem perature, they
shortened rapidly and developed considerable tension.
Cooking m ethod.
Paul et al. (1952) compared the histological
changes of m uscles cooked with two different heat penetrations
(roasting for slow heat penetration, deep fat frying for fast heat
penetration) to 63°C.
The roasted m uscle after storage had a greater
num ber of breaks and areas of granulation, while fried m uscle
showed evidence o f heat rigor, which was revealed by clum ping of
the m uscle substance.
W eidemann et al. (1967) reported the histology of pre-rigor ox
ST m uscle before and after cooking and its relation to tenderness.
M uscle pieces about 10.2 cm. long and 8.04 cm^ cross section were
cooked to an internal tem perature of 85°C in boiling w ater or by
oven roasting, and tenderness was assessed by a tasting panel of
three experienced tasters.
They showed that pre-rigor ST m uscles
were tender if boiled but tough if roasted.
They explained this as
better heat transfer for samples cooked in boiling w ater instead of
roasting.
This im proved the tenderizing effect of cooking
unrestrained pre-rigor m uscle.
Electron m icroscopy show ed that
cooking destroyed many details of the fine structure o f the muscle,
but the general outlines rem ained.
Contraction bands had form ed at
the Z bands and there was little disruption in the sarcomeres.
M -lines were still visible.
The
M ost sarcom eres contracted to the point
w here the Z band ju st touched the ends of the A band filam ents.
They concluded that tenderness in beef m uscle was produced by
disruption of the actin and m yosin filam ents by breaking dow n of
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linkages betw een the actin and myosin filam ents in the sarcom eres,
if the effects of connective tissue were negligible.
Roberts and Law rie (1974) com pared conventional heating
with m icrowave heating on bovine LD muscle cooked to 45 to 90°C
by observing protein denaturation with biochem ical m ethods.
They
showed that m icrow ave cookery caused less physical dam age to both
the connective and m yofibrillar tissues as a consequence of either
high cooking tem perature or shorter cooking tim es being required to
reach the same internal tem perature as by conventional cooking
m e th o d s.
C ia and M arsh (1976) com pared the ultrastructure of pre- and
post-rigor beef sternom andibularis m uscles cooked by m icrow aves
and by boiling.
They show ed that the samples cooked in a
m icrow ave oven were m ore tender than those cooked by boiling, and
in the pre-rigor m uscle, w eight losses for microwave heating were
sm aller.
Pre-rigor m uscles cooked by m icrowaves show ed intense
supercontraction bands separated by less contracted and som etim es
fragm ented areas.
They suggested that the tenderness of m eat
cooked in a pre-rigor state was largely a consequence of a shattering
o f fiber structure in som e areas.
They concluded that fragm entation
and tearing brought about by supercontraction bands played an
im portant role in tenderness.
They also reported the absence of
supercontraction bands in p o st-rigor m uscle.
B outon et al. (1977) reported that com bined pressure and heat
treatm ent did not show the increase in shear force values and
cooking tem peratures over 60°C associated w ith m yofibrillar
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hardening and resulted in breaks in the middle of the sarcom ere of
ST muscles.
The effects of two different heating rates of cooking
were com pared by H eam e et al.'(1 9 7 8 b ).
They investigated
progressive structure changes in heated bovine ST m uscle fibers
using phase contrast microscopy and SEM.
Cores of ST muscle, 2.5 cm
in diam eter, from beef round placed in tubes were heated in a w ater
bath at rates com parable to the oven roasting of the top round roasts
at 93°C and 149°C to end-point temperatures of 40, 50, 60 and 70°C.
Increased heating o f m uscle fibers resulted in the disintegration of Zline structure; increases in interm yofibrillar spaces; shortening of
sarcomeres; cracks and breaks in myofibrils.
The slow rate of
heating resulted in extensive granulation and fragm entation of the
muscle fibers.
The effect of heating rate on the disintegration of
m uscle fibers suggested that the rate of heat penetration m ight
influence the type and extent of disintegration o f m uscle fibers.
H eating to 70°C resulted in extensive fragm entation of m uscle fibers.
H sieh et al. (1980) observed the ultrastructural changes in preand p o st-rig o r beef sternom andibularis m uscle by m icrow ave
cooking and roasting.
The muscle was cut into strips of equal length
and cooked for 1.5 min by microwaves and cooked in boiling w ater
for 8 m in or roasted in an electric oven at 149°C for 12 min to give
an internal tem perature of 70±5°C.
M icrowave cookery produced
sm aller and less dense supercontraction nodes in pre-rigor m uscle
with less tearing and fragm entation but more fiber separation.
A lthough tenderness scores or shear values were not obtained in this
study, the presence o f supercontraction bands in all pre-rigor
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sam ples after cooking supported the concept that developm ent of
heat rigor or supercontraction bands contributes to the greater
tenderness of m eat cooked in the pre-rigor state.
They also reported
that m uscle cooked post-rigor showed no evidence of
supercontraction bands, regardless of cooking m ethod.
Pre-rigor
m uscle cooked w ith m icrow aves resulted in less dam age to the
structure o f the m yofibrillar elem ents than conventional cooking.
Cia
and M arsh (1976) explained that m icrow ave cooked m eat was
heated for shorter tim es and much low er external tem peratures,
probably resulting in less m yofibrillar coagulation.
Hutton et al. (1981) evaluated the changes that occurred in
beef ST muscle heated slow ly in conventional oven and rapidly in a
m icrow ave oven to internal tem peratures of 40, 50, 60 and 70°C by
using SEM.
As end point tem perature increased, there were
concom m itant increases observable in interm yofibrillar spaces, fiber
fragm entation, and occurrence o f nonfibrous connective tissue.
D ifferences in the effects of the oven treatment on the m yofibrillar
structure w ere difficult to observe from the micrographs.
Significant
differences were caused by the end-point tem perature not by oven
treatm ent.
But the difference was observable in the 70°C samples.
They stated that the difference in the oven treatm ents for the
various characteristics occurred between 60 and 70°C.
A t 70°C,
m icrow ave sam ples w ere m ore fragm ented, flattened and coagulated
than the conventional sam ples.
Cham bers et al. (1982) studied the histological characteristics
o f m uscle fibers, connective tissue, and quantity and distribution of
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fat in beef top round steaks cooked by dry or m oist heat in a
conventional or m icrow ave oven, and its relation to sensory
tenderness o f the m uscle.
They reported that effects of the four heat
treatm ent com binations on histological characteristics of bovine
m uscle did not differ significantly and concluded that histological
characteristics of m uscle should not be used extensively to study
relationships betw een m uscle structural com ponents and sensory
tenderness o f the m uscle.
M acfarlane et al. (1986) showed ultrastructural changes of
sheep SM m uscle that was heated to 60°C with com bined pressureheat. They show ed th at pressure-heat treatm ent disrupted Z -line
m aterials, leaving voids at the M -line region.
However, heat treated
m uscle showed intact H-zone and Z-line m aterials.
They suggested
that pressu re-h eat treatm ent gave irreversible disaggregation of the
m yosin o f thick filam ents.
C o lla g e n
and
e la s tin
in
m u scles
V enable (1963) observed that m ost of the elastin in bovine LD
m uscle w as present around blood vessels with some odd elastin
fibers less than 2 p m in diam eter scattered in the perim ysium .
W hen B endall (1967) m easured the elastin content of various
m uscles, sim ilar results were found.
ST and latissim us dorsi muscles
w ere found to have higher elastin content than the other m uscles.
He also found elastin in the LD muscle, which had lower elastin
content, and the ST m uscle, which had higher elastin content.
Small
amounts o f elastin were confined to arterioles in the LD muscle,
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while much of the elastin in the ST muscle was in the form of coarse
fibers of approxim ately 5 jim diameter.
However, when Row e (1986)
investigated the organization of the elastin found in a ST and a LD
bovine m uscle, they found heavy deposits of elastin in both m uscles,
with lots of coarse elastin fibers in the ST and finer elastin fibers in
the LD m uscle, which is different from the results o f V enable (1963)
and B endall (1967).
Gosline and Rosenbloom (1984) showed that the elastic fibers
o f the alveolar wall of dog lung were composed of two
m orphologically distinct protein com ponents, nam ely, the am orphous
fraction or elastin and the m icrofibrillar com ponents, as seen in
electron m icrographs.
The m icrofibrillar com ponents o f elastic fibers
w ere com posed o f small fibrils about 10-12 nm in diam eter, which
w ere located prim arily around the periphery of the elastin, but may
to some extent be interspersed with it.
Elastin was the am orphous
com ponent in the elastic fibers and had a m olecular w eight of
70,000.
E lastin normally occurs in its contracted state but was
capable of extension to about twice its contracted length.
Totland et
al. (1988) show ed the appearance of perim ysial connective tissue of
bovine M. ST muscles which was interm ingled bundles o f collagen
and elastic fibers.
As seen in TEM micrographs, the elastic fibers
fo rm ed an ex ten siv ely cross-linked three-dim ensional netw ork
com prising about 50% of the volume fraction o f the perim ysium .
B endall (1967) showed that connective tissue of ST m uscle contained
37% elastin.
Light et al. (1985) and Totland et al. (1988) found about
50% elastin content in perim ysial connective tissue of this muscle.
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It is not well understood w hether elastic fiber contributes to
meat tenderness.
W hen Bendall (1967) com pared high elastin
m uscle (over 30% elastin content of total connective tissue) and low
elastin muscle (lower than 3% elastin content of total connective
tissue) for tenderness, both m uscles showed sim ilar toughness.
E n d o m y s ia i
and
p e rim y s ia l
c o lla g e n
During heating, denaturation of collagen is expected.
It is
generally known that collagen fibers undergo therm al shrinkage and
further solubilize into gelatin.
Because various m uscles have
different collagen types with differing amounts and types of cross
links, it is likely that collagen will react differently to heating.
The
factor which governs heat-insolubiiity of different collagen fibers is
co v alen t cross-linking.
Structural changes o f endom vsium
Jones et al. (1977) investigated the structural changes of
endom ysiai collagen o f bovine ST muscle heated at 50, 60 and 90°C
w ith SEM.
Endomysiai collagen was unaffected at 50°C and was
separated from the fiber and standing free.
Endom ysiai collagen lost
its fibrous appearance and was congealed into a solid layer at 60°C.
A t 90°C the endomysiai collagen was nonfibrous and congealed to a
significant extent although fibrous areas were occasionally seen.
Bailey et al. (1979) showed that type I collagen was present in
the epim ysium , types I and III collagen were present in the
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perim ysium , and types III, IV, and V collagen were present in the
endom ysium by using im m unofluorescence.
Wu et al. (1985) mentioned that it was likely that collagen
from different tissue locations would react differently to heating,
because different collagen types had different am ounts and types of
cross-linkages.
They com pared the structural changes of
endom ysium of bovine sternom andibularis m uscles at two different
tem peratures (60 and 80°C).
They showed a fibrous network of
endom ysium betw een m yofibers from the cross sections of samples.
G ranular collagen was present in the 60°C heated samples, while
am orphous m asses were observed along the m yofibers of 80°C
cooked sam ples.
Light (1987) showed electron m icrographs of endom ysium of
bovine LD m uscle, which consisted of fine and nonfibrous
appearance, with sm aller diam eter of fibrous collagen in
endom ysium than in perim ysium .
U nder light m icroscopy,
endom ysiai 'ghost' was observed as open tubes with discontinuous
structures possessing a netw ork of reticular fibers on the outer
surface of the tubes.
The tubes can be of different sizes reflecting
the presence in the muscle of fast and slow m uscle fibers.
Bailey and
L ight (1989) m entioned that their SEM study show ed 100 nm
diam eter collagen bundles in the endom ysium , and TEM study
show ed an average diam eter of 50 nm o f endom ysiai fibers, which
do not form bundles o f fibers.
There is not much inform ation about
structural changes in endom ysium during heating.
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R ow e (1989a) investigated the native structure o f the
endom ysiai connective tissue and the sarcolem m a in post-rigor
bovine ST and LD muscles with SEM.
They showed the difference of
characteristics o f tissue betw een unprocessed m uscle and post-rigor
m uscle and explained that post-rigor m uscle had quite large subsarcolem m al gaps and m yofibrils pulled away from the
sarcolem m a/endom ysial tube because of extraction o f sarcoplasm
during m uscle preparation.
They also showed that endom ysium
consists o f a dense feltw ork of collagen fibrils.
Row e (1989b) investigated the effects of heat on
endom ysium /sarcolem m a of bovine ST and LD m uscles by heating
for 1 h at various temperatures (50 to 100°C).
At 50°C, a large part
o f the collagen fibrils form ing endom ysiai feltw ork and perim ysial
feltw ork appeared to be decorated by the deposition of granular
m aterial on them.
This was interpreted as heat denaturation o f
sarcoplasm ic proteins that had leaked out of the m uscle fibers
through the perforated m em branes into the interstitial space.
H ow ever, many others have interpreted the granular or beaded
appearance of collagen fibrils as being the appearance of therm ally
denatured collagen.
The TEM appearance of the endom ysiai collagen
show n in his study after 80°C for 1 h would appear to support the
interpretation o f deposition o f non-collagenous m aterial onto the
collagen fibrils.
They thought that the real appearance o f heat
denatured collagen m ight be seen to be a thickened, unravelled fibril.
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Factors affecting structural changes of perim ysial collagen
T e m p e ra tu re .
Skelton et al. (1963) compared the effect of
degree of doneness on collagenous tissue in beef roasts from LD and
SM m uscles after cooking to three different internal tem peratures of
55, 70 and 85°C.
They showed lower percent collagen nitrogen of
total collagen in cooked samples than in raw samples.
Degree of
doneness did not affect this. The am ount of collagen nitrogen was
greater in SM m uscle than in LD muscle.
The histological study
showed quantities of collagenous connective tissue were greater in
cooked tissue than in raw tissue due to the swollen granular tissue,
but there w ere no consistent differences in the colors of stained
tissue cooked to three degrees of doneness.
Goli et al. (1964) showed increasing thermal shrinkage
tem perature o f connective tissue from near 55°C to 70°C with
advancing age o f the anim als.
M ohr and Bendall (1969) m entioned
that large pieces o f meat began to shrink and extrude fluid rapidly
during stewing as the tem perature rose above 64°C and it was also at
this tem perature that the collagen fibers o f the epi-, peri-, and
endom ysium began to shrink.
Therefore, high tension that develops
during heat shrinkage of collagen is the main cause of extrusion of
fluid from the meat.
Schm idt and Parrish (1971) show ed that connective tissue
fibers increased in size and degree of aggregation with carcass
m aturity.
A lso, the m ore aggregated fibers from 54-60 m onths
m aturity w ere m ore heat resistant than the less aggregated fibers of
veal and 12-20 m onths m aturity.
They observed that endom ysiai
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connective tissue shrinkage was initiated at 50°C and com pleted at
approxim ately 70°C.
Also, perim ysial connective tissue shrinkage
required internal tem peratures of 60°C and higher to observe any
significant fiber changes such as shrinkage and fragm entation.
However, if endom ysiai and perim ysial connective tissue fibers
showed sim ilar degrees of aggregation, they appeared to react
sim ilarly to heat regardless o f m aturity group.
Paul et al. (1973) investigated the extent of solubilization of
collagen when beef ST and biceps femoris muscles strips, whose
dimensions were 2 x 2 x 7
cm, were roasted to different internal
temperatures (58, 67, 75 and 82°C).
There was a highly significant
increase in percent solubilized collagen with increasing internal
tem perature of the meat.
How ever, when these results were
com pared with texture data from shear force and penetrom eter
readings, the differences with shear force averages were not
significant, but the penetrom eter reading decreased with increasing
heat treatment.
They m entioned that these muscles did not become
significantly m ore tender with increased heat in this tem perature
range (58-82°C), but did become m ore dense and compact.
Paul (1975) observed that there was increased tenderness with
increased solubilization o f collagen in braising, but little softening,
despite increased collagen solubility, on roasting.
Cheng and Parrish (1976) show ed that progressive changes
w ith increasing tem perature w ere observed including endom ysiai
sheath sw elling, and collagen fiber disintegration of bovine LD and
PM m uscles.
A t or above 70°C, the endomysiai sheath rem ained
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intact, but sw elling and crim ping of the endom ysiai sheath were
evident.
D egradation o f collagen fibers in the perim ysium was
initiated at 70°C and intense disintegration was observed at 80°C.
Furtherm ore, fragm ents of collagen fibers and aggregation of
granulated m aterials were found mingled in the perim ysial space in
the muscle sample heated to 80°C.
Aggregates o f granulated
m aterials usually were found in the samples heated to an internal
tem perature of 70°C.
Leander (1977) exam ined the therm ally induced
ultrastructural changes in surface and internal m orphology of bovine
ST and LD muscles with the SEM and TEM.
The meat was cut into
steaks (3.8 cm thick x 6.4 cm diameter) and broiled to internal
temperatures o f either 63, 68, or 73°C.
Heating ST steaks to an
internal tem perature of 63°C exhibited only slight evidence of
therm al induced coagulation and initiation o f connective tissue
gelatinization.
From this they suggested that the sm aller connective
tissue fibers were the first affected and the larger fibers w ere only
slightly affected.
A t 68°C, connective tissue sheaths surrounding
individual m uscle fibers had undergone som e degradation and were
more granular in appearance than observed for 63°C heated samples.
At 73°C, endom ysiai covering was still distinguishable w ith the m ost
obvious change being the loss o f distinct fibrous connective tissue.
The coagulated appearance further indicated alm ost com plete
collagen gelatinization.
Jones et al. (1977) reported that collagen of bovine ST muscles
heated to 50°C show ed no consistent evidence of change and collagen
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of 60°C samples did not appear fibrous, and probably had begun to
gelatinize.
At 90°C, collagen was nonfibrous and congealed to a
significant extent.
Carroll et al. (1978) studied the ultrastructural changes of
bovine ST muscle, both raw and heated to 90°C with SEM and TEM.
Heating to 90°C did not alter com pletely the fibrous nature of the
perim ysium connective tissue.
Some native type collagen fibrils
were observed, even after the severe heat treatment.
From the
repeated m icroscopic studies, the shrinkage, gelatinization and
fragm entation of collagen could be detected.
Tem perature definitely
influenced these characteristics of collagen, however, it is difficult to
define the changes of these characteristics at any particular
te m p e r a tu re .
Burson and H unt (1986) isolated intram uscular collagen from
LD and heated it to 70°C for 70 min or 90°C for 140 min to
investigate the influence o f heating on types of collagen.
of collagen solubilized was greater at 90°C than at 70°C.
Percentage
They also
investigated the influence o f heating on type I and III collagen in
m uscle and indicated that heating intram uscular collagen m ainly
solubilized type I collagens.
Im proved tenderness associated with
increased heat solubility o f collagen m ay be m ore closely related to
heat-induced solubilization o f type I than of type III collagen.
Cooking m ethod.
R eid and Harrison (1971) investigated the
effects of four heat treatm ents (deep-fat fried, oven roasted, oven
braised, pressure braised) on histological characteristics of beef SM
m uscle w eighing approxim ately 820g and m easuring 11 x 11.5 x 6.5
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cm which was heated to 70°C.
A panel of three persons used an
ocular m icrom eter to m easure type of connective tissue and quantity
of connective tissue.
D ifferences among heat treatm ents in relative
proportion o f straight and w avy connective tissue were not
significant.
However, there was a significantly larger quantity of
granular tissue in deep-fat fried, pressure braised, and oven braised
samples than that in oven roasted samples.
When Schock et al.
(1970) m easured other characteristics of these sam ples, oven roasted
sam ples had the slow est rate of heat penetration, longest cooking
tim e, and highest m oisture content.
M cCrae and Paul (1974) studied the influence of various types
and rates o f heating on the collagenous connective tissue, as assessed
by the increase in extraction of collagen from the meat sam ples,
which were 6.5 cm length x 2.5 cm thick, cooked to an internal
tem perature of 70°C.
They observed that the rate of heat
penetration alters the solubilization of the collagen less than does the
m anner in w hich the energy is supplied to produce the heating
effect, since there were no significant differences among different
heating rates produced by the three conventional m ethods.
But the
shear force averages w ere not affected by the heating m ethod.
Percent solubilized collagen o f m icrow ave cooked m eat was higher
than the others and m icrow ave and oven broiling gave a product
significantly softer as m easured by the penetrom eter, than the
b raised
meat.
Hsieh et al. (1980) show ed that pre-rigor m uscle cooked w ith
m icrow aves resulted in less dam age to the structure of both the
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connective tissues and the m yofibrillar elem ents than conventional
cooking.
This is in contrast with the results of M cCrae and Paul
(1974), which show ed m icrow ave cookery caused greater hydrolysis
of collagen than conventional cookery.
They pointed out that
solubility and visible collagen dam age are not necessarily the same.
Hutton et al. (1981) investigated the physical changes that
occurred in beef ST muscle heated slowly in a conventional oven and
rapidly in the m icrowave oven to a internal tem perature o f 40, 50,
60 and 70°C.
They showed the connective tissue of the raw state was
very fibrous and loosely packed
collagen in raw tissue.
and 50°C for both ovens.
coagulated.
At 40°C, collagen was sim ilar to the
A significant difference occurred between 40
At 70°C, connective tissue was globular and
Coilagen was affected more in the m icrow ave than in the
conventional oven.
The conventional samples received higher
sensory scores than the m icrow ave heated samples.
Chambers e t al. (1982) com pared four different heat
treatm ents on histological characteristics and sensory properties of
bovine top round muscle.
They observed a small am ount of
collagenous tissue in raw muscle.
With heating, 21-27% o f fibrous
collagenous tissue decreased and granular tissue becam e apparent.
It appeared to be m ore granular in m oist heat treated tissue of
conventionally cooked than in any of the other heat treated tissues.
W u et al. (1985) showed the native structure o f collagen fibers
in the epimysial, perim ysial and endom ysiai tissue with SEM and
indicated alterations in the native structure caused by different
internal tem peratures (60 and 80°C) of bovine sternom andibularis
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muscles.
U ncooked samples had an ordered array o f collagen fibers.
The epim ysium did not show large alterations after cooking;
however, the perim ysium and endom ysium became granular at 60°C,
and gelatinized at 80°C.
This difference may be related to the type of
collagen or degree of cross-linking present in each location.
Zayas and Naebanij (1986) focused on studying the influence of
two heat treatm ents, m icrow ave heating and boiling, on quality
characteristics of m eats, i.e. solubility of collagen and textural
properties.
They showed that the microwave energy solubilized
more collagen from the m eat samples (200g) than did conventional
heat energy.
Also an increase in percent solubilized collagen by
m icrow ave heating and increasing internal tem perature of the
samples was observed.
Some o f the textural properties of meat
heated by m icrow ave heating w ere different from those heated by
boiling.
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Chapter
E ffe ct o f M ic ro w a v e
C o o k in g
C h a r a c te r is tic s
on
3
th e
o f D if fe r e n t
C h e m ic a l a n d
R oast
P h y sic a l
M asses
In tro d u c tio n
T here are m any studies com paring m icrow ave w ith
conventional cooking.
The results from these studies, as cited in
Chapter 2, are not consistent.
Each study used different sizes of
m eat, d ifferen t in tern al tem perature and d ifferen t cooking
treatm ents.
T hese variations may be the cause of the inconsistent
results in the com parisons o f m icrow ave and conventional cooking.
Schiffm ann (1987) em phasized the im portance of the load factor in
using m icrow ave ovens.
Therefore, the purpose of this study was to
investigate any differences in characteristics of d ifferent sizes of
roasts during m icrow ave heating.
A lso, the relationship of collagen
solubilization and textural characteristics was observed because an
increm ent o f collagen solubilization was expected as m asses of m eat
were increased, due to longer cooking time.
M a te r ia ls
and
m e th o d s
M easurem ent o f pow er output and load factor test
The m icrow ave oven that was used in this experim ent was
Amana R adarange M odel RS 458P w ith nom inal pow er of 700 watts.
The size o f the interior of the oven was 3.6 x 10^ cm^ (39.4 cm deep
x 34.3 cm w ide x 26.7 cm high).
Pow er outputs o f the microwave
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oven at different pow er levels were m easured by the m ethod
described by Schiffm ann (1987).
Before m easuring the pow er output
of the microwave oven, the oven was prew arm ed for 1 min with 250
mL of distilled water.
One liter of distilled water at 20±1°C loaded in
a 1 L glass beaker was placed in the center of the oven and heated
for 60 seconds of actual m agnetron on tim e.
Power output was
calculated by applying the form ula P = 69.8 x AT°C.
Power output
was determ ined in five trials.
For the load factor test with w ater in the cold oven
oven was prewarmed for 1 min with 250
state, the
mL of water. For the
prew arm ed oven state, the oven was prew arm ed for 10 m in with 1.5
L o f water.
Then 50, 100, 250, 500, 1000 or 2000 g distilled water
were loaded in the glass beaker and heated for 15, 30 and 60
seconds of actual m agnetron on time.
Each heating rate was
calculated from the increase in tem perature over heating time.
Pow er output
was calculated by applying the form ula P
=Specific
heat o f water
(4.2 KJ/kg,°C)x Wt. x AT / Time, where P
=measured
pow er output expressed in watts, Wt. = the weight of w ater heated,
AT - the iem perature rise of the load and Time = the tim e heated in
sec.
The efficiency o f the oven was calculated by dividing the
m easured pow er output by the nom inal pow er of the oven.
For the load factor test w ith different m eat m asses, the oven
was prewarmed for 1 min with 250 mL of water.
Four different
m eat masses (100, 500, 1000 or 1500 g) were heated to an internal
tem perature of 70°C including post processing tem perature rise
(PPTR).
Heating rates, pow er output and oven efficiency were
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m easured as described above.
W hen power output of the m icrow ave
oven for m eat was calculated, specific heat of meat (3.2 KJ/kg,°C) was
used for calculation, as suggested by Ohlsson (1983).
Preparation of m eat cuts
W hole sem im em branosus (SM) beef m uscles w ere purchased
from M eat Science Laboratory, University of Illinois, Urbana.
muscles were obtained from USDA Choice Grade carcasses.
All
M uscles
were vacuum packed in plastic bags and were frozen in a freezer at
-20°C until needed for testing.
All frozen roasts were thawed in a
refrigerator at 4°C for 3 days until an internal tem perature of 4°C
was reached before cooking.
was removed.
All visible fat and alm ost all epimysium
The whole SM m uscle was cut into four different size
pieces (four-lOOg and one each 500g, lOOOg and l,500g).
Cooking method
Each roast was placed on a rack in the center of a glass roasting
pan.
For small masses of meat, an 11.5 cm diam eter glass baking pan
was used.
For bigger masses o f meat, a 33 x 23 x 5 cm glass roasting
pan was used.
Each roast was cooked uncovered, using three
different power levels in the m icrowave oven (40%: about 256 watts,
60%: about 360 watts and 100%: about 575 watts) until it reached an
internal tem perature of 70°C, including PPTR.
over in the middle o f cooking time.
The roast was turned
The roast was removed from the
oven at a tem perature low er than 70°C, based on estim ations m ade
during prelim inary tests so that the roasts w ould reach the sam e
final internal tem perature.
D ickson Temprobe 500.
Internal tem perature was m easured by a
A ll treatments were replicated three tim es.
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Sam ple
prep aratio n
Chem ical analysis
Raw sam ples were rem oved from each end
of an individual muscle on the day of cooking.
For the cooked roast
samples, tissue rem aining after the rem oval of the cores for
com pression m easurem ent were ground and used for chem ical
d e te rm in a tio n s .
Physical analysis
A fter cooking, 2.5 cm thick slices were taken
and eight 2.5 cm. cores parallel to the muscle fibers were taken from
those slices.
Four cores were used for shear measurement and four
cores were used for com pression m easurem ent.
M oisture, fat and protein determ inations
Percent m oisture, fat and protein w ere determ ined in duplicate
in all samples.
Percent m oisture was determ ined by loss of weight
after samples were dried in an oven at 105°C for 24 h.
Percent fat
w as determ ined after extraction from the m oisture-free sam ples
with repetitive washes o f chloroform :m ethanol (2:1) over a 24 h
period.
Protein content was analyzed by Kjeldahl m ethod (M eloan
and Pom eranz, 1973).
Protein content were calculated from nitrogen
concentration, using a factor o f 6.25.
T h iam in
d eterm in atio n
Thiam in content was determ ined by a m odification of
thiochrom e assay m ethod (Ellefson, 1984).
Thiamin content of
duplicate samples was calculated in mg per lOOg sam ple on the
m oisture- and fat-free basis.
The apparent percent retention of
thiam in was calculated by dividing the thiam in content of cooked
m eat by the thiam in content of raw meat.
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Cooking time, standing time and PPTR
A fter cooking, the cooking tim e was calculated per kg without
including standing time.
in tern al tem perature
Also standing time and PPTR to get final
w ere m easured.
Cooking losses
D rip, evaporation and total cooking losses were determ ined by
w eighing drippings and all roasts before and after cooking.
W ater Holding Capacity
A Carver laboratory press was used to determ ine the water
holding capacity (W HC) based on a m ethod described by M iller and
Harrison (1965).
WHC was determ ined in triplicate in all samples.
Ground m eat sam ples (300mg) on filter paper w ere placed between
plexiglass plates and subjected to 2000 lb. of hydraulic pressure per
in ^ over a 5 min period.
Samples were air dried and the areas of the
m eat and juice were determ ined using a Hi-Pad digitizer.
W HC was
calculated by the form ula,
WHC =
whole juice area - meat area_______ .
whole juice area
Instrum ental tests fo r textural characteristics
Instrum ental tests for textural characteristics were done using
an Instron U niversal testing m achine m odel 1132.
Shear
m easurem ent was conducted using a W arner B ratzler shear
attachment.
A 50 kg load cell was used with cross head and chart
speeds of 20 cm/min.
Four cores (2.5 cm in diam eter) per roast, two
shears per core, w ere sheared by cutting across the fibers with a
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W arner B ratzler shear attachm ent.
Properties of firm ness and
cohesiveness o f shear w ere calculated from the shear-deform ation
curve.
For the com pression m easurem ent, cores were com pressed
twice to 75% of their height using a flat plunger 5.7 cm in diameter.
For lOOg samples, four lOOg samples were cooked at each replication
to get eight cores for shear and com pression measurement.
P roperties of hardness, springiness and cohesiveness of com pression
were evaluated from the resulting 2 bite curve.
Analysis of percent solubilized collagen
M eat samples were treated by the procedure described by
Zayas and Naewbanji (1986).
Three grams of raw meat sam ples
were introduced into 50 ml test tube w ith teflon coated cap and
hydrolyzed by adding 30 ml 6N HC1.
The test tubes were sealed with
teflon tape and hydrolyzed for 12 h at 118°C.
Cooked ground
samples were hom ogenized with 50 ml of distilled water by using
V irtis 45 hom ogenizer.
The samples w ere separated into residue and
supernatant by centrifugation at 4000 rpm for 10 min.
The residue
of cooked samples was hydrolyzed by the same method.
H ydroxyproline from each hydrolyzate was assayed using the
method o f W ossener (1961).
Collagen content was calculated by
m ultiplying the am ount of hydroxyproline by a factor of 7.25.
Solubilized collagen content was calculated from total content of
collagen in the residues of cooked roasts divided by total content of
collagen in raw samples.
44
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Statistical analysis
Data w ere subjected to analysis of variance using Statview
5 1 2 + (Brainpower, Inc., Calabasas, CA) on the M acintosh computer.
W hen F values were significant (p<0.05), mean separation was
determined by F isher PLSD at the 5 % level.
R e s u lts
and
d is c u s s io n
Pow er output m easurem ent o f m icrow ave oven
Table 2 and Figure 1 show the results of pow er output
m easurem ent o f the A m ana m icrow ave oven at ten different pow er
settings.
Table 2.
This m icrow ave oven has a thirteen second time base.
P ow er output at different power levels of m icrow ave oven.
Pow er Level
(%)
100
90
80
70
60
50
40
30
20
10
The
On time
(sec.)
13
12
11
O ff time
(sec.)
On time
(%)
100
0
1
2
P ow er O utput
(watts)
(%)
92.3
8 4 .6
5 7 5 .5 + 3 8 .8
5 3 5 .4 ± 1 7 .4
485.0+12.3
4 3 4 .6 + 3 2 .5
3 6 0 .8 + 1 7 .9
3 2 9 .8 + 2 3 .8
2 5 6 .1 + 3 1 .9
10
9
3
4
8
7
6
5
6
76.9
69.2
61.5
53.9
7
8
46.2
38.5
2 4 0 .6 ± 2 9 .5
2 0 5 .6 + 1 9 .4
9
30.8
1 0 0 .9 + 1 6 .2
5
4
1 0 0 .0
9 0 .0
8 4 .3
7 5 .5
6 2 .7
5 7 .3
5 3 .9
4 1 .8
3 5 .7
17.5
45
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1001
80-
40-
Actual Power Output (%)
Expected Power Output (%)
Magnetron "On" time (%)
200
T
0
Figure 1.
T
20
T
40
60
Power Levels (%)
T
80
100
Actual power output, expected power output and "On" time
percentage over time base at different power leyels.
- 0 .1 5 i
o
<0
Expected Heating Rate (°C/sec.)
Heating Rate (°C/sec.)
C /3
u
O
o 0 . 10 &0
C
•s
cd 0.05*
o
X
0.00
100
Figure 2.
90
80
70 60 50 40
Power Levels (%)
30
20
10
Heating rates at different pow er levels.
46
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expected ten pow er levels are not exactly correlated with the "on"
tim e percentage based on the tim e base, especially at the lower
pow er level settings.
The actual pow er output is lower than the "on"
time percentage at the ten pow er level settings.
The reason for this
m ight be as explained by Turpin (1989), who m entioned that the
m agnetron needs a certain am ount of tim e to deliver power.
2 shows the heating rates at d ifferent pow er settings.
Figure
As expected,
heating rates were decreased at low er pow er levels.
Load factor test o f different w ater masses and m eat masses
Heating rates, power output and efficiency of the oven with
different w ater loads are shown in Tables 3 and 4 and Figures 3 and
4.
The heating rates, power output and efficiency of two different
oven states (cold or prewarm ed) w ere com pared.
Heating rates were
decreased as loads were increased, as m entioned by O 'M eara (1989).
Pow er output and efficiency o f the oven were increased as loads o f
w ater were bigger.
This phenom enon was observed by several
researchers (Schiffm ann, 1987; G erling, 1987).
In the cold oven vs.
prew arm ed oven, cold oven state had higher efficiency, although the
difference was small.
This was also observed by Voss and
G reenw ood-M adsen (1987).
They thought that this difference was
caused by the oven and m agnetron tem perature in the tw o different
oven states and was typical o f m any m icrow ave ovens.
Schiffm ann
(1987) m entioned that the m easurem ent of m icrow ave pow er output
should be done in the prewarm ed oven state.
There is no
explanation why that state of oven should be used.
M any articles
show ing pow er output did not m ention w hether the oven was
47
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prewarm ed.
Schiffm ann (1987) stated that sm aller loads absorb less
of the available m icrow ave energy.
Tests with w ater loads of
different sizes indicated that the m ore water in the m icrow ave oven,
the more efficiently it heats, i.e. more of the available m icrow ave
energy is absorbed.
The results of the load factor test with different m eat masses
are shown in Table 5 and Figures 5 and 6.
decreased with increasing load of meat.
Heating rates were
Also, power output and
efficiency o f the oven were decreased with increasing load of meat.
This phenom enon is different from that seen with water.
Some
reports suggested that the efficiency of the oven is increased as food
items are bigger (Schiffm ann, 1975; Ohlsson, 1983), but they did not
mention what the food item was.
The efficiency at the 40% power
level was higher than at higher pow er levels.
The pow er output of
the m icrow ave oven was m easured based on specific heat o f food
items.
The pow er output would vary for different food item s
because o f the differences in specific heat.
These factors should be
considered for m icrow ave cooking to get desirable final products.
Table o ana Figures 7 ana 8 show the resuits of load factor test
of meat calculated without PPTR.
Power output and efficiency of the
oven w hen PPTR was excluded w ere lower than those w hen PPTR
was included.
48
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Table 3.
Masses
(s )
Load factor test with water in the cold oven.
H eatin g
(sec.)
AT
(°C)
H eatin g
Pow er output E fficiency
ra te (° C /se c '
(w a tts )
(%)
50
15
2 9 .1 6
1 .9 4 4
4 0 5 .3 2
5 7 .9
100
30
3 3 .8 0
1 .1 2 7
4 6 9 .9 6
6 7 .1
250
60
3 3 .6 1
0 .5 6 0
5 8 3 .8
8 3 .4
500
60
18.61
0 .3 1 0
6 4 6 .3 5
9 2 .3 4
1000
60
9 .4 4
0 .1 5 7
6 5 4 .6 9
9 3 .5 3
2000
60
5 .0 0
0 .0 8 3
6 9 2 .2 2
9 8 .8 9
Table 4. Load factor test with w ater in the prewarm ed oven.
M asses
(g)
H eatin g
(sec.)
AT
(°C)
H eatin g
Pow er output E fficiency
ra te (° C /s e c '
(w a tts )
(%)
50
15
2 5 .5 5
1 .7 0 0
3 5 4 .4 5
5 0 .6 4
1 A A
A\J \J
O A
O
u
3 2 .2 2
1 .0 7 4
4 4 7 .8 6
6 3 .9 8
250
60
3 2 .2 2
0 .5 3 7
5 5 9 .8 2
7 9 .9 7
500
60
1 7 .7 7
0 .2 9 6
6 1 7 .1 6
8 8 .1 7
1000
60
1 0 .0 0
0 .1 6 7
6 9 6 .3 9
9 9 .4 8
2000
60
5 .0 0
0 .0 8 3
6 9 2 .2 2
9 8 .8 8
49
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2.01
Cold Oven
Prewarmed Oven
cS
OS
w
O
i. o -
0.5-
NM
0.0
0
500
1000
2000
1500
W ater M asses (g)
Figure 3. Heating rates for tw o different oven conditions with
different loads of water.
1001
W
9Q .
e
>
o
8
80-
o
Cold Oven
70 H
o
£
m
M -C
Prewarmed Oven
60-
0
1000
500
1500
2000
W ater Masses (g)
Figure 4. Efficiency of tw o different oven states with different loads
of water.
50
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Table 5.
Masses
(fi)
Load factor test with meat.
H eatin g
(m in.)
AT
(°C)
H eatin g
Pow er o u tput E fficiency
ra te(°C /sec)
( w a tts )
(%)
with : 00 % pow er
100
1.34
6 9 .0 8
0 .8 6 0
2 9 1 .1 7
4 1 .6 0
500
1 0 .9 2
6 6 .9 3
0 .1 0 2
1 6 8 .3 1
2 4 .0 4
1000
1 7 .3 4
6 3 .2 0
0 .0 6 1
1 8 5 .4 2
2 6 .4 9
1500
3 4 .3 6
6 6 .5 6
0 .0 3 2
1 4 8 .2 7
2 1 .1 8
with ( 0 % power
100
2 .0 5
6 9 .8 3
0 .5 7 0
1 9 2 .1 5
4 5 .7 5
500
1 6 .2 9
6 8 .6 1
0 .0 7 0
1 1 9 .7 5
2 8 .5 1
1000
3 1 .5 4
6 7 .8 5
0 .0 3 6
1 1 8 .1 5
2 8 .1 3
1500
5 0 .9 1
6 4 .0 4
0 .0 2 1
1 0 1 .2 5
2 4 .1 1
with 10 % power
100
2 .9 5
6 6 .8 6
0 .3 7 8
1 2 3 .5 8
4 4 .1 4
500
2 0 .0 1
6 7 .4 9
0 .0 5 6
9 3 .7 4
3 3 .4 8
1000
3 9 .2 6
6 6 .0 0
0 ,0 2 8
8 3 .6 6
2 9 .8 8
1500
6 5 .4 0
6 7 .6 8
0 .0 1 7
7 9 .0 7
2 8 .2 4
51
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1.0 -i
100% Power
8c/i
0.8 -
60% Power
u
40% Power
0 .6 -
~
60
e
0.4-
0 .2 -
0.0
0
1000
500
1500
M eat M asses (g)
Figure. 5.
Heating rates with four different meat masses
at three different m icrow ave power levels.
50-
40% Power
60% Power
| 40
O
<D
Full Power
«4-i 30
>>
o
c
<D
o 20
W
10
0
500
1000
1500
M eat M asses (g)
Figure 6.
Efficiency o f the oven with four different m eat m asses and
three different m icrow ave pow er levels.
52
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Table 6.
Masses
..... (g)
with
Load factor test with meat without including PPTR.
H eatin g
(m in .)
AT
(°Q
H eating
Pow er output E fficiency
ra te (°C /se c '
(w a tts )
(%)
00 % pow er
100
1.34
5 7 .4
0 .7 1 0
2 4 0 .6 0
3 4 .3 7
500
1 0 .9 2
5 1 .2 5
0 .0 7 8
1 2 8 .5 2
1 8 .3 6
1000
1 7 .3 4
5 1 .2 6
0 .0 4 9
1 4 8 .9 4
2 1 .2 8
1500
3 4 .3 6
5 0 .7
0 .0 2 5
1 1 2 .9 4
16.13
with f 0 % power
100
2 .0 5
6 3 .6 7
0 .5 2 0
1 7 5 .2 0
4 1 .7 2
500
1 6 .2 9
5 7 .2 3
0 .0 5 8
9 9 .7 4
2 3 .7 5
1000
3 1 .5 4
5 6 .6 5
0 .0 3 0
9 8 .2 5
2 3 .3 9
1500
5 0 .9 1
5 1 .4 4
0 .0 1 7
8 1 .1 9
19.33
1 1 0 .8 7
3 9 .6 0
with ^0 % power
100
2 .9 5
5 9 .9 8
0 .3 4
500
2 0 .0 1
5 8 .7 1
0 .0 4 9
8 1 .5 7
2 9 .1 3
1000
3 9 .2 6
5 6 .8 6
0 .0 2 4
7 2 .0 8
2 5 .7 4
1500
6 5 .4 0
6 0 .4 0
0 .0 1 5
7 0 .5 6
2 5 .2 0
53
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O.81
40% Power without PPTR
60% power without PPTR
Full Power without PPTR
o
o
w
o
0.6'
0
I
o
0.4-
S
JZ
0.2 -
o
_c
0.0
0
50 0
1000
1500
Meat M asses (g)
Efficiency
of the oven (%)
Figure 7.
H eating rates with four different meat masses
at three different power levels w ithout PPTR.
•
•
40% Power without PPTR
60% Power without PPTR
•
Fuii Power without PPTR
40-
30-
0
1000
500
1500
Meat M asses (g)
Figure 8.
Efficiency o f the oven with four different meat masses with
three differen t m icrowave pow er levels w ithout PPTR.
54
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Cooking time, standing tim e and PPTR
Final internal tem perature, cooking time, standing tim e and
PPTR of m eat are shown in Table 7.
was reached after standing time.
70°C.
The final internal tem perature
The goal was to cook all roasts to
Cooking time was calculated as min per kg w ithout including
standing tim e.
There w ere significant differences in cooking times
among different pow er levels.
As expected, cooking tim e for full
pow er level is shorter than that for reduced power.
F or the 40%
pow er level, the cooking tim e was significantly different among four
different m eat m asses.
This suggests that when reduced pow er is
used, the cooking tim e should be considered carefully, depending on
the meat m asses so as not to overcook.
As sizes of roast are
increased, the cooking tim es are increased.
It takes longer for a
larger mass o f m eat to heat to a given temperature.
M ost recipes
presenting the cooking tim e for roasting mention the tim e per unit of
weight.
If cooking tim e for roasting beef is affected by load, more
careful recom m endation of cooking tim e is required.
Standing tim e, w hich is the time between rem oval of the food
from the oven until it finishes cooking, does not differ significantly
among three different pow er levels.
However, there are significant
differences in standing tim e due to different m eat m asses except at
100% pow er levels.
W hen total cooking tim e is considered as the
cooking tim e plus standing time, for the larger sizes, longer cooking
tim e (m in/kg) is required.
There are som e differences in PPTR among m icrow ave power
levels.
The higher the pow er level used, PPTR is higher.
Kylen et al.
55
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Table 7.
Final internal temperature, cooking time, standing time
and PPTR of different meat masses with three different
microwave power levels.
Power level
60%
40%
Characteristics
SF
100%
F in al
in te r n a l
temp (°C)
lOOg
500g
lOOOg
1500g
SF
7 0 .8 6 + 0 .4 4
7 1 .4 9 ± 1 .13
7 0 .0 0 ± 0 .3 2
7 1 .6 8 ± 2 .5 3
ns
7 3 .8 3 + 1 .5 9
7 2 .6 1 ± 1 .3 1
7 1 .8 5 ± 2 .2 0
6 8 .0 4 ± 2 .5 1
ns
7 3 .0 8 a
7 0 .9 3 + 1 .5 9
6 7 .2 0 + 0 .6 5
7 0 .5 6 + 2 .6 3
ns
ns
ns
ns
ns
Cooking
tim e
(m in /K g )
lOOg
500g
lOOOg
1500g
SF
2 8 .9 0 + 0 .H A a
3 8 .3 8 ± 0 .0 2 B a
42.07± 0.70B C a
4 5 .6 5 ± 2 .1 3 C a
***
1 9 .3 8 + 0 .0 2 A b
3 0 .4 4 ± 1 .1 3 B b
3 0 .7 5 + 0 .8 7 B b
3 3 .7 9 + 3 .8 5 B b
*
1 3 .2 2 a c
2 1 .2 0 + 2 .72c
1 8 .7 5 ± 0 .4 2 c
2 3 .9 4 + 0 .7 8 c
ns
*
*
*
*
Standing
tim e (m in)
lOOg
1.5 1 + 0.25A
9.67+1.20AB
500g
lOOOg 1 1 .6 7 + 0 .88B
1 5 0 0 g 12.67±5.21B
*
SF
1 .7 2 + 1 .0 5 A
2 .5 0 a
7.00+ 0.58A B 1 4 .3 3 + 4 .8 4
1 1.67± 2.40B 1 5 .3 3 ± 2 .3 3
17.50+ 4.41B 1 6 .0 0 ± 2 .5 2
*
ns
lOOg
500g
<AAA .
lUUUg
15 OOg
SF
6 .1 6 ± 3 .5 4
1 1 .3 8 ± 1 .4 6 a
t -1 AA. A A^
1 1 .ZU£Z.9 o
1 2 .6 0 + 0 .2 8 a
ns
PPTR
(°C)
6 .8 8 ± 0 .5 8
8 .7 8 + 0 .6 7 a
A -i A, r\ AA
^ .i4 + u .^ y
7 .2 8 + 2 .2 6 a
ns
ns
ns
ns
ns
1 1 .4 8 a
ns
15.68±1.68b *
1 * s\ a , r\ a a
1 i .y ^ + u .j /
ns
*
15 .8 6 + 1 .31b
ns
SF: Significance o f F value, significant at 0.05 (*), 0.01(**) or 0.001
(***) level, ns: not significant,
a : This figure represents only one replication.
Small letters show significant differences by different pow er levels.
Capital letters show significant differences by different m eat masses.
56
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(1964) reported cooking tim e o f 34.6 min/kg and 20+0.5 min of
standing time for roasts w eighing 1.5 kg and 10.5°C of PPTR to reach
an internal tem perature o f 74.4°C.
Korschgen e t ai. (1976) reported
13 + 1 min./kg o f cooking tim e, 53+11 min of total preparation time
and 25°C of PPTR of roasts of 1 kg cooked with 1054 watts of
m icrow ave pow er and 26+3 min/kg of cooking time and 54±4
m in/kg of total cooking tim e and 15°C of PPTR of roasts of 1 kg
cooked with 492 watts o f m icrow ave power.
Starrak (1982)
suggested that the cooking tim e of beef top round roast at 650 watts
is 19.87 m in/kg and at 325 watts is 26.49 min/kg and at 200watts is
44.15 min/kg to reach an internal tem perature of 64°C.
She also
m entioned that PPTR depends upon the pow er at which the meat
was cooked.
She showed, in general, roasts rose 8.3 to 11.1°C when
cooked on high; about 5.6°C on medium and 2.8°C on low power
setting.
In this study, no significant difference was seen among
pow er levels, even though there is a trend of increasing PPTR as
p o w er increased.
Cooking losses
Table 8 shows total losses, drip losses and evaporation losses of
roasts.
There are no differences in total losses of four different m eat
m asses cooked w ith three different power levels.
This result is
consistent with Korschgen et al. (1976) and Drew et al. (1980) who
com pared different m icrow ave pow er levels.
H owever, Starrak
(1982) showed significant differences in total losses am ong three
different microwave pow er levels.
Ream et al. (1974) showed
significant differences in cooking losses on two different sizes of
57
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Table 8.
Total losses, drip losses and evaporation losses of four
different meat masses with three different microwave
power levels.
Characteristics
Total losses 1 0 0 g
(%)
500g
lOOOg
1500g
SF
Drip losses
(%)
lOOg
500g
lOOOg
1500g
SF
Evaporation
losses (%)
Power level
60%
40%
3 0 .6 6 + 1 .3 2
3 0 .6 7 ± 0 .2 5
3 2 .9 3 ± 0 .8 5
3 3 .2 1 + 2 .0 8
2 8 .4 7 + 0 .3 5
3 5 .1 6 + 0 .9 8
3 4 .1 0 ± 2 .2 1
3 3 .3 9 ± 0 .7 7
ns
ns
100%
SF
2 6 .9 a
3 5 .5 7 + 1 .5 1
3 4 .1 2 + 2 .3 7
3 4 .0 6 ± 1 .6 0
ns
ns
ns
ns
ns
1 8 .8 1 ± 0 .0 9 A 1 7 .8 9 ± 0 .8 0 A 1 6 .6 0 a
ns
12.0 3 ± 0 .8 2B 13.80±0.74B 1 1 .7 5 + 2 .82A n s
11 .9 2 + 1 .91B 12.66± 0.84B 11.37 + 1.71A n s
1 0 .2 1 + 2 .09aB
8.64+0.40abC 5.77±0.54bB *
*
***
*
lOOg
500g
lOOOg
1500g
1 1 .8 6 ± 1 ,2 3 A
1 8 .6 4 ± 0 .6 1B
2 1 .0 1 + 0 .31C
2 2 .9 9 + 1 .00C
1 0 .5 8 ± 0 .4 6 A
2 1 .3 6 + 0 .91B
2 1 .4 4 + 1 .31B
21.61± 1.15B
1 0 .43a
2 3 .8 4 ± 4 .3 5 A
2 2 .4 2 + 0 .39A
2 8 .2 9 ± 1 .9 3 B
SF
***
:fc
*
ns
ns
ns
ns
SF: Significance of F value, significant at 0.05 (*), 0.01(**) or 0.001
(***) level, ns: not significant.
a : This figure represents only one replication.
Small letters show sig n ifican t differences by different pow er levels.
Capital letters show significant differences by different m eat masses.
58
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roast, showing decreased cooking losses with increasing sizes of meat.
T here are no significant differences in drip and evaporation
losses am ong the three m icrowave pow er levels, except in roasts
w eighing 1.5 kg.
The drip losses of 1.5 kg roasts decreased when
pow er level was increased, as shown by Korschgen et al. (1976).
This
is probably due to the browned surface o f roast caused by longer
cooking tim e preventing further drip losses.
The results showed
significant differences in drip losses and evaporation losses by
different sizes.
In general drip losses w ere decreased with larger
m eat m asses and evaporation losses w ere increased with increasing
m eat m asses, because of evaporation and/or spattering of drippings
during the longer cooking time.
M oisture, fat, protein and w ater holding capacity
M oisture, fat, protein, and w ater holding capacity are presented
in Table 9.
There are no differences in m oisture content and protein
content of cooked roasts among three m icrow ave power levels and
four different m asses.
Fat content had some difference by pow er
level and by meat masses.
The results show a significant increm ent
in fat content by increasing the meat masses.
The difference in fat
content by m eat masses can be caused by sampling in which larger
roasts have m ore interm uscular fat.
The difference of fat content in
m eat cooked at different pow er levels is probably due to the
difference in fat content of raw samples.
Kylen et al. (1964) showed
that the percentage o f m oisture was significantly lower in the
electronic than in conventionally cooked product and fat content was
59
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the same after both methods of cooking.
Korschgen and Baldwin
(1978) and Voris and Van Duyne (1979) reported sim ilar m oisture,
protein and fat contents o f m eat cooked by m icrowaves and
c o n v e n tio n a lly .
There is no difference in w ater holding capacity by different
power levels and m eat masses.
Ream et al. (1974), Hawrysh et al.
(1979) and M oore et al. (1980) com pared the w ater holding capacity
of m icrow ave cooked m eat with conventionally cooked meat.
They
showed no significant difference in w ater holding capacity between
two cooking m ethods.
Thiam in content and thiam in retention
Table 10 shows thiam in content and retention of the meat
samples.
Thiam in content and retention of meat samples do not
show significant differences by the different masses and pow er
levels.
Thom as et al. (1949) reported less retention of thiam in in
beef roasts cooked in an electronic range (63%) than in those cooked
in a conventional oven (75%).
Dawson et al. (1959) reported that the
thiam in retention o f top rounds of beef conventionally braised was
31% to 69%.
Kylen et al. (1964) showed significant differences in
mean percent retention of thiam in in meat cooked by two different
cooking m ethods.
M icrow ave cooked m eat retained 58-67% and
conventionally cooked m eat retained 80-86% of thiam in, but final
internal tem peratures differed.
Korschgen et al. (1976) reported no
differences in thiam in losses at two different m icrow ave pow er
levels but K orschgen and Baldwin (1978) showed significant
differences in the retention o f thiam in of meats cooked by
60
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m icrow aves and conventionally, when the roasts were cooked to an
internal tem perature of 98°C.
They showed that m icrow ave cooked
m eat retained higher thiam in (25% vs. 19%) than m eat cooked
conventionally.
Their explanation was that since there was longer
heating and more browning in the conventional oven, there was
more destruction of thiamin.
Voris and Van Duyne (1979) showed
no significant differences in thiam in retention due to cooking
methods.
It seems that the destruction of thiam in is related to
tem perature, and not to heating rates.
Shear and com pression m easurem ent
Table 11 shows the shear and com pression m easurem ent of
different meat m asses at three different m icrow ave pow er levels.
Shear cohesiveness, which is also called "shear value" in most
reports, shows some inconsistent trend am ong three different power
levels.
Shear cohesiveness and firm ness values o f m eat cooked at
full pow er are low and 60 % pow er shows highest for all meat
m asses.
There are no differences in shear cohesiveness and firmness
due to mass differences except at 60% power.
Voris and Van Duyne
(1979), Fulton and D avis (1983) and Howat et al. (1987) showed no
differences in peak shear force in m eat with two different methods
of cooking.
Korschgen et al. (1976) and Drew et al. (1980), who used
different power levels, did not show any significant differences in
shear values. Only Korschgen and Baldwin (1978) and Hawrysh et al.
(1979) showed significant differences in shear values o f roasts
cooked with m icrow aves and conventional cooking m ethod.
Shear
firm ness shows the sam e trend as shear cohesiveness.
61
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Table 9. Moisture, protein, fat and water holding capacity of four
different meat masses with three different microwave
power levels.
Characteristics
M oisture
(%)
Protein
(%)
Fat (%)
WHC
Power level
60%
100%
SF
7 4 .2 4 + 0 .0 7
7 4 .9 2 + 0 .3 7
7 3 .4 ± 0 .6 8
ns
6 2 .7 3 ± 0 .4 7
6 3 .7 3 + 0 .2 4
6 1 .8 3 + 0 .0 4
6 2 .8 3 ± 0 .4 7
ns
6 4 .0 1 ± 0 .2 2
6 3 .1 1 + 0 .9 5
6 2 .4 4 + 1 .0 5
6 2 .8 4 ± 0 .7 8
ns
6 4 .9 0 a
6 3 .9 1 ± 1 .1 4
6 3 .0 7 + 0 .8 7
6 2 .3 4 ± 1 .9 9
ns
ns
ns
ns
ns
2 3 .6 6 + 0 .3 1
2 3 .4 9 + 0 .6 6
2 2 .6 7 + 1 .6 1
ns
3 4 .4 4 + 0 .9 1
3 5 .4 6 + 0 .5 6
3 4 .9 7 + 1 .4 1
3 2 .3 0 ± 1 .0 5
ns
3 3 .2 6 + 0 .3 6
3 3 .8 7 + 1 .5 3
3 2 .6 7 + 1 .8 1
3 3 .8 4 + 1 .4 7
ns
3 3 .8 4 a
3 3 .0 8 + 1 .6 8
3 1 .8 5 ± 0 .7 5
3 3 .2 7 + 1 .2 5
ns
ns
ns
ns
ns
1 .8 2 ± 0 .2 6
1.5 7 + 0 .3 6
2 .0 4 ± 0 .3 8
ns
40%
ra w
100g
500g
1 OOOg
1500g
SF
raw
lOOg
5QQg
lOOOg
1500g
SF
raw
lOOg
500g
lOOOg
1500g
SF
3 .7 4 + 0 .03A
2 .2 5 ± 0 .1 1A
3.1 l+0.26bA B 1.86+ 0.12aA
4.60+0.63BC 3.5Q±0.49B
5 .43+ 0.55bC 3 .6 2 + 0 .86aB
***
**
2 .3 2 a A
3 .3 7 + 0 .7 9 b A
4.22±0.94B
5 .8 8 ± 0 .8 8 b B
*
ns
**
lOOg
500g
lOOOg
1500g
SF
0.7 7 + 0 .0 1
0 .7 4 + 0 .0 2
0 .7 5 + 0 .0 0
0 .7 6 ± 0 .0 0
ns
0 .7 9 «
0.76+ 0.00
0.75+ 0.00
0 .7 5 ± 0 .0 1
ns
ns
ns
ns
ns
0.78+ 0.01
0.78+ 0.01
0 .7 5 + 0 .0 0
0 .75+ 0.01
ns
ns
**
SF: Significance of F value, significant at 0.05 (*), 0.01(**) or 0.001
(***) level, ns: not significant.
a : This figure represents only one replication.
Sm all letters show significant differences by different pow er levels.
C apital letters show significant differences by differen t m eat masses.
62
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Table 10.
Thiamin content and thiamin retention in four different
sizes of meat masses with three different microwave
power levels.
40%
Power level
60%
100%
SF
ra w
0.150±0.0Q 1
0 .1 5 1 + 0 .0 0 1
0 .1 4 3 + 0 .0 0 3
ns
lOOg
500g
lOOOg
15 0 0 g
SF
0 .1 4 4 + 0 .0 0 5
0 .1 3 7 + 0 .0 0 5
0 .1 3 1 + 0 .0 0 6
0 .1 2 9 ± 0 .0 0 6
ns
0 .1 4 4 ± 0 .0 0 5
0 .1 3 2 ± 0 .0 0 7
0 .1 2 9 ± 0 .0 0 8
0 .1 3 1 + 0 .0 0 1
ns
0 .1 19a
0 .1 1 7 + 0 .0 0 7
0 .1 2 0 + 0 .0 0 3
0 .1 2 2 + 0 .0 0 3
ns
ns
ns
ns
ns
ra w
0 .6 2 8 ± 0 .0 0 7
0 .6 5 3 + 0 .0 4 0
0 .5 8 3 ± 0 .0 3 1
ns
lOOg
500g
1 OOOg
1500g
SF
0 .4 2 8 + 0 .0 1 0
0 .4 1 2 + 0 .0 1 5
0 .3 9 2 + 0 .0 2 2
0 .4 0 5 + 0 .0 2
ns
0 .4 2 7 + 0 .0 1 9
0 .3 7 9 ± 0 .0 3 1
0 .3 7 9 + 0 .0 1 2
0 .3 9 1 ± 0 .0 1 3
ns
0 .3 6 3 “
0 .3 6 2 ± 0 .0 4 6
0 .3 6 7 + 0 .0 1 0
0 .3 8 6 + 0 .0 2 0
ns
ns
ns
ns
ns
lOOg
500g
lOOOg
1500g
SF
6 8 .8 6 ± 1 .7 8
6 5 .5 8 + 1 .7 1
6 2 .2 7 + 2 .7 8
6 4 .4 8 + 2 .8 7
ns
6 1 .7 4 + 4 .0 4
5 8 .2 6 ± 5 .0 0
5 8 .3 1 ± 3 .2 6
6 0 .4 5 + 4 .9 3
ns
6 2 .3 7 “
6 1 ,7 6 ± 5 .0 2
6 3 .4 2 + 4 .8 6
6 6 .3 4 + 1 .4 9
ns
ns
ns
ns
ns
Characteristics
Thiam ina
(mg/100g)
Thiam in^
(mg/lOOg)
Thiamin
Retention
(%)
a; W et basis. &'• M oisture and F at free basis
SF: Significance of F value, significant at 0.05 (*), 0.01(**) or 0.001
(***) level, ns: not significant.
“ '• This figure represents only one replication.
63
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Table 11. Shear and compression measurement of different meat
masses at three different microwave power levels.
Characteristics
Power level
60%
40%
S h ear.
lOOg
9 .86 ± 1 .1 8ab 11.06± 0.26bBC
C o h e siv e ­ 5Q0g
9.65+ 0.79a 14.87+ 3.07bC
ness (Kg) lOOOg 1 1 .0 5 ± 0 .8 1 a
8.48±0.93bA
1500g
9.94+1.2 8 a b 10.74± 1.42bA B
**
SF
ns
S hear
F irm n e s s
(K g /m in )
100%
8 .3 5 a a
7 .7 0 + 0 .6 7 a
8 .5 9 + 0 .36 b
8.1 l± 0 .7 8 a
ns
lOOg 7 2 .1 5 + 1 1 .2 4 a b 8 3 .2 5 + 7 .7 8 a A
5 4 .2 1 a b
5 0 0 g 8 6 .2 6 ± 1 3 .4 5 b l2 9 .3 6 + 2 7 .6 1 ab B 66.1 l± 1 0 .6 8 a
lOOOg 9 0 .3 8 + 1 3 .7 8 b 78.91 ± 6 .4 7 ab A 69.66±8.09a
1 5 0 0 g 84.03+6.39ab 101.06+13.44bA 68.89+9.55a
**
SF
ns
ns
Com pression
lOOg
4 4 .8 3
ND
H a rd n e s s
5 0 0 g 3 3 .9 3 + 5 .4 8 a 3 0 .3 6 ± 2 .3 8 a b
29.13+2.65b
3
6
.0
5
+
2
.3
9
b
(Kg)
lOOOg
3 6 .5 0 ± 3 .6 3 a b
32.16+2.70a
1 5 0 0 g 3 7 .6 7 + 3 .9 7 a 3 6 .2 3 ± 3 .2 8 a b
30.79±3.09b
SF
ns
ns
ns
C o m p ressio n lO O g 0 .0 3 3
ND
ND
Springiness 5 0 0 g 0 .0 2 8 ± 0 .0 0 4 a 0 .0 2 7 + 0 .0 0 1 a
0.037±0.00b
(m in )
lOOOg 0 .0 2 7 ± 0 .0 0 1 a 0 .0 3 2 + 0 .0 0 1 b
0.033+0.00b
1 5 0 0 g 0 .0 2 9 + 0 .0 0 1 a 0 .0 3 2 + 0 .0 0 5 a b 0.036±0.00b
SF
ns
ns
ns
C o m p ressio n lO O g
ND
0 .3 9
C o h esiv e- 5 0 0 g 0.37± 0.Q 76
0 .4 4 ± 0 .0 6 5
0.34+0.056
A OA . A A-1 n
11 uAAA
U'vOO
u u g~ U.O^IU.UJO
0 .3 5 ± 0 .0 2 6
0.43±0.035
1 5 0 0 g 0 .3 4 + 0 .0 2 3
0 .3 3 ± 0 .0 2 9
0.37+0.066
SF
ns
ns
ns
th
a
o
p
SF
*
***
ns
*
*
ns
**
ND
*
*
*
*
*
♦
ND
ns
ns
ns
SF: Significance o f F value, significant at 0.05 (*), 0.01(**) or 0.001
(***) level, ns: not significant. ND : not determined.
a : This figure represents only one replication.
Small letters show significant differences by different power levels.
Capital letters show significant differences by different m eat masses.
64
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There are significant differences in com pression hardness and
springiness at the different pow er levels.
The values of com pression
hardness of roasts cooked at full pow er level are lower than those of
reduced pow er levels and the values for com pression springiness of
roasts cooked at full power level are higher than those of reduced
pow er levels.
The values o f com pression cohesiveness by the
different pow er levels and by different m asses are not significantly
different.
There is no reference show ing com pression values of
m icrow ave cooked meat.
Low er values of shear cohesiveness and
com pression hardness o f m eat cooked w ith 100% m icrow ave pow er
level than with low er power levels m ight be caused by the effect of
intense m icrow aves on m eat, giving m ore structural dam age in
m uscle and collagen fibers.
Percent solubilized collagen
Table 12 shows the percentage of solubilized collagen of
different m eat m asses cooked w ith three different m icrow ave pow er
levels.
Percentage of collagen solubility shows great variation among
replications and no significant difference is seen among different
m eat m asses.
However, there is an increasing trend in collagen
solubility as m eat mass increases.
The correlation coefficients betw een collagen solubility and
Instron m easurem ent are shown in T able 13.
There is no correlation
betw een Instron tenderness m easurem ents and collagen solubility
(p>0.05).
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Table 12.
Percentage of solubilized collagen of four different meat
masses cooked with three different microwave power
levels.
TREATMENT
40%
60%
100%
SF
100g
500g
lOOOg
1500g
SF
1 4 .0 2 ± 4 .4 3 a l6 .4 4 ± 2 .3 5 a b l7 .7 3 ± 1 .8 4 a b 27.12±3.59b
ND
1 6 .4 3 a
*
ND
1 8 .7 9 ± 2 .4 8
24.59± 1.88
1 0 .4 8 ± 0 .3 5 a
2 4 .8 6 ± 1 .1 5 b
26.85±0.89b *
ns
ns
ns
ns
ns
SF: Significance of F value: significant at .05 (*) level,
sig n ifican t.
ns: not
a '• This figure represents only one replication.
ND: not determined.
Table 13.
Correlation of collagen solubility and Instron measurem ent
of different meat masses
Collagen solubility
SC
SF
CH
CS
CC
0 .0 8 4
0 .2 9
-0 .0 6 6
0 .1 3
-0 .0 5
SC: shear cohesiveness SF: shear firmness. CH: compression hardness.
CS: com pression springiness. CC: compression cohesiveness.
66
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Chapter 4
E ffe ct o f M icro w av e C o o k in g on R o a sts H eated
D if fe r e n t
I n te r n a l
T e m p e r a tu r e s
M ic ro w a v e
w ith
Pow er
T h re e
to T h re e
D iffe re n t
L e v els
In tro d u c tio n
There are many studies showing differences in characteristics
o f roasts betw een two different cooking m ethods, microwave and
conventional heating.
H ow ever, there is no inform ation regarding
the characteristics o f roasts cooked to different internal
tem peratures with m icrow ave heating.
The purpose of this project
was to observe the characteristics of beef roasts cooked to three
d ifferen t internal tem peratures w ith three d ifferent m icrow ave
pow er levels.
M a te r ia ls
and
m e th o d s
Preparation o f m eat cuts
Fifteen whole sem im em branosus (SM ) b eef m uscles were
purchased from M eat Science Laboratory, U niversity of Illinois,
Urbana.
carcasses.
All muscles were obtained from USDA Choice Grade
Muscles were cut into about 2 kg, vacuum packed in
plastic bags and were frozen in a freezer at -20°C until needed for
experim ents.
All frozen roasts were thaw ed in a refrigerator at 4°C
for 3 days until an internal tem perature o f 4°C was reached before
cooking.
All visible fat and alm ost all epim ysium was removed.
67
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A fter thawing, the m uscles were trim m ed to approxim ately the sam e
size and rectangular shape and w eight of 1.5 kg.
Cooking m ethod
Each roast was placed in a glass roasting pan (33 x 23 x 5 cm)
and cooked uncovered, using three different pow er levels in the
m icrow ave oven (40%: about 256 w atts, 60%: about 360 watts and
100%: about 575 w atts) until it reached an internal tem perature of
60, 70 and 80°C, including post processing tem perature rise (PPTR).
Each roast was turned over in the m iddle of the estim ated cooking
time.
The roast w as rem oved from the oven at a low er tem perature,
w hich was determ ined during prelim inary tests, to reach the desired
final internal tem perature.
Internal tem perature was m easured by a
Dickson T em probe 500 when the roast was rem oved from the oven.
Sam ple
p re p a ra tio n
Sam ples fo r chem ical and physical determ ination w ere
prepared as described in C hapter 3.
M easurem ent o f characteristics o f roasts
All o f the follow ing m easurem ents were made w ith the
procedures d escrib ed in C hapter 3.
M easurem ents w ere cooking
time, standing tim e, PPTR, cooking losses, m oisture, fat, protein and
thiam in co n ten t and retention, w ater holding capacity, shear and
com pression v alu es and solubilized collagen content.
R e s u lts
and
d is c u s s io n
Two-way ANOVAs did not indicate any significant differences
(P> 0.05) due to interaction o f pow er level and internal tem perature.
68
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Significant differences (P<0.05) shown in the tables are based on one­
way ANOVAs, which w ere calculated when tw o-w ay ANOVAs
showed significant treatm ent effects but no interaction.
Fishers PLSD
was used for m ean separation.
Cooking time, standing tim e and PPTR
Table 14 shows final internal tem perature, cooking time,
standing time and PPTR o f roasts.
Final internal tem peratures of
roasts were the highest internal tem peratures m easured after
rem oving roasts from the m icrowave oven and allow ing them to
reach maximum tem perature.
tem peratures.
M ost roasts reached the desired
How ever, the roasts of internal tem perature of 80°C,
cooked with 40% m icrow ave power, had lower final internal
tem peratures
than
expected.
Cooking time was calculated as min per kg w ithout including
standing time.
There w ere significant differences in cooking times
among different m icrow ave pow er levels and different internal
tem peratures.
The low er the internal tem perature of roast, the
shorter the cooking tim e.
The lower the microwave pow er level of
cooking, the longer the cooking time.
Standing time is the tim e between rem oval o f the food from
the oven until it finishes cooking.
In prelim inary tests, the standing
tim e to reach the desired tem peratures (60, 70 and 80°C) was
estim ated at 14 to 23 min with a average of 18 min.
Pow er level did
not significantly affect the standing time, nor did the internal
tem perature.
The standing tim e of roasts that w ere cooked to an
69
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Table 14. Final internal tem perature, cooking time, standing tim e
and PPTR o f roasts cooked to three different internal
tem peratures w ith three different m icrow ave pow er levels.
Internal temoerature
60°C
Characteristics
70°C
80°C
5 9 !l± 1 .8 9 a
69.16±0.28b
76.67±0.67Ac
*
60%
58.74±2.16a
68.04±0.28b
81.50±1.61Bc
*
temp (°C) 100%
58.22±0.97a
70.56± 1.41b
80.20+0. lOBc
*
ns
*
Final
internal
Cooking
time
40%
SF
ns
40%
30,66±1.61aA
60%
(min/kg) 100%
Standing
time
(min)
*
15.79±1.21aC
23.94±0.77bC
*
40%
17.37±1.25
60%
*
17.25±1.23
ns
23.00±1.16a
17.50±2.50ab
14.25±2.38b
*
23.17i2.17
lo.00±2.52
19.72±2.96
ns
ns
40%
12.45±1.45
(°C)
60%
14.22±1.31a
SF
*
24.62±0.95bC
17.00±5.00
PPTR
100%
*
29.99+1.13abB 36.88±2.24bB
*
SF
45.02±0.33bA
24.77±1.47aB
SF
100%
44.16±2.64bA
SF .
ns
9.02±1.06A
12.60±0.28ABab
15.87±1.31B
14.52±0.67
*
ns
ns
7.36±1.79A
10.09±0.58Ab
18.34±2.78B
*
SF : Significance of F value: significant at 0.05 (*) level, ns: not
sig n ifican t.
Small letters show s significant differences by different internal
te m p e r a tu re s .
Capital letters shows significant differences by different m icrow ave
pow er levels.
70
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ns
*
ns
internal tem perature of 60°C with 60% and 100% m icrow ave power
level was a little longer than that of other treatm ents.
The short
tim e needed for cooking to low internal tem peratures m ight result in
longer standing tim es being needed to distribute heat to all areas of
the roasts.
The published reports showed a wide range o f standing
times for roasts.
Kylen et al. (1964) showed 20 min of standing time
for roasts w eighing 1.5 kg to reach an internal tem perature of 74.4°C.
K orschgen et al. (1976) showed 40± 11 min of standing tim e o f roasts
o f 1 kg cooked with 1054 watts of microwave power and 28±4 min
o f standing time of roasts of 1 kg cooked with 492 w atts of
m icrow ave pow er to an internal tem perature of 70°C.
There were some significant differences in PPTR among
different m icrow ave pow er levels at internal tem peratures of 70°C
and 80°C.
A greater increm ent o f PPTR was seen as m icrow ave
pow er level was increased.
Sawyer (1985) analyzed the duration
and extent of PPTR o f some products and observed that the quantity
and location of PPTR was not consistent within and am ong batches of
the same product and PPTR was product dependent.
The literature
shows a wide range of PPTR (Kylen et al, 1964; Korschgen and
Baldwin, 1978; Starrak, 1982).
The results of this study, as well as
earlier reports, suggest that the PPTR in Toasts can be substantial (up
to 20°C in a 20 min time period).
therefore, could be affected.
The quality of the final product,
The variation in cooking tim e per kg
depending on the size o f the roast, expected internal tem perature
and pow er levels used is also large.
Thus, it is essential to m onitor
m eat tem perature w ith a therm om eter or probe to produce
71
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consistently cooked roasts.
Cooking times per kg can only be used as
guidelines to approxim ate the am ount of tim e needed.
Cooking losses
Table 15 shows total losses, drip losses and evaporation losses
of roasts.
There were significant differences in total losses of roasts
cooked to three d ifferent internal tem peratures at all m icrow ave
pow er levels.
increased.
Total losses w ere increased as internal tem perature
M ost reports com pared conventional and m icrow ave
heating methods when m eat was cooked to tem perature of over 70°C,
and showed no differences in these param eters betw een the two
heating methods (K orschgen and Baldwin, 1978; Voris and Van
D uyne, 1979; Payton and Baldwin, 1985).
However, when Starrak
(1982) com pared the cooking loss of roasts cooked to an internal
tem perature of 62-65°C by m icrow ave and conventional m ethods,
there was a significant difference.
There are no reports about the
com parison of characteristics of microwave cooked roasts o f different
internal tem peratures.
Sanderson and Vail (1963) rep o rted that
total cooking losses w ere increased when three different beef
m uscles were cooked to constant internal tem perature o f 60, 70 and
80°C.
Lawrie (1985) cited their paper in his book and showed that
only p art of the increm ent o f cooking losses was due to loss of
m oisture.
This trend is also shown in this study.
72
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Table 15.
Total losses, drip losses, evaporation losses of roasts
cooked to three different internal tem peratures with
three differen t m icrow ave pow er levels.
Internal temperature
60°C
Characteristics
70°C
SF
80°C
Total
40%
22.62±2.38a
33.21±2.08b
37.56±1.18b
*
losses (%)
60%
26.08±2.40a
33.39±3.19ab
38.96±0.03b
*
100%
28.98± 1.60a
34.06±1.61ab
39.90±0.62b
*
ns
ns
SF
Drip
40%
6.89±0.93
losses (%)
60%
7.41±0.66
8.59±0.24AB
100%
8.59±0.19a
5.77±0.54bB
SF
Evaporation 40%
losses (%)
60%
100%
SF
Evaporation 40%
ratio
60%
100%
SF
10.21±2.09A
*
ns
15.73±1.54a
18.67± 1.75a
20.39± 1.79a
0.70±0.02
10.54±1.05
ns
7.19±1.57
ns
7.24±1.27ab
*
ns
22.99±1.00bA
27.01±0.79cA
*
24.82±3.28ab
31.77±1.55bB
*
28.29±1.93bB
32.66±1.89bB
*
*
ns
ns
0.68±0.10A
*
0.72±0.02
ns
0.72±0.004a
0.71±0.02ABab
0.82±0.04b
*
0.70±0.02a
0.83±0.02Bb
0.82±0.04b
*
*
ns
ns
SF : Significance of F value: significant at 0.05 (*) level, ns: not
sig n ifica n t.
Sm all letters show s significant differences by different internal
te m p e r a tu re s .
C apital letters shows significant differences by different m icrow ave
pow er levels.
73
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Table 16 shows a com parison of the Sanderson and Vail (1963)
study and current study with respect to m oisture content, cooking
loss and moisture loss o f bovine SM muscle cooked to three different
internal tem peratures.
M oisture loss in this table is calculated as the
difference betw een m oisture content of raw m eat and that of meat
cooked with 100% m icrowave power.
If these two studies are used
to com pare the difference between conventional and m icrow ave
heating, it appears that there are differences in cooking loss,
m oisture loss and m oisture content between the two different
heating m ethods at internal tem perature of 60°C; how ever, there are
no differences in these param eters between two different heatings at
internal tem peratures of 70 and 80°C.
Table 16.
Therefore, the internal
Effect of different internal tem perature on cooking loss,
m oisture loss, moisture content of roast cooked with
m icrow aves and conventional heating m ethods.
Internal te m p e ra tu re f^ O
60
70
80
Cooking loss (% WB)
10.9
33.7
4 2 .8
5.6
9.6
14.0
M oisture content
6 8 .8
62.2
6 0 .0 c o n v e n tio n a l
Cooking loss (% WB)
2 9 .0
34.1
3 9 .9
Moisture loss (% WB)
10.6
11.7
16.3
Current study
M oisture content
6 3 .4
62.3
57.7
microwave**
Moisture loss*(% WB)
Sanderson & Vail
*: M oisture content of raw muscle- m oisture content of cooked roasts
**: Full power
74
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tem perature may be a factor to consider when com paring heating
m e th o d s.
The three different m icrow ave pow er levels had no effect on
total losses at each internal tem perature (Table 15).
A lthough the
total losses of roasts cooked to an internal tem perature of 60°C with
three different pow er levels were not significantly different, they
tended to increase as m icrow ave pow er level increased.
This trend
was also seen in Starrak's report (1982), w hich com pared three
different m icrow ave pow er levels in roasting beef top round roasts
cooked to an internal tem perature of 62-65°C.
However, when two
d ifferent m icrow ave pow er levels w ere com pared w ith roasts cooked
to an internal tem perature o f over 70°C (Korschgen et al., 1976; Drew
et al., 1980), no difference in total losses were observed.
phenom enon was also found in the present study.
This
This result m ight
suggest that there is a great change in m uscle com ponents betw een
60 and 70°C and m uscle com ponents could be affected by heating
rates and cooking m ethods.
It is know n that m eat cooked quickly to a given internal
tem perature had a low er cooking loss and was m ore juicy than that
cooked slow ly to the same tem perature because coagulation of the
proteins on the surface o f m eats during roasting inhibited loss of
fluid (A ndross, 1949; Bram blett and Vail, 1964).
This was not
observed in the m icrow ave cooked m eat, probably due to the lack of
surface brow ning and d ifferent heating patterns in the m icrow ave
oven as com pared to the conventional oven.
75
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D rip losses of roasts showed inconsistent differences among
d ifferent m icrow ave pow er levels and different internal
tem peratures (Table 15).
However, there was a significant difference
in evaporation losses am ong different m icrow ave pow er levels and
d ifferent internal tem peratures.
Evaporation losses w ere increased
as internal tem perature of roasts was increased and m icrow ave
pow er level was increased.
Because total losses depend on the drip
losses and evaporation losses, there is a shift in the kinds of losses
that occur at higher internal tem peratures and pow er level.
Longer
cooking tim e and higher m icrow ave pow er resulted in greater
evaporation from both m eat and drippings.
The ratio o f evaporation
losses to total losses of roasts m ight be another way to com pare the
drip losses and evaporation losses of roasts.
From Table 15, it can be
seen that there was no difference in the ratio of evaporation losses to
total losses of roasts cooked to an internal tem perature o f 60°C
among three different m icrow ave pow er levels.
H ow ever, the
evaporation ratio was increased as m icrowave pow er level was
increased for the roasts cooked to internal tem peratures of 70°C and
80°C.
A t 40% m icrow ave power levels, there was no significant
difference in the evaporation ratio of roasts cooked to three different
internal tem peratures.
B u t at the other tw o m icrow ave pow er levels,
there w as a significant difference in the evaporation ratio of roasts
cooked to three differen t internal tem peratures.
M oisture, fat and protein content
T able 17 shows the m oisture, fat and protein contents o f roasts
cooked to three d ifferen t internal tem peratures w ith three different
76
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m icrow ave pow er levels.
For the m oisture content, there was no
significant difference among three different pow er levels at all
internal tem peratures.
How ever, m oisture content in roasts cooked
to internal tem peratures o f 60 and 70°C was significantly higher than
in roasts cooked to an internal tem perature of 80°C.
As shown in
Table 18, Kylen et al. (1964) found significant differences between
m oisture content of m icrow ave cooked beef rib roast heated to an
internal tem perature of 76°C and conventionally cooked roasts
heated to an internal tem perature of 64°C; those m oisture contents
were 49% and 58% respectively.
W hen Baldwin et al. (1976)
com pared m oisture content of beef cooked by three different cooking
m ethods, high and low m icrow ave pow er and conventional cooking
m ethods, there were significant differences am ong m ethods.
The
percent m oisture of high pow er m icrow ave (1054 watts) cooked
roasts and low er pow er m icrow ave (492 watts) cooked roasts was
52.9 and 53.5% respectively and conventionally cooked roasts of
internal tem perature of 70°C was 59.5%.
Korschgen and Baldwin
(1978) reported the m oisture content of roasts cooked w ith
m icrow ave and conventional m oist heat m ethods to an internal
tem perature of 98°C, which w ere 55.8% and 57.2% respectively and
show ed no significant difference.
Voris and Van Duyne (1979) also
show ed that the m oisture contents of the cooked roasts to an internal
tem perature of 68.3°C w ith m icrow ave and conventional m ethods
77
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Table 17.
Moisture, fat and protein content of roasts cooked to
three different internal temperatures with three
different microwave power levels.
Internal temneratures
Characteristics
Moisture
40%
content
60%
(%)
100%
SF
Fatc
content
(%)
40%
60%
100%
SF
Fatd
content
(%)
(%)
Protein^
content
(%)
6 2 .3 4 ± 1 .9 9
ns
4.24±0.57
5.88±0.83
ns
5.43+0.55
3 .4 9 ± 0 .9 2
4.37±0.70
5.88±0.75
ns
ns
80°C
58.42+0.68b
57.99±0.60b
5 7 .7 1 ± 1 .86
SF
*
*
ns
ns
6 .9 4 ± 1 .0 7
ns
ns
ns
6.0 3 ± 0 .4 3
5.60±1.15
12.01±1.10
15.70±2.15
1 1.91±1.72
14.57±1.38
9.38±2.45
15.47±1.48
13.05±4.15
60%
ns
28.4 1 ± 1 .3 6 a
29 .6 9 ± 1 .3 4
ns
ns
3 2 .3 0 ± 1 .0 5 a b 34.49± 1.42b
3 3.86± 3.46A B 35.43±0.83
100%
3 1 .6 9 ± 0 .2 1 a
3 3 .2 7 ± 1 .2 5 a b 3 5 .8 3 ± 0 .7 5 b
SF
40%
ns
8 1 .01± 1.74
ns
86.92± 2.87
ns
83.02± 4.14
ns
7 9 .3 3 ± 2 .2 6 A
86.9 4 ± 2 .1 9 B
89.28± 6.89
8 8 .6 9 ± 4 .8 3
8 4 .3 5 ± 1 .9 1
8 4 .8 1±1.96
ns
ns
ns
ns
40%
60%
100%
40%
60%
100%
SF
M oisture:
protein
ratio
6 4 .9 4 + 1 .4 0 a
6 2 .6 0 ± 0 .9 3 a
6 3 .5 2 ± 0 .6 9
70°C
6 2 .8 3 + 0 .4 7 a
62.84± 0.78a
ns
16.61±3.91
1 4 .3 1 ± 1 .57
SF
Protein0
content
60°C
40%
60%
100%
2 .3 0 ± 0 .1 6 a
2 ,1 2 ± 0 .1 2 a
2.01±0.01a
1 .9 5 ± 0 .0 6 ab
1 .9 0 ± 1 .2 0 ab
1 .8 8 ± 0 .1 1 ab
'
ns
ns
ns
*
ns
*
ns
1.70±0.07b
1 .6 4 ± 0 .0 5 b
1 .6 1 ± 0 .0 9 b
*
ns
ns
SF
ns
ns
ns
SF : Significance o f F value: significant at 0.05 (*) level, ns: not
sig n ific a n t
Sm all letters show s significant differences by different internal
tem peratures.
C apital letters shows significant differences by
different m icrow ave pow er levels.
c: wet basis, d: m oisture free basis, d: moisture and fat free basis.
78
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Reproduced
with permission
Table 18.
Comparison of moisture content of earlier studies of microwave heating of meat.
of the copyright owner.
B eef muscle
Wt
B oneless rolled rib
1.5 k g
L ongissim us dorsi
Further reproduction
T op round
Top round
prohibited without permission.
Top round
1 .2 k g
1.5kg
1.9 k g
0 .5 k g
C ooking m ethod IT
Moisture
SD
R e fe re n c e
MW
76°C
49%
a
Kylen et al. (1964)
OON
64°C
58.2%
b
MW-H
70°C
52.9%
b
MW-L
70°C
53.5%
b
OON
70°C
59.9%
a
M W (weit)
98 °C
56%
Korschgen and Baldwin
CON(wet)
98°C
57%
(1 9 7 8 )
MW
68°C
60%
Voris and Van Duyne (1979)
OON
68°C
60%
MW-CONV
70°C
59%
CONV
70°C
60%
OON
70°C
60%
Baldwin et al. (1976)
Payton and Baldw in (1985)
IT=internal tem perature, SD =significant difference, H=high, L=low , M W =m icrow ave, MWCO N V =m icrow ave-convection, CO N =conventional, CO NV=convection w et=m oist heat cooking
m ethod and other cooking m ethods are all dry heat cooking methods.
were not significantly different.
roasts were 60.4% and 59.7%.
The mean m oisture contents of the
Payton and Baldw in (1985) showed no
difference in m oisture content among three different cooking
m ethods, m icrow ave-convection, forced-air convection and
conventional methods.
The m oisture content o f roasts cooked to an
internal tem perature of 70°C w ith three cooking m ethods were 59%,
60% and 60% respectively.
According to Table 18, it seems that the
m oisture content is not affected by the cooking appliances (e.g.,
m icrowave vs. conventional), but it is likely to be influenced by the
cooking methods (e.g., roasting and braising).
From Table 16, it is interesting to observe the changes in
cooking loss, m oisiuic loss and m oisture content at different internal
tem peratures.
It is believed that the increm ent o f cooking loss
between 70 and 80°C is mainly due to m oisture loss.
However,
m aterials other than m oisture w ere probably solubilized at 60 and
70°C and contributed to increased cooking losses.
In this
tem perature range, m icrow ave heating m ight have solubilized m ore
m uscle com ponents than conventional heating.
There were no differences in fat content am ong three different
internal tem peratures and three different m icrow ave pow er levels.
This result is in consistent w ith other studies (K ylen et al., 1964;
Baldwin et al., 1976; K orschgen and Baldwin, 1978; V oris and Van
Duyne, 1979; Payton and Baldw in, 1985).
There was no difference in protein content on the wet basis
among the roasts cooked with three different pow er levels.
However, protein content o f roasts cooked to three different internal
80
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tem peratures were significantly different.
Baldwin et al. (1976)
found a significant difference in protein content of m icrow ave cooked
roasts and conventionally cooked roasts.
In contrast, K orschgen and
Baldw in (1978) did not find any difference in protein content of
roasts cooked with two different cooking methods.
inversely related to m oisture content.
Protein content is
The lower the m oisture
content of the roasts, the higher the protein content.
In the present
study, protein content was also calculated on m oisture-free basis and
the ratio of moisture to protein content.
When protein content was
com pared on the m oisture-free basis, there is no significant
difference in protein content among treatm ents.
H ow ever, there is
significant difference in m oisture to protein ratio among different
internal tem peratures.
The ratio of m oisture to protein tends to
decrease as internal tem perature is increased.
W ater holding capacity
Table 19 shows water holding capacity (WHC) o f roasts cooked
to three different internal tem peratures with three different
microw ave power levels.
There a was significant difference in WHC
of roasts cooked to an internal tem perature of 60°C among three
different m icrow ave pow er levels.
As microwave pow er level was
increased, the WHC was decreased.
This trend is also seen in total
losses o f roasts cooked to an internal tem perature of 60°C.
However,
at internal tem peratures o f 70 and 80°C, the WHC of roasts cooked
w ith three different pow er levels did not differ.
For the roasts
cooked to three different internal tem peratures, there w ere
significant differences in WHC o f roast cooked with different
81
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m icrowave pow er levels except at the 100% m icrow ave pow er level.
The trend is consisten t with the findings of Sanderson and Vail
(1963) and Laakkonen et al. (1970).
The higher cooking loss and
lower WHC of roasts cooked to an internal tem perature of 60°C with
full power than at low er microwave power levels is thought to be
due to rapid coagulation and disruption of protein and protein
network, resulting in the exudation of free w ater from the muscle.
This is not observed at higher internal tem peratures because the
surface d en atu ratio n prevents m oisture loss.
Table 19. W HC o f roasts cooked to three different internal
. tem p eratu res w ith three different m icrow ave pow er
le v e ls.
Internal tenroeratures
Characteristics
WHC
60°C
40%
Q .7 9 1 ± 0 .0 0 8 aA
60%
70°C
80°C
SF
0 .7 6 4 ± 0 .0 0 3 a b
0.739±0.016b *
0 .7 7 5 ± 0 .0 0 9 a A B
0 .7 5 2 ± 0 .0 0 9 ab
0.740±0.008b *
100%
0 .7 5 5 ± 0 .0 0 8 B
0.752±0.008
0 .7 3 6 ± 0 .0 2 3
SF
*
tn o
1
1o
ns
r\ c
11 O
SF : Significance of F value: significant at 0.05 (*) level, ns: not
sig n ific a n t
Small letters show significant differences by different internal
te m p e r a tu re s .
Capital letters show significant differences by different microwave
pow er levels.
82
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Thiamin content and thiamin retention
Table 20 shows thiam in content and retention of roasts cooked
to three differen t internal tem peratures w ith three different
m icrow ave pow er levels.
There were no significant differences in
thiam in content and retention of roasts cooked with three different
m icrow ave pow er levels to each internal tem perature.
H owever,
there were significant differences in thiam in content and retention
among roasts cooked to internal tem peratures of 60, 70 and 80°C at
Table 20
Thiam in content and retention in roasts cooked to three
d iffere n t in tern al tem peratures w ith three different
m icrow ave pow er levels.
Internal temoeratures
60°C
70°C
Characteristics
Thiam in^
(mg/100g)
40%
60%
100%
SF
Thiamin6
fmcr/l
00 cr)
\ -----O ' — ~ o /
40%
60%
100%
SF
0 .1 1 6 ± 0 .0 0 7
0 .1 0 9 + 0 .0 0 5
0 .1 1 7 ± 0 .0 0 8
ns
0 .1 2 9 + 0 .0 0 6
0 .1 3 1 + 0 .0 0 1
0 .1 2 2 ± 0 .0 0 3
ns
80°C
0 .1 0 2 ± 0 .0 0 3
0 .0 8 8 ± 0 .0 0 1
0 .0 9 3 + 0 .0 0 1
ns
SF
ns
ns
ns
0 .3 7 5 + 0 .0 2 6 a 0 .4 0 5 + 0 .0 2 0 a 0 .2 4 8 + 0 .0 1 5 b *
0 .3 3 0 ± 0 .0 3 9 a 0 .3 9 1 ± 0 .0 0 3 a 0 .2 4 2 ± 0 .0 0 4 b *
0 .3 6 2 ± 0 .0 2 3 a 0 .3 8 6 ± 0 .0 2 0 a 0 .2 5 2 + 0 .0 0 3 b *
ns
ns
ns
6 4 .4 8 + 2 .8 7 a 4 4 .1 9 + 2 .5 8 b *
6 0 .4 5 ± 4 .9 3 a 4 3 .2 1 + 0 .6 8 b *
6 6 .3 4 ± 1 .4 3 a 4 5 .0 9 ± 0 .4 5 b *
(%)
ns
ns
W et basis. e: M oisture and fat free basis
SF: Significance of F value: significant at 0.05 (*) level, ns: not
significant. Sm all letters show significant differences by different
in te rn a l te m p e ra tu re s.
Thiamin
Retention
40%
60%
100%
SF
6 6 .9 6 + 4 .6 0 a
6 5 .8 1 + 2 .0 6 a
6 4 .7 6 + 4 .10a
ns
83
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every m icrow ave pow er level.
Thomas et al. (1949) reported the
thiamin retention o f roasts weighing 1.35 kg to 1.80 kg, cooked to an
internal tem perature o f 74°C by using electronic range and electric
oven.
The thiam in retentions of roasts cooked w ith electronic range
and electric range were 63% and 75% respectively.
Dawson et al
(1959) investigated the thiam in retentions of thin cut (3.8 cm thick)
of top round beef m uscle, which was roasted at 177°C, and thick cut
(7.6 cm thick) o f top round beef muscle, which was roasted at 149°C.
Both roasts were cooked to an internal tem perature of 80°C.
The
thiamin retention of thin cut was 66% and that of thick cut was 72%.
They also com pared the thiam in retentions of m eat cooked by two
cooking m ethods, oven braised and pressure braised, w hich w ere
cooked to an internal tem perature of 100°C.
The thiam in retention of
oven braised muscle was 31% and that of pressure braised m uscle
was 28%.
Kylen et al. (1964) com pared the thiam in retention of
roasts cooked by using electronic range with those of roasts cooked
by using gas oven.
The thiam in retention of roasts cooked to an
internal tem perature of 76°C by electronic range was 58% and that of
roasts cooked to an internal tem perature of 64°C by gas oven was
80%.
Baldw in et al. (1976) com pared three different cooking
m ethods in thiam in retention of m eat, m icrow ave oven operated
w ith 1054 w atts, m icrow ave oven operated w ith 492 w atts and
conventional oven at 163°C.
Thiamin retention of 1.2 kg longissimus
m uscles cooked to an internal tem perature o f 70°C with the three
cooking methods were 61%, 49% and 69%, respectively.
The thiamin
retention o f m uscles cooked with low power m icrow ave oven was
84
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significantly lower.
K orschgen and Baldwin (1978) showed
significant difference in thiam in retention of roasts cooked by m oistheat m icrow ave and by conventional oven to an internal
tem perature of 98°C, which were 25% and 19% respectively.
Table 21 shows thiam in retention of roast cooked by two
heating m ethods, which was reported in earlier studies.
From this
table, it seems that thiam in retention of meat was lower as
tem perature was increased.
study.
T hese trends also showed in the present
Baldwin et al. (1976) showed significant differences in
thiam in retentions between higher pow er m icrow ave and low er
pow er microwave.
However, the present study does not show any
difference in thiam in retention of three different m icrow ave pow er
levels.
Several reports m ention that the vitamin losses between
m icrow ave and conventional m ethods are com parable (V oris and
Van Duyne, 1979; Gerster, 1989).
According to the studies of thiam in
retention (Table 21), it is more likely to depend on internal
tem perature of roast than cooking m ethods.
Shear and com pression
m easurem ent
Table 22 shows the results of shear cohesiveness, shear
firm ness, com pression hardness, com pression springiness and
com pression cohesiveness o f roasts cooked to three different internal
tem peratures with three different m icrow ave pow er levels.
E xcept
com pression cohesiveness, the results did not show any significant
difference in the param eters for m ost treatm ents.
Sanderson and
Vail (1963) showed no difference in shear force of LD cooked to
internal tem perature of 60, 70 or 80°C.
However, there was a
85
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Reproduced
with permission
Table 21.
Comparison of thiamin retention of earlier studies of microwave heating of meat.
of the copyright owner.
Beef muscle
Wt
C ooking m ethod
IT
Thiamin retention
SD
Boneless rib
1.6kg
MW
CON
74°C
74°C
63%
15%
Thomas et al. (1949)
Top round
th in
th ic k
CON
OON
CON(wet)
P re ssu re
80°C
80°C
66%
72%
Dawson et al. (1959)
100°C
100°C
31%
28%
R e fe re n c e
Further reproduction
prohibited without permission.
Boneless rolled
rib
1 .5 k g
MW
CON
76°C
64°C
58%
80%
a
b
Kylen et al. (1964)
Longissim us
dorsi
1.2kg
MW'-H
M W -L
CON
70°C
70°C
70°C
61%
49%
69%
a
b
a
Baldwin et al.(1976)
Top round
1.5kg
M W '(w et)
CON(wet)
98°C
98°C
25%
19%
K orschgen and Baldwin
(1 9 7 8 )
Top round
0 .5 k g
MW-CONV
CONV
70°C
70°C
Payton and Baldw in
(1 9 8 5 )
CON
70°C
70%
77%
76%
IT=internal tem perature, SD =significant difference, H =high, L=low , M W =m icrowave, MWCO N V =m icrow ave-convection, C!ON=conventional, C O N V =convection, w et=m oist heat cooking
m ethod and other cooking m ethods are all dry heat cooking m ethods.
Table 22.
Shear and compression measurement of roasts cooked to
three different internal temperatures with three
different microwave power levels.
Characteristics
60°C
Internal
70°C
temneratures
80°C
SF
Shear
40%
9 .2 5 ± 0 .1 4
9.9411.29
8 .2 0 1 1 .5 5
ns
cohesiveness
60%
8 .4 9 ± 1 .33
10.7 4 + 1 .4 2
9 .5 9 1 0 .1 5
ns
100% 11.50+1.24
SF
ns
8.11+0.78
ns
9 .5 6 1 1 .2 4
ns
ns
7 4 .2 0 ± 4 .9 0
8 4 .0 4 1 6 .3 9
7 0 .6 2 1 1 3 .9
ns
8 9 .0 1 1 6 .8 0
ns
(Kg)
Shear
40%
Firmness
60% 7 1 .7 7 ± 1 1.75 101.07±13.45
(Kg/min)
100% 8 2 .0 5 ± 4 .2 0
SF
ns
6 8 .8 9 1 9 .5 5
ns
9 9 .4 5 1 1 0 .7 8
ns
ns
Compression
40%
2 5 .2 5 1 3 .3 0
3 7 .6 7 1 3 ,9 7
3 6 .2 3 1 3 .7 3
ns
Hardness
60%
3 0 .5 5 1 0 .8 5
3 6 .2 3 1 3 .2 8
3 5 .6 3 1 2 .9 7
ns
100% 2 9 .8 3 1 1 .9 9
SF
ns
30 .7 9 + 3 .0 9
ns
3 4 .7 2 1 4 .7 8
ns
ns
(kg)
Compression 40% 0 .0 2 3 ± 0 .0 0 1 a A 0 .0 2 9 1 0 .0 0 2 ab 0 .0 3 2 1 0 .0 0 4 b *
Springiness
(min)
60% 0 .0 2 8 ± 0 .0 0 1 B
0 .0 3 3 1 0 .0 0 5
100% 0 .0 2 6 ± 0 .0 0 1 aA B G .0 3 6 ± 0 .0 0 1 b
SF
*
ns
0 .0 3 7 1 0 .0 0 2 n s
0 .0 4 1 i0 .0 0 1 c *
ns
Compression 40%
0 .3 3 1 0 .0 4
0 .3 4 1 0 .0 2
0 .3 1 1 0 .0 1
ns
Cohesiveness 60%
0.31+0.01
0.3310.03
0 .3 6 1 0 .0 1
ns
100%
0.3210.05
0.3710.07
0 .3 7 1 0 .0 6
ns
SF
ns
ns
ns
SF : Significance of F value: significant at .05 (*) level, ns: not
sig n ifica n t.
Sm all letters show significant differences by different internal
te m p e r a tu r e s .
C apital letters show significant differences by different m icrow ave
pow er levels.
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decreasing trend in the shear force for ST and SM as internal
tem perature of m eat was increased.
They believed that the different
reactions o f the m uscles to cooking was caused by varying connective
tissue content.
If the reports showing that m icrow ave heating
results in more collagen solublization (McCrae and Paul, 1974 ; Zayas
and Naewbanij, 1986) are correct, then the lack o f difference in shear
values of roasts of three different internal tem peratures in the
current study m ight be attributed to equivalent collagen
solublization in m icrow ave heated roasts at all internal tem peratures
to give com parable shear values even at low internal tem perature.
Collagen solubility is not significantly different at the three internal
tem peratures (Table 23), although there is a trend tow ard increasing
collagen solubilization as internal tem perature increases.
Davey and
G ilbert (1974) observed two separate phases of toughening during
increasing internal tem perature.
The first phase, occurring between
40-50°C, was due to the denaturation of the contractile proteins and
the second phase, occurring between 65-75°C, was due to fiber
shrinkage as collagen denatured.
The toughness o f m uscle
dim inished above 75°C as collagen breakdown occurred.
Therefore,
it show ed that collagen solubilization plays som e part in tenderness
o f meat.
Brady and Penfield (1981) investigated the textural
characteristics of beef sem itendinosus cooked conventionally to two
different internal tem perature (60 and 70°C) w ith tw o different
heating rates (slow and fast).
They showed no differences in
penetration hardness, cohesiveness, and chew iness and shear
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cohesiveness and firm ness of muscles in all treatments.
The reports
com paring tw o different heating rates by the m icrow ave pow er
levels did not show any significant difference in shear values
(Korschgen et al., 1976: Drew et al., 1980).
This current study shows
that there is no significant difference in Instron measured
tenderness of roasts cooked with three different m icrow ave pow er
levels to each internal tem perature.
There are no other reports
com paring shear values of meat cooked to different internal
tem peratures
by m icrow ave heating.
P ercent solubilized collagen
Table 23 shows percentage of collagen solubility of roasts
cooked to three different internal tem peratures w ith three different
m icrowave pow er levels.
The collagen content of raw SM muscle was
10.8 mg/g on wet basis, 44.88 mg/g as dry, fat free basis and 4.5% of
total protein.
It is well known that different m uscles and different
ages o f muscle differ in collagen content (Goll et al., 1964; Bendall,
1967; Cross et al., 1973; Dransfield, 1977).
Dransfield (1977) showed
that the total collagen content of meat from 18 month old steers
ranged from 2.2% in PM to 5.6% in complexus muscle; SM muscle had
4.09% collagen content on a dry, fat free basis.
The collagen content
of raw SM m uscle of this study, which is 4.49 % on dry, fat free basis,
is sim ilar.
W hen Bendall (1967) estim ated the collagen content of
different m uscles o f 18 to 24 months old steers, the collagen content
of SM m uscle was 2.9% collagen as % dry weight.
There are no differences in solubilized collagen contents of
roasts that w ere cooked with three different m icrow ave pow er levels
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at each internal tem perature.
M cCrae and Paul (1974) investigated
the effect of rate of heating on solubilization of collagen of beef
m uscles.
They show ed th at m icrow ave heat treatm ent solubilized
m ore collagen from the m uscles than did different conventional heat
treatm ents, w hich had low er heating rates.
Zayas and Naewbanij
(1986) com pared conventional heat and m icrow ave heat cooking
method in solubilization o f collagen of meat.
They found m icrowave
energy solubilized m ore collagen than did conventional heat energy.
However, it seem s that the different heating rates caused by
different m icrow ave pow er levels did not affect collagen
solubilization of roasts in the present study.
Table 23.
The heating
P ercent solubilized collagen of roasts cooked to three
d ifferen t in tern al tem peratures w ith three different
m icrow ave pow er levels.
Characteristics
Internal
temperatures
70°C
80°C
60°C
SF
40%
20.72±1.96
27.12±3.59
25.07±1.06
ns
£f\rtf
VV70
20.44±3.73
24.59±1.88
27.41±2.70
ns
100%
2G.45±2.36a
26.85±0.89b
25.94±0.16ab
*
SF
ns
ns
ns
SF : Significance of F value: significant at 0.05(*) level, ns: not
sig n ifican t.
Sm all letters show significant differences by different internal
te m p e r a tu re s .
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rate of lower m icrow ave power heating is still higher than that of
conventional heating.
The solubilized collagen contents increased with increasing
internal tem perature o f roasts at three different pow er levels.
The
percentages o f solubilized collagen of roasts of internal tem peratures
of 70°C and 80°C were similar.
However, the differences in
percentages o f solubilized collagen of roasts of three different
internal tem peratures w ere not significant, even though the percent
of solubilized collagen of roast of internal tem perature of 60°C at full
microwave power level was lower than those of roast of internal
tem perature o f 70°C at the same power level.
Zayas and Naewbanij
(1986) showed that percentages of solubilized collagen of four
different internal tem peratures (65, 80, 85 and 95°C) ranged from 27
to 31%.
Paul e t al. (1973) made four different internal temperature
comparisons in collagen solubility (58, 67, 75 and 82°C) and ranges of
percentages o f solubilized collagen of four different internal
tem perature were 4.25 to 11.03%.
Cross et al. (1973) showed heat
soluble collagen o f SM muscle was 4.31% when sample was held at
77°C for 70 min.
Dransfieid (1977) reported 13.7% of heat soluble
collagen o f SM m uscle when sample was held at 90°C for three hours.
Jerem iah and M artin (1981) showed 13.89 to 17.97% heat soluble
collagen at 70°C for 70 min with LD muscle.
Burson and Hunt (1986)
reported that heat soluble collagen at 70°C for 70 min of LD muscle
was 10.2±1.4% and that at 90°C for 140 min was 34.7±1.4% .
The degree o f collagen solubility in several studies varies even
in the sam e tem perature treatment.
H eat soluble collagen can be
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calculated from the soluble fraction o f sample by dividing by the
am ount of heat soluble plus insoluble collagen.
However, the
calculation of solubilized collagen is not specified clearly in some
r e p o rts .
To com pare collagen solubility with other studies, guides in
collagen solubility calculation are needed.
W hen the collagen content
o f raw and cooked samples on w et basis w ere compared, collagen
content of cooked samples was higher than raw sample, because of
m oisture loss.
W hen the collagen contents of raw and cooked
samples on a m oisture- and fat- free basis or as collagen N over total
N, collagen content o f cooked samples m ight be higher or low er than
that of raw m uscles.
The com parison of collagen contents o f raw and
cooked m uscles is m eaningless with respect to solubilized collagen.
A lternatively, the sum of collagen contents o f drippings and cooked
m eat can be used as total collagen.
The total collagen of residues of
cooked m eat can be used as the insolubilized part of collagen.
In this
m ethod, analysis o f drippings is needed and sometimes, it is difficult
to get the exact am ount of drippings.
Therefore, in order to calculate
the solubilized collagen content of m uscles after cooking, it is
suggested that the percentage of solubilized collagen be calculated
from total am ount of collagen in total residues of cooked m uscle
divided by total am ount o f collagen in total raw muscle.
Table 24
shows correlations o f percent solubilized collagen and Instron
m easurem ents, b u t these were not significant (p>0.05).
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Table 24. C orrelation o f collagen solubility and Instron m easurem ent
of ro ast cooked to three different internal tem peratures.
SC
SF
60
0.139
0 .5 5 7
70
-0 .3 0 4
80
0.332
°c
CH
CS
CC
-0 .180
-0.368
0 .2 6 9
-0 . 1 9 0
0.195
0.131
0 .0 1 2
0.121
0.519
0.5 0 9
0.0 97
SC: Shear cohesiveness. SF: Shear firmness. CH: Compression
hardness. CS: Com pression springiness. CC: Compression
c o h e siv e n e ss.
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Chapter 5
U ltra s tru e tu ra l
C hanges
D u rin g
of
B o v in e
M ic ro w a v e
S e m im e m b ra n o s u s
M u scle
H e a tin g
Introduction
Tenderness is the m ost im portant factor in judging meat
quality.
Much research has been done to explain what influences
tenderness o f meat, as evaluated by physical m ethods, sensory tests
or m icroscopic exam ination.
In general, the results of physical
m easurem ents did not relate well to sensory tests.
M ost microscopic
exam ination of meat was done with light m icroscopy.
Transm ission
electron m icroscopy (TEM ) gives better resolution of the tissue
structures.
The objective of this study was to investigate the
ultrastruetural changes o f m yofibrillar tissue of sem im em branosus
(SM) beef muscle w eighing 1.5 kg, cooked to different internal
tem peratures (60, 70, 80°C) with three different m icrow ave pow er
levels (40, 60, 100%).
M a te r ia ls
S am ple
and
m e th o d s
prep aratio n
W hole SM beef m uscle roasts, obtained from USDA Choice
G rade carcasses, were purchased from M eat Science Laboratory at
U niversity of Illinois.
after purchasing.
at -20°C.
Raw m uscle samples were fixed imm ediately
All SM beef m uscle roasts were frozen in a freezer
Thawed raw muscle samples were also fixed on the day of
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cooking.
For the microwave cooked meat, 1.5 kg roasts were cooked
using three different m icrowave pow er levels (40, 60 or 100%) until
m eat reached three different internal tem peratures (60, 70, or 80°C,
including PPTR) as described in Chapter 4.
From the three
replications o f each cooking treatm ent, roasts chosen for
ultrastructure study were which those w ere closest to the desired
internal tem peratures.
A fter the roasts were cooled at room
tem perature, muscle samples ( 4 x 4 x 4
cm) were taken 2.5 cm from
the center of the roasts and cut into blocks for light microscopy and
transm ission electron m icroscopy.
L ight m icroscopy
A pproximately two 1 x 1 x 1 cm m uscle blocks were removed
from muscle samples.
Muscle blocks were fixed in buffered 10%
formalin solution for 30 min and
m uscle slices.
2 weeks.
further sliced into 1 x 1 x 0.2 cm
Muscle slices were fixed in buffered 10% form alin for
The fixed tissues were processed through a Tissue-Teck
vacuum infiltration processor and em bedded in paraffin wax.
Transverse and longitudinal 5 |im sections were cut with a rotary
m icrotom e and mounted on glass slides.
The sections were stained
with V erhoeff elastin stain and counterstained with Picro-Ponceau
(H um ason, 1979).
Photographs were taken using Olympus light
m icroscope BH-2 with an installed cam era.
T ransm ission
electron m icroscopy
A m uscle block (1 x 1 x 0.3 cm) was taken from muscle
samples for TEM.
For the perim ysial collagen, samples were taken
near the m uscle samples for electron and light m icroscopy.
M uscle
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fiber bundles were rem oved and small pieces o f perim ysium w ere
taken for electron m icroscope work.
These sample blocks were fixed
for 30 min in m odified K arnovsky’s fixative.
M odified K am ovsky's
fixative was made with a m ixture of 2% paraform aldehyde and 2%
glutaraldehyde in 0.1 m phosphate buffer.
Samples were cut
lengthwise into small pieces from fixed blocks.
further fixed at 4°C for 24 h in the fixative.
M uscle sam ples w ere
Then each sample was
w ashed three tim es with 0.2M sucrose in 0.1M phosphate buffer for
15 min at room tem perature.
The samples were allowed to wash
overnight in a fourth change.
They were then rinsed with 0.1M
phosphate buffer (twice, 1 m in each).
Samples were post fixed with
1.3% 0 s 0 4 and Ruthenium Red in 0.1M phosphate buffer at pH 7.2 at
room tem perature for 1 h and then rinsed with 0.1M phosphate
buffer (tw ice, 1 min each) and washed with distilled w ater three
tim es (Hayat, 1981).
The sample was dehydrated with acidified DMP
(dim ethoxypropane, 3 tim es, 5 min each), filled with 50/50
DM P/acetone for 5 min, and then filled with 100% acetone for 5 min
2 tim es.
It was infiltrated with a m ixture of acetone:em bedding
m edia (Table 25) at the ratio of 1:1 for 1 h and continued infiltration
with the m ixture of acetone:em bedding media at the ratio of 1:3
overnight a t room tem perature.
N ext day the sample was em bedded
in pure em bedding m ixture on the flat mold and polym erized w ith
the em bedding m ixture at 70°C for 72 h and the polym erized m olds
w ere cured at room tem perature for 1 day.
Thin sections o f 50-100
nm were cut w ith a LKB III ultram icrotom e, stained with 20% uranyl
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nitrate and then w ith lead citrate and exam ined with H itachi H-500
TEM operated at an accelerating voltage of 75KV.
Table 25. Form ula for em bedding media (1:1 m ixture of M edcast
and Spurr's)
M ed cast
M e d c a st
DDSA
NMA
D M P -30
9.8
3.4
8.3
0.4
S p u r r ’s
ml
VCD
5
ml
DER 736 3.5
ml
NSA
13
0.2
ml_______ DM AE
ml
ml
ml
ml
M edcast com ponents w ere m ixed except for DM P-30 with
Spurr's com ponents except for DM AE at the ratio of 1:1. And then
DM P-30 was added follow ed by DM AE and mixed thoroughly.
M easurem ent o f sarcom ere length
To exam ine sarcom ere changes during heating, at least two
m uscle blocks were sectioned.
From those sections, more than four
grids w ere exam ined and m ore than tw enty electron m icrographs
w ere taken for the sarcom ere, and m ore than ten electron
m icrographs were taken fo r perim ysial collagen at the m agnification
o f 4800 x.
sarcom eres.
treatm ent.
Each electron m icrograph contains at least 100
Therefore, 2,000 sarcom eres were com pared at each
Sarcom ere lengths o f the same form of sarcom ere were
com pared for different h eat treatm ents.
lengths w ere m easured.
M ore than 130 sarcom ere
Electron micrographs of som e fine
endom ysium s w ere also taken.
Figures and tables referred to in the
text can be found at the end o f Chapters 5 and 6.
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Results
and
discussion
Raw m uscle
Figure 9 shows the longitudinal appearance of raw SM muscle
fibers observed by light microscope.
are seen.
Some cracks in m uscle fibers
This kind of longitudinal appearance of m uscle fibers was
also found by Paul et al. (1952), who com pared the histological
changes of bovine ST m uscle post slaughter, after various periods of
cold storage, from 0 h to 149 h.
The appearance of muscle fibers in
the current study is sim ilar to that of m uscle stored for 149 h.
A lthough the exact time elapsed post slaughter is not known for the
m uscles in the current study, it would be at least 72 h.
The appearance of the sarcom eres that were found on TEM
m icrographs during this experim ent can be classified as different
forms.
These have been designated as Forms A to G, and are
referred to as Types A to G in the figures and tables.
Figure 10
shows a TEM m icrograph of raw bovine SM muscle.
Three different
sarcomere forms (Form A, B and C) can be seen in a small area of
muscle.
The Form A sarcomere shown in Figure 11 has the well-
known contracted sarcom ere appearance.
The M -line, H -zone, A
band, narrow I band and intact Z-line can be distinguished.
The
spaces between the m yofibrils o f current raw m uscle samples were
larger than those seen by Kasang and Strom er (1986).
These large
spaces between the m yofibrils may be due to the relatively long
storage time after death o f anim al.
Kasang and Strom er (1986)
com pared the appearance of sarcom eres o f bovine LD m uscle which
was fixed right after death and at 24 h postm ortem .
The muscle
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fibers fixed at 24 h post mortem had greater spaces between the
m yofibrils and shorter I band than those fixed at death.
Studies of
porcine m uscle showed Z-lxne damage in m yofibrils on the carcass for
24 h postm ortem , and Z-line damage was much more extensive in
the white fibers compared to red fibers (Dutson et al., 1974; Abbott
et al., 1977).
However, the current study shows that m ost Z-lines
stayed intact, even though there was a relatively long handling time
before fixation.
Figure 12 shows the connecting pattern of Form A sarcomeres.
Continuous Form A sarcom eres were connected to several
discontinuous Form A sarcom eres repeatedly.
appearance may be due to the plane of slicing.
The discontinuous
Figures 13 and 14
show Form B and C sarcomeres, in which banding features are
difficult to distinguish.
The H-zone and I band are not easily
detected and the A band itself has dark and light regions.
Leander
(1977) named this dark A band feature as "pseudo-A" band.
Form B
sarcom eres in Figure 13 have
Form C
wide pseudo-A bands and
sarcom eres in Figure 14 have narrow pseudo-A bands.
In Figure
14,
the sarcom eres appear to come from a discontinuous section, but the
internal structure is evident.
The lengths of four different
form s of sarcom eres
SM muscle are also different, which is shown in Table 26.
found in raw
The
sarcom ere appearance of aged unheated LD m uscle from electron
m icrographs of Leander (1977) is sim ilar to Form C sarcom ere, and
that o f ST m uscle is similar to relaxed Form A.
The mean sarcom ere
length in LD muscle was 1.7 pm , and that in ST muscle was 2.4 p m .
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Leander stated that the difference was caused by more contraction of
sarcomere in LD than in ST muscle during 10 days of aging at 3°C.
However, the sarcomeres o f bovine LD muscle fixed at death, which
w ere exam ined by Kasang and Strom er (1986), were
relaxed Form A, and those fixed at 24 h
sim ilar to
post m ortem w ere similar to
Form F (Table 26).
To find an appropriate explanation for the sarcom ere
differences between the current
studies and previous
findings w ere com pared in four
ways.
1.
reports, the
Locker (1959) found four different types o f striation patterns
of sarcom eres of various ox muscles in rigor m ortis.
He said that
these represented various degrees of contraction from relaxation to
extrem e contraction of sarcom ere lengths of 3.7 to 0.7 pm .
These are
the fam iliar relaxed pattern nam ed Type I (3.7-2.4 pm ), a well
defined derivative pattern called Type II (2.4-1.9 pm ), a low contrast
interm ediate form nam ed Type III (1.8-1.5 pm ) and the well known
contraction pattern called Type IV (1.5-0.7 pm ).
Locker used
blended m uscle for electron m icroscope studies.
Later, he reported
that the approxim ate proportions of four fibril types of SM muscle
excised in rigor mortis were 2:3:3:2 from Type I to Type IV (Locker,
1960).
These four types o f striation patterns of sarcom ere are not
w ell m atched with the form s found in the present study.
2.
C heng and Parrish (1976) observed the ultrastructuTe of psoas
m ajor (PM) and LD with SEM.
They showed that PM muscle had
looser packing of m yofibrils, thinner m yofibril threads and w ider I
band regions than LD muscle.
Leander (1977) also showed a
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difference in sarcom ere appearance and length between the two
different m uscles.
Sarcom ere length o f different m uscles can be
changed depending on how the carcass was suspended during aging
(Locker, 1960; Herring et al., 1965; H ostetler et al., 1972).
Although
different tension during holding carcass vertically gave a difference
in sarcom ere length o f different muscles (Herring et al., 1965;
H ostetler et al., 1972), it is questioned w hether that tension also
creates the d ifference in sarcom ere appearance of different m uscles.
Because these different sarcom ere appearances were found in a
minute area such as 15 jim ^ in the current study, tensions during
holding carcass vertically m ight not be the only factor affecting
sarcom ere length and appearance.
The actual in vivo range in
sarcomere length of m uscle is not known.
The difference in
sarcom ere appearance in the present study is not well explained by
tension during aging.
3.
It is known that there are three types of m uscle fibers that can
be distinguished by histochem ical methods.
The three types of
muscle fibers (red, w hite and interm ediate or ocW, a R and PR) are red
fibers that contain m any m itochondrial oxidative enzym es; w hite
fibers that contain m any glycolytic enzym es; and interm ediate fibers,
w hich are betw een red and w hite fibers.
Cross sections of muscle
fiber that are stained for m itochondrial enzym e activity show a
m ixture of the three types of muscle fibers.
Fiber types have been characterized in a num ber o f ways.
Zapp and W ilson (1938) had shown that the concentrations of
carnosine and anserine, w hich are dipeptides, w ere greater in bovine
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w hite muscles than in bovine red muscle.
Lawrie et al. (1964) have
shown that bovine LD, a white muscle, had higher amounts of total
nitrogen and non-protein nitrogen than bovine supraspinatus and
retus femoris muscles, both o f which are red m uscles.
Cassens and
C ooper (1971) review ed the properties o f different fiber types and
found the biochem ical and histochem ical characteristics of porcine
m uscle to be sim ilar to those of other mammalian muscles.
They
m entioned that red m yofibrils have longer sarcom eres than white
m y o fib rils.
G authier (1970) showed that a relationship among different
m uscle types exists, using longitudinal sections of rat skeletal muscle.
F iber types could be distinguished according to num ber of
m itochondria and relative width and density of the Z-line.
sarcom ere appearance of all three types w as Form A.
had large m itochondria with closely packed cristae.
m itochondria were located at the I bands.
However,
The red fiber
Paired
Z-lines w ere w ider in the
red than in either the interm ediate or w hite fiber.
Interm ediate
fiber was sim ilar to the red fiber except th at m itochondria tend to be
som ew hat sm aller and their cristae less closely packed than in the
red fiber.
fiber.
Z lines were narrower in the interm ediate than in the red
W hite fibers had subsarcolem m al m itochondria that w ere
sparse, even in the nuclear region.
M itochondria consisted almost
entirely of the paired filam entous form at the I bands.
Z lines were
narrow est in this fiber.
Dutson et al. (1974) showed longitudinal appearance o f these
three types from porcine m uscle fibers.
They identified different
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fiber types of porcine muscle on the basis of the uitrastructure,
including num ber of m itochondria and density of the Z line, without
histochem ical staining.
Hunt and H edrick (1977) investigated the characteristics of five
im portant bovine m uscles within the same animal.
Significant
differences were observed among muscles for fiber types, crosssectional fiber area, sarcom ere length, visual color, percent
reflectance, m yoglobin content, hemoglobin content, w ater holding
capacity, transm ission value, pH, m oisture content, ether extractable
constituent and protein content.
For example, bovine red muscles
had higher ultim ate pHs than bovine white muscles.
Inner and outer
areas of the ST and SM muscles differed histochem ically in fiber
form and color.
The percentage of cc'W fiber in SM m uscle was
highest among three different fiber types.
They show ed that the
sarcomere length of the reddest muscle, such as PM , w as the longest
among five different m uscles and the sarcomeres of red portion of
the SM muscles were slightly longer that those of the w hite portion.
They used choice steer carcasses at 24 h postm ortem , and muscle
samples were frozen im m ediately after excision in isopentane that
had been cooled in liquid nitrogen, and stored on dry ice until
further processing and sectioning to 10 p.m.
The sarcom ere length of
SM was 1.83 |im .
Rao and G ault (1989) investigated the fiber com position and its
biochem ical characteristics.
In general, the predom inantly red fiber
form muscles had significantly higher pH values and total pigm ent
concentrations than the predom inantly w hite fiber form m uscles.
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These had significantly higher total nitrogen, non-protein nitrogen
and carnosine contents and also significantly higher acid buffering
c ap a cities.
There are no reports relating the three different fiber form s to
the longitudinal sarcom ere appearance of bovine m uscle sarcom eres.
The sarcom ere appearance that was observed in the present study
does not fit with longitudinal appearance of three types of rat
skeletal m uscle fiber found in the study o f G authier (1970).
There
are no studies show ing the longitudinal appearance o f different types
of m uscle fibers fo r bovine muscle.
4.
Johnson and B ow ers (1976) found both actively and passively
contracted fibers in neighboring m uscle fibers in a sm all area of
turkey breast m uscle, prim arily in 0 h m uscle.
A ctively contracted
m uscle fiber was sim ilar to Form A sarcom ere and passively
contracted m uscle w as sim ilar to Form G in current study, as shown
in Tables 27 and 28.
They suggested that passive contraction m ight
have been initiated by the cold fixative or by actively contracting
fibers.
Earlier, B endall (1960) identified passively contracted fibers
as those undergoing "supercontraction" and fibers contracting
"normally" as actively contracting fibers.
V oyle (1969) classified
kinked fibers as passively contracting and sm ooth fibers as actively
contracting.
Sarcom ere form s found in current study can not be
explained solely on the basis of contraction state.
Figure 15 show s the sarcom eres of frozen, thawed raw SM
muscle, which was nam ed Form D in current study (Table 26).
structural com ponents are well preserved.
All
The Z-line is intact.
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N arrow pseudo-A band, narrow I band and H -zone are seen; this
form differs from Form A in the appearance of the A band.
The
sarcom ere length in thaw ed m uscle (1.81 pm ) is longer than in fresh
raw m uscle (1.45 pm ).
This is in agreem ent w ith Johnson and
Bow ers (1976) w ho reported that sarcom ere length tended to
decrease and then increase as rigor developed and was resolved.
H ow ever, H egarty et al. (1973) found that sarcom ere lengths of
bovine PM m uscle w ere affected by aging, w hen m easurem ents were
made on unfixed sam ples using light m icroscopy.
W hen they
m easured corresp o n d in g fixed sam ples from electron m icrographs,
the differences w ere not significant.
They indicated that sampling
and fixation problem s m ight m ake m easurem ents m ade from
electron m icrographs difficult to interpret.
In frozen and thaw ed
m uscle, lots o f structural dam age was expected due to handling of
sam ples.
It w as surprising that thin and thick filam ents of m uscle
were w ell preserv ed and ice crystal dam age o f structure during
freezing and thaw ing was not seen in this study.
M icrow ave cooked m uscle
L ight m icroscopy
Figures 16, 17 and 18 show light m icrographs of longitudinal
appearance o f m uscle fibers cooked to an internal tem perature of
60°C w ith 40, 60 and 100% m icrow ave pow er levels, respectively.
Figure 19 show s lig h t m icrograph of longitudinal appearance of
m uscle fibers cooked to an internal tem perature o f 70°C w ith 40%
m icrow ave pow er level.
Figure 20 shows light m icrograph of
longitudinal appearance o f m uscle fibers cooked to an internal
105
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tem perature o f 80°C with 100% m icrow ave pow er level.
Figure 21
shows light m icrograph of longitudinal appearance of m uscle fibers
cooked to an in ternal tem perature of 80°C w ith 100% m icrowave
pow er level, w hich was sampled from the hardened outer surface of
ro a s t.
The histo lo g ical appearance of longitudinal m uscle fiber cooked
to an internal tem perature of 60°C and 70°C is different from the raw
muscle fiber (Figure 9), at all m icrow ave pow er levels.
W rinkling of
muscle fiber cooked to 60°C and 70°C is seen (Figures 16 to 19).
However, there is no appearance o f w rinkling of m uscle fiber when
m eat was cooked to 80°C (Figure 20).
The w rinkled appearance of
m uscle in the present study is sim ilar to that o f raw ST muscle stored
for 24 h o f cold storage from the study of Paul et al. (1952).
They
explained this as severe contraction in rigor state causing the
form ation o f rig o r nodes and Z-Z contractions, and this Z-Z contraction
was attributed to a passive w rinkling of uncontracted fibers.
However, because the muscle used in present study was aged, frozen
and thawed, this is not adequate to explain the w rinkled appearance
found.
Electron m icrographs (Figures 22 to 32) do not show any
evidence of rig o r nodes or heat rigor and Z-Z contraction of muscle
heated to 60°C .
Som e electron m icrographs (Figures 24 and 28) show
wavy appearance o f som e m uscle fibers.
T herefore, it can be
concluded th at the w rinkled appearance of m uscle fibers in light
m icrographs o f cooked m eat also show s wavy appearance in electron
m icrographs.
B u t this wavy appearance of m uscle fibers in electron
m icrographs also was found in raw m uscle.
B ecause the appearance
106
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o f Form A sarcom eres is the same in wavy muscle fiber or flat
muscle fiber, and there is no rigor node, heat rigor or Z-Z contraction,
it is possible that these differences in m uscle fiber structure can be
attributed to orientation of muscle fibers in vivo, not handling of
meat during processing.
Therefore, that difference m ight depend on
the portion o f m uscle that was photographed.
W hen m ultiple m uscle
sites are photographed, it is possible to find all form s of m uscle
fibers and appearance in any treatm ent.
The specific sarcom ere and
muscle fiber appearance may not be unique to a given heat
treatm ent or m ethod of cooking.
The structural changes of the outer surface of muscle cooked to
80°C is shown in Figure 21.
The texture was hard after the
concentrated m icrow ave heat treatm ent.
The appearance of m uscle
fiber is severely fragm ented and spaces betw een m uscle fibers were
reduced m ore than those of other treatm ents, due to dehydration.
Electron m icroscopy
Figures 22 to 53 show sarcom ere appearances in TEM
m icrographs o f bovine SM muscles cooked to 60°, 70° and 80°C with
three different m icrow ave power levels.
are visible in each treatment.
M any forms of sarcom eres
For exam ple, Figures 10, 22, 23, 27
and 37 show different sarcomere forms in a sm all area of raw and
cooked SM m uscle.
Based on the appearance of sarcom eres in the raw and cooked
meat, the different forms can be seen in Tables 26 to 28.
W hen Form
A sarcom eres are exam ined to com pare the effect of different
m icrow ave pow er levels and different internal tem peratures on
107
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muscle fibers, the appearance o f sarcom eres is quite sim ilar for all
treatments.
A ll characteristics o f the Form A sarcom eres such as Z-
band, H-zone, I band and A band are well preserved.
H ow ever, the
length of Form A sarcom eres was shortened as .the internal
tem perature and pow er level was increased.
In m eat cooked to 60°C, Form B Sarcomeres changed in length
and appearance (Table 26).
T he sarcom eres becam e m ore irregular
in size and shape (Figures 25, 29, 31).
A t higher internal
tem peratures, no Form B sarcom eres vrere found.
were not seen in any cooked m eat.
Form C sarcom eres
Only two other sarcom ere forms,
Form F (Figure 26) and E (Figure 32) were found in 60°C roast.
Sarcom eres in beef cooked to 70°C are classified in Table 27.
Form A sarcom eres (Figures 33, 38, 42) show typical structures.
The
other forms seen in 70°C roasts all present some loss of internal
structure due to denaturation o f proteins.
At 100% pow er levels,
sarcom eres appear shorter or fragm ented, and m ore coagulated
(Figures 43 to 45).
It should be noted that even those m icrographs
where the sarcom eres are discontinuous (Figure 42 or 45), the
ultrastructure can be seen clearly.
At 80°C, the sarcom ere structure looks dram atically different
(Table 28 and Figures 46 to 53).
The Form A sarcom eres retain their
structure, but are shorter than at other internal tem peratures.
All
other form s id en tified show substantial protein denaturation and loss
of m ost distinguishing bands and lines.
C om parisons o f electron m icrographs from this study with
others is com plicated by difference in muscles used as w ell as
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cooking method.
Schm idt and Parrish (1971) exam ined LD muscle
cooked to four different internal tem peratures.
Sarcom ere forms
sim ilar to those in the present study could be identified in electron
m icrographs.
In the raw muscle, Form C was found, Form A was
identified in 50°C and 70°C and the contracted Form F was seen in
70°C and 90°C.
In both studies, higher internal tem peratures
resulted in disintegration and coagulation of thin and thick filam ents.
At the highest tem perature, the structure becam e m ore am orphous.
Bouton et al. (1975) also showed no difference in sarcomere
length between raw and cooked m uscle to 60°C, and sarcom ere
length was shortened as tem perature and cooking tim e was
increased.
According to Cheng and Parrish (1976), m yofibril
fragm entation at Z disks after heating to 70°C is seen and the
structural changes of two m uscles (LD and PM) at different
tem peratures w ere different.
They explained that this may be due
to the loose packing of myofibrils unique to PM muscle.
Jones et al.
(1977) showed slight changes in sarcom eres at 50°C, but these were
readily apparent at 60 and 90°C.
Heating to higher tem peratures
caused fractures to occur increasingly at fiber surfaces and at Alines.
Sarcom ere banding feature o f muscle heated to 90°C was still
seen.
The findings of the present investigation generally confirm the
earlier work.
Therefore, it appears that ultrastructure of cooked beef
is affected by internal tem peratures regardless o f heat source.
Leander (1977) reported that the structure o f two m uscles (SM
and LD ) w ere different and structure was changed as tem perature
was increased by 5°C increm ents between 68°C and 73°C.
W hen
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their electron m icrographs w ere com pared with present study,
unheated ST muscle was sim ilar to Form A, unheated LD m uscle was
similar to Form C, ST m uscle heated to 63°C was similar to Form F, LD
muscle heated to 63°C was sim ilar to Form C, ST m uscle heated to
68°C is sim ilar to Form F, LD muscle heated to 68°C is similar to Form
B, ST muscle heated to 73°C is similar to Form A and LD muscle
heated to 73°C is sim ilar to Form H.
They also showed wavy
appearance o f Form B from LD muscle heated to 73°C which was
explained by rigor kink.
Leander attributed the changes in
sarcom ere form to the relatively m inor tem perature increase in the
cooked m eat.
How ever, the m ultiple forms observed in their electron
m icrographs could reflect the wide array present in any cooked
m u scle.
W hen the reports com paring conventional cooking with
m icrow ave cooking aTe review ed, they show inconsistent results.
Roberts and Law rie (1974) and Hsieh et al. (1980) showed that
m icrow ave cookery caused less physical damage to m yofibrillar tissues
as a consequence o f either low er cooking tem peratures of the oven or
snorter cooking tim es being required to reach the same internal
tem perature than by conventional cooking methods.
H utton et al.
(1981) show ed that significant differences were caused by the end
point tem perature, not by conventional and m icrow ave heating.
Some
differences for the characteristics between cooking m ethods in the oven
treatm ents occurred betw een 60° and 70°C.
At 70°C, m icrow ave
sam ples w ere m ore fragm ented, flattened, and coagulated than the
conventional samples.
Cham bers et al. (1982) did not show any
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significant difference in histological characteristics of bovine m uscle
cooked by dry or m oist heat in a conventional or microwave oven.
In
the present study, there is no difference in sarcom ere Form A
appearance of m uscle cooked with different m icrow ave pow er levels.
And at 60 and 70°C, thin and thick fiiam ent were well preserved, but at
80°C, those began to coagulate.
Although TEM studies o f ultrastruetural changes in m eat during
microwave or other heating processes may provide insight into overall
alterations in sarcom eres, they cannot be regarded as a reliable means
of gathering quantitative inform ation.
Light microscopy can be used to
examine sarcom ere length and structure.
Sarcom ere length
m easurem ents in TEM m icrographs may give representative values, but
many replications could be necessary for comparisons of cooking effects.
The results of the light and electron m icroscope studies of
m icrow ave heated roasts indicate that there is considerable variation in
the ultrastructure o f a single muscle.
D ifferent sarcom ere form s and
lengths are apparent in cooked roasts.
This study shows that there are
several sarcom ere forms in SM muscle.
If the same sarcom ere form is
exam ined after heating to different internal tem perature or by different
microwave energy levels, changes appear to be minimal.
In all m eat m uscle, Form A sarcomeres represents a large
proportion of the total.
internal tem peratures.
forms than at 60°C.
The proportion decreases with increasing
A t 70°C and 80°C, there are more sarcom ere
The form s present at the higher internal
tem peratures show greater disintegration and denaturation o f protein
structures than at low er tem peratures.
Ill
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Figure 9.
Light micrograph of longitudinal appearance of raw SM
muscle (58x).
Figure 10. TEM m icrograph o f three types o f sarcom eres (Type A, B
and C) found in raw SM m uscle (5,100x).
mam
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Figure 13. TEM micrograph of Type B sarcomere of raw SM muscle
(17,760x).
Figure 14. TEM micrograph o f Type C sarcom ere of raw SM muscle
(1 7 ,7 6 0 x ).
114
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Figure 15. TEM micrograph of Type D sarcomere found in frozen,
thawed bovine SM muscle (17,760x).
F igure 16. L ight m icrograph o f longitudinal appearance of m uscle
fibers cooked to 60°C with 40% m icrow ave pow er (58x).
11 5
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F igure 17. L ight m icrograph o f longitudinal appearance o f m uscle
fibers cooked to 60°C w ith 60% m icrow ave pow er (58x)
Figure 18. Light m icrograph o f longitudinal appearance o f m uscle
fibers cooked to 60°C with 100% microwave pow er (58x)
116
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Figure 19. L ight m icrograph of longitudinal appearance of m uscle
fibers cooked to 70°C w ith 40% microwave pow er (144x).
Figure 20. Light m icrograph o f longitudinal appearance o f m uscle
fibers cooked to 80°C with 100% m icrow ave power (144x).
117
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Figure 21. Light micrograph of longitudinal appearance of muscle
fibers cooked to 80°C with 100% microwave power, which
was taken from the hardened outer surface of roast (58x).
F igure 22. TEM m icrograph o f tw o Types of sarcom eres (Type A and
B) o f m uscle cooked to 60°C with 40% m icrow ave pow er
(5 ,1 0 0 x ).
118
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Figure 23. TEM micrograph of two types of sarcomeres (Type A and F)
of muscle cooked to 60°C with 40% microwave power (17,760x).
Figure 24. TEM m icrograph o f Type A sarcomere of m uscle cooked
to 60°C w ith 40% m icrow ave pow er (17,760x).
119
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Figure 25. TEM micrograph of Type B sarcomere of muscle cooked
to 60°C with 40% microwave power (17,760x).
Figure 26. TEM m icrograph o f Type F sarcom ere of m uscle cooked
to 60°C with 40% m icrow ave pow er (17,760x).
120
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Figure 27. TEM micrograph of two types of sarcomeres (Type A and B)
of muscle cooked to 60°C with 60% microwave power
(17,760x).
Figure 28. TEM micrograph o f Type A sarcom ere of m uscle cooked
to 60°C with 60% m icrow ave pow er (17,760x).
121
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Figure 29. TEM micrograph of Type B sarcomere of muscle cooked
to 60°C with 60% microwave power (17,760x).
Figure 30. TEM m icrograph o f Type A sarcomere of m uscle cooked
to 60°C with 100% microwave pow er (17,760x).
122
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Figure 31. TEM micrograph of Type B sarcomere of muscle cooked
to 60°C with 100% microwave power (17,760x).
Figure 32. TEM micrograph o f Type E sarcom ere of muscle cooked
to 60°C with 100% m icrowave pow er (17,760x).
1 23
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Figure 33. TEM micrograph of Type A sarcomere of muscle cooked
to 70°C with 40% microwave power (17,760x).
Figure 34. TEM m icrograph o f Type E sarcom ere o f muscle cooked
to 70°C with 40% microwave pow er (17,760x).
124
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Figure 35. TEM micrograph of Type F sarcomere of muscle cooked to
70°C with 40% microwave power (17,760x).
Figure 36. TEM micrograph o f Type G sarcom ere of m uscle cooked to
70°C with 40% m icrow ave power (17,760x).
125
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Figure 37. TEM micrograph of two types of sarcomeres (Type A and F)
o f muscle cooked to 70°C with 60% microwave power
Figure 38. TEM micrograph o f Type B sarcom ere of muscle cooked
to 70°C with 60% m icrowave pow er (17,760x).
126
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Figure 39. TEM micrograph of Type D sarcomere of muscle cooked
to 70°C with 60% microwave power (17,760x).
F igure ^0. TEM m icrograph o f Type F sarcom ere of m uscle cooked
to 70°C with 60% m icrowave pow er (I7,760x).
127
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Figure 41. TEM micrograph of Type G sarcomere of muscle cooked
to 70°C with 60% microwave power (17,760x).
Figure 42. TEM micrograph o f Type A sarcomere of m uscle cooked
to 70°C with 100% m icrow ave pow er (17,760x).
128
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Figure 43. TEM micrograph of contracted Type F sarcomere of muscle
cooked to 70°C with 100% microwave power (17,760x).
Figure 44. TEM micrograph of Type F sarcomere of m uscle cooked
to 70°C with 100% m icrow ave power (17,760x).
129
R ep ro d u ced with p erm ission of th e copyright ow ner. Further reproduction prohibited w ithout p erm ission .
Figure 45. TEM micrograph of Type E sarcomere of muscle cooked
to 70°C with 100% microwave power (17,760x).
Figure 46. TEM micrograph o f Type A sarcom ere of m uscle cooked
to 80°C with 40% microwave pow er (17,760x).
130
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Figure 47. TEM micrograph of Type A sarcomere of muscle cooked
to 80°C with 60% microwave power (17,760x).
Figure 48. TEM micrograph o f Type E sarcom ere o f m uscle cooked
to 80°C with 60% m icrowave pow er (17,760x).
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
H g u re 49. TEM micrograph of T
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Figure 50. TEM m,-„
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Figure 51. TEM micrograph of Type A sarcomere of muscle cooked
to 80°C with 100% microwave power (17,760x).
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Figure 52. TEM m icrograph of contracted Type F sarcom ere of m uscle
cooked to 80°C with 100% m icrowave pow er (17,760x).
13 3
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Figure 53. TEM micrograph of Type F sarcomere of muscle cooked
to 80°C with 100% microwave power (17,760x).
134
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Table 26.
Type
Different sarcomere types found in raw and SM muscle
cooked to 60°C.
60°C-4Q%
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Table 27. Different sarcomere types found in SM muscle cooked to 70°C.
Type
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Table 28. Different sarcomere types found in SM muscle cooked to 80°C.
Type
80°C-40%
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S
Chapter 6
U ltr a s tr u c tu r a l
S e m im e m b ra n o s u s
C hanges
M u scle
o f C o llag en
D u rin g
of
B ovine
M ic ro w a v e
H e a tin g
In tro d u c tio n
Collagen is an im portant com ponent of the connective tissue in
muscle that affects the tenderness of cooked meat.
The
characteristics of collagen during cooking has been investigated in a
num ber o f studies by chem ical and physical methods.
In several
reports, light or scanning electron m icroscopy was used to exam ine
the structure o f collagenous m aterial.
The objective of this study was to investigate the
ultrastructural changes of collagen tissue of sem im em branosus (SM)
beef m uscle cooked to three different internal tem peratures (60, 70,
80°C) with three different power levels (40, 60, 100%) by using
transm ission electron m icroscopy.
M a te r ia ls
ana
m e th o d s
The experim ental procedures are given in Chapter 5.
Figures
54 to 102 are at the end of Chapter 6.
R e s u lts
and
d is c u s s io n
Light m icrographs of m uscle stained for collagen were taken
for all treatm ent.
Electron m icrographs w hich show ed perim ysium
and endom ysium were identified and included here.
H owever, some
138
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treatm ents are not represented because sam ple blocks for electron
m icroscopy did not contain appropriate sections.
E n d o m y siu m
Figures 54 to 64 are light m icrographs of endom ysium in
bovine raw and cooked bovine SM m uscles.
The spaces between
endom ysium and m uscle fibers cooked to 60 and 70°C are greater
than those cooked to 80°C.
This is especially evident in the hardened
outer surface of m uscle cooked to 80°C, which is shown in Figure 64,
show ing sm aller spaces betw een m uscle fibers an d endom ysium .
This trend is sim ilar to the m odel of the sequential shrinkage events
in m eat during cooking, which was proposed by Sim s and Bailey
(1982).
T heir m odel shows that only m uscle fiber shrinks at 45-50°C
and endom ysium shrinks at 65-80°C, therefore, the space is reduced
when the endom ysium shrinks.
The light m icrographs (Figure 58
and 59) also show granulation of collagen during heating.
Figure 65 shows a TEM micrographs of endom ysium of raw SM
m uscle.
Endom ysium o f raw m uscle shows an open tubular
appearance, through w hich fine collagen fibers m ake a discontinuous
net work.
Figures 66 to 71 show endom ysium of SM m uscle cooked
to 60 and 70°C w ith three different microw ave pow er levels.
W hen
endom ysium is heated to 60°C with 40% m icrow ave pow er levels, the
fine fibrous tube is still seen.
However, in endom ysium heated to 60
and 70°C w ith 60 and 100% m icrowave pow er levels, the fibrous
tubes are shrunken.
G ranular deposits can be seen on the netw ork, but may not be
denatured collagen.
Instead, this granular m aterial may result from
139
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the solubilization of sarcolem m a m aterials as described by Rowe
(1 9 8 9 b )
Jones et al. (1977) and W u e t al. (1985) showed ultrastructural
changes o f endom ysial collagen during heating by using SEM.
They
showed that endom ysial collagen lost its fibrous appearance at 60°C.
Schm idt and P arrish (1971) observed that endom ysial connective
tissue shrinkage was initiated at 50°C and it was com pleted at
approxim ately 70°C.
TEM m icrographs showing endom ysial collagen
were presented by Rowe (1989b).
He showed that the real
appearance of heat denatured collagen m ight be thickened,
unravelled
fib rils.
The structural changes o f endom ysial collagen upon heating
m ight be different for the different types of collagen fibers.
From
the electron m icrographs seen in the present study, the fibrous open
tube of endom ysium is collapsed during heating.
Collagen and elastin in bovine SM muscle
Figures 72 to 91 show perim ysial collagen w ith light
m icrographs.
Collagen, which stains red, and elastin, which stains
black are easily distinguished under the light m icroscope directly.
However, it is difficult to distinguish elastin from collagen in the
black and w hite light micrographs.
In these sam ples, the elastin
fiber in SM m uscle was rarely found in the perim ysium , but many
thin elastin fibers were found around the blood vessels through all
raw and cooked SM muscles.
The elastin found in perimysium was
buried in the bundles o f collagen and had small irregular shapes.
140
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This kind of distribution o f elastin and collagen was also found in
bovine LD m uscle in the study o f Venable (1963).
Bendall (1967)
showed that LD and SM muscle had low elastin content.
Therefore, it
is believed that distribution o f elastin and collagen in SM m uscle may
be similar to that of LD muscle.
However, Rowe (1986) showed lots
of coarse elastin fibers in ST and lots of finer elastin fibers in LD
muscle.
ST m uscle was found to have higher elastin content than
other muscles in the study of Bendall (1967).
P e rim y s iu m
Figures 72 to 91 show the appearance of perim ysial collagen in
SM muscle heated w ith different conditions in light m icrographs.
H eavy deposits of perim ysial collagen w ere found betw een m uscle
bundles through all light m icrographs.
has an appearance like threads.
Perim ysial collagen usually
B ut other forms o f perim ysial
collagen were found in SM m uscle.
Light (1987) m entioned that the
perim ysium was generally characterized by very high quantities of
fibrous collagen w ith only residual am ounts of noncollagenous
muscle protein.
In this study, an effort was made to see the changes
o f heavily concentrated perim ysial collagen found in SM m uscle.
The
perim ysial collagen heated to 60°C with 40% m icrow ave pow er levels
did not change after heating (Figures 74 and 75).
However, the
perim ysial collagen did change in appearance in m uscles at other
internal tem peratures and other m icrow ave pow er levels, show ing
congealed or gelatinized collagen (Figures 76 to 91).
It can also be
seen that the solubilized m aterial spreads betw een m uscle fibers
141
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(Figure 82).
H ow ever, it is difficult to tell from the light micrographs
w hether the degrees o f gelatinization of perim ysial collagen are
different at d ifferen t treatm ents.
Schm idt and P arrish (1971) chose
a less concentrated perim ysial collagen area to see heat changes and
reported th at they observed shrinkage and fragm entation of
perim ysial connective tissue at 60°C.
W hen the appearance of
perim ysial collagen in the present study is com pared to that study, a
sim ilar situation is found.
However, when a large aggregation of
perim ysial collagen w as observed in current study, shrinkage and
fragm entation w ere not seen, but congealed and gelatinized collagen
w ere
o bserved.
Figures 92 to 102 show electron m icrographs of collagen of raw
and cooked SM m uscles, which contain heavy deposits of perim ysial
collagen.
The electron m icrographs are consistent with the light
micrographs.
P erim ysial collagen of SM m uscle cooked to internal
tem perature o f 60°C w ith 40% m icrow ave pow er level (Figure 93)
began to gelatinize in only a small area o f collagen fibers, and looked
like thickened, unravelled fibrils as shown in the study o f Rowe
(1989).
fibers.
B ut m ost areas o f perim ysial collagen had intact collagen
As m icrow ave pow er levels w ere increased, the area of
gelatinized perim y sial collagen was increased at 60°C internal
tem perature (Figures 94 to 96).
A t 70°C, m ost areas of perim ysial
collagen have a g elatinized appearance and as tem perature
increased, the d iam eter of gelatinized collagen fibers increased
(Figures 97 to 99).
D ifferences between m icrow ave pow er levels at
tem peratures of 70°C and over w ere not detected (Figures 97 to
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The fibrous appearance of perim ysial collagen is still discerned at
80°C.
Because transm ission electron m icrographs of collagen fibers
are rarely seen in reports, com parison with other research is not
possible.
By using SEM, Hutton et al. (1981) showed significant
changes in collagen between 40° and 50°C.
They m entioned that
collagen was more affected in the microwave oven than in the
conventional oven, which is in contrast with the study of Hsieh et al.
(1980).
However, W u et al. (1985) showed that endom ysium and
perim ysium becam e granular at 60°C and gelatinized at 80°C.
From
the electron m icrographs in the current study, it seems that collagen
begins to gelatinize in parts at 60°C and most collagen fibers
gelatinize over 70°C.
W hen the present results are com pared w ith
other results, it is believed that changes of perim ysial collagen are
related to internal tem perature of the m eat rather than oven type.
W hen the TEM m icrographs are com pared with the collagen
solubility data, shown in Table 23 in Chapter 4, percentage of
collagen solubility at 60°C (about 20%) is lower than at 70 and 80°C
(about 25%).
Collagen solubility at 70 and 80°C is com parable.
H owever, electron m icrographs o f perim ysial collagen show that only
small areas at 60°C and large areas at 70 and 80°C had solubilized.
It
is possible that at 60°C, collagen fibers are ready to solubilize, even
though the structure o f collagen fiber looks intact in TEM
m ic ro g ra p h s.
143
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Figure 54. Light micrograph of endomysium and perimysium of
raw SM muscle (144x).
Figure 55. Light m icrograph o f endomysium of SM m uscle cooked
to 60°C with 40% microwave pow er (144x).
144
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Figure 56. Light micrograph of endomysium of SM muscle cooked
to 60°C with 60% microwave power (144x).
9.
$
Figure 57. Light m icrograph o f endom ysium of SM m uscle cooked
to 60°C with 100% m icrow ave pow er (144x).
145
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Figure 58. Light micrograph of endomysium and perimysium of SM
muscle cooked to 70°C with 40% microwave power (144x).
Figure 59. Light m icrograph o f endom ysium and perim ysium o f SM
muscle cooked to 70°C with 60% m icrow ave pow er (144x).
146
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Figure 60. Light micrograph of endomysium of SM muscle cooked
to 70°C with 100% microwave power (58x).
Figure 61. Light m icrograph o f endom ysium o f SM m uscle cooked
to 80°C with 40% m icrow ave pow er (144x).
m
i
147
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Figure 62. Light micrograph of endomysium of SM muscle cooked
to 80°C with 60% microwave power (144x).
F igure 63. L ight m icrograph of endom ysium of SM m uscle cooked
to 80°C with 100% microwave pow er (144x).
148
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Figure 64. Light micrograph of endomysium of outer surface of SM
muscle cooked to 80°C with 100% microwave power (58x).
Figure 65. TEM m icrograph o f endom ysium o f raw SM m uscle
(6 ,6 0 0 x ).
149
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Figure 66, TEM micrograph of endomysium of SM muscle cooked
to 60°C with 40% microwave power (10,560x).
Figure 67. TEM m icrograph o f endom ysium of SM m uscle cooked
to 60°C with 60% m icrow ave pow er (10,560x).
150
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Figure 68. TEM micrograph of endomysium of SM muscle cooked
to 60°C with 100% microwave power (10,560x).
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Figure 69. TEM m icrograph of endom ysium of SM m uscle cooked
to 70°C with 40% m icrowave power (10,560x).
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151
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Figure 70. TEM micrograph of endomysium of SM muscle cooked to
70°C with 60% microwave power (10,560x).
Figure 71. TEM m icrograph o f endomysium of SM m uscle cooked to
70°C with 100% m icrowave power (10,560x).
152
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Figure 72. Light micrograph of perimysial collagen of raw SM
muscle (58x).
Figure 73. Light m icrograph o f perim ysial collagen o f raw SM
m uscle (580x).
153
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Figure 74. Light micrograph of perimysial collagen of SM muscle
cooked to 60°C with 40% microwave power (58x).
Figure 75. L ight m icrograph o f perim ysial collagen of SM m uscle
cooked to 60°C w ith 40% m icrow ave pow er (580x).
154
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Figure 76. Light micrograph of perimysial collagen of SM muscle
cooked to 60°C with 60% microwave power (144x).
Figure 77. Light m icrograph o f perim ysial collagen of SM m uscle
cooked to 60°C with 60% m icrowave pow er (580x).
155
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Figure 78. Light micrograph of perimysial collagen of SM muscle
cooked to 60°C with 100% microwave power (58x).
Figure 79. L ight micrograph o f perim ysial collagen of SM muscle
cooked to 60°C with 100% m icrow ave power (580x).
156
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Figure 80. Light micrograph of perimysial collagen of SM muscle
cooked to 70°C with 40% microwave power (58x).
i
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f
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Figure 81. Light m icrograph of perim ysial collagen of SM muscle
cooked to 70°C with 40% m icrow ave pow er (580x).
157
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Figure 82. Light micrograph of perimysial collagen of SM muscle
cooked to 70°C with 60% microwave power (58x).
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Figure 83. Light m icrograph o f perim ysial collagen of SM muscle
cooked to 0°C with 60% microwave pow er (580x).
158
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
Figure 84. Light micrograph of perimysial collagen of SM muscle
cooked to 70°C with 100% microwave power (58x).
Figure 85. Light m icrograph o f perimysial collagen of SM muscle
cooked to 70°C with 100% m icrow ave pow er (580x).
15 9
R ep ro d u ced with p erm ission o f the copyright ow ner. Further reproduction prohibited w ithout p erm ission.
Figure 86. Light micrograph of perimysial collagen of SM muscle
cooked to 80°C with 40% microwave power (58x).
Figure 87. Light m icrograph o f perim ysial collagen of SM m uscle
cooked to 80°C with 40% microwave power (580x).
160
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Figure 88. Light micrograph of perimysial collagen of SM muscle
cooked to 80°C with 60% microwave power (58x).
Figure 89. Light m icrograph o f perimysial collagen of SM m uscle
cooked to 80°C with 60% microwave pow er (58x).
161
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Figure 90. Light micrograph of perimysial collagen of SM muscle
cooked to 80°C with 100% microwave power (58x).
Figure 91. Light m icrograph o f perim ysial collagen of SM m uscle
cooked to 80°C with 100% microwave pow er (580x).
162
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Figure 92. TEM micrograph of perimysial collagen of raw SM muscle
(17,760x).
•t;
Figure
. TEM m icrograph o f perim ysial collagen o f SM muscle
cooked to 60°C with 40% m icrow ave pow er (17,760x).
163
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Figure 94. TEM micrograph of perimysial collagen of SM muscle
cooked to 60°C with 60% microwave power (17,760x).
F igure 95. TEM m icrograph o f perim ysial collagen of SM m uscle
cooked to 60°C with 100% m icrowave pow er (17,760x).
164
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Figure 96. TEM micrograph of perimysial collagen c f SM muscle
cooked to 60°C with 100% microwave power (17,760x).
Figure 97. TEM m icrograph o f perim ysial collagen of SM muscle
cooked to 70°C w ith 40% m icrow ave pow er (I7,760x).
165
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Figure 98. TEM micrograph of perimysial collagen of SM muscle
cooked to 70°C with 60% microwave power (17,760x).
F igure 99. TEM micrograph o f perim ysial collagen of SM muscle
cooked to 70°C with 100% m icrow ave pow er (17,760x).
• f
166
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Figure 100. TEM micrograph of perimysial collagen of SM muscle
cooked to 80°C with 40% microwave power (17,760x).
F ig u re 101. TEM m icrograph o f perim ysial collagen o f SM m uscle
cooked to 80°C w ith 60% m icrow ave pow er (17,760x).
167
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Figure 102. TEM micrograph of perimysial collagen of SM muscle
cooked to 80°C with 100% microwave power (17,760x).
168
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Chapter 7
Sum m ary
The objectives o f this study were to (1) determ ine the effects
of different m eat m asses on m icrowave oven efficiency, chem ical and
physical characteristics o f sem im em branosus beef (SM ) m uscle roasts
cooked by m icrow ave heating, and (2) the effects of m icrow ave
pow er levels and final internal endpoint tem perature on chem ical,
physical and histological characteristics of SM beef m uscle roasts.
Four different meat masses (100, 500, 1000, 1500g) of SM
roasts w ere cooked by m icrow ave energy to an internal tem perature
of 70°C using three different microwave power levels (40, 60, 100%).
Also, SM roasts (1500g) were cooked by microwave heating to three
different internal tem peratures (60, 70, 80°C) using three different
microwave power levels (40, 60, 100%).
Cooking time, standing time,
post processing tem perature rise (PPTR), m oisture, fat, protein,
thiam in content and retention, and percent solubilized collagen were
determ ined.
Machine.
Texture was m easured by the Instron U niversal Testing
W ater holding capacity (WHC) was determ ined using a
press m ethod.
L ight and transm ission electron m icroscopy were
used to exam ine ultrastructural changes of m yofibrillar and collagen
tissu e s.
The perform ance of the m icrowave oven was tested.
The
microwave oven used in the present study had a 13 second tim e
base and 700 w atts nom inal power.
The m easured pow er output, as
percentage of full power, was higher than the expected m icrow ave
169
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pow er level.
Load factor tests with water and meat of different
m asses were done.
W hen water mass was increased, the efficiency
of the oven also increased.
The more w ater in the microwave oven,
the m ore efficient the heating, i.e., more o f the available microwave
energy was absorbed.
However, the efficiency of the oven was
decreased as m eat m ass was increased at all different m icrow ave
power levels.
The actual power output w ould vary for different food
items because of the difference in specific heat of food items.
Therefore, food mass and specific heat should be considered to obtain
a desirable final product by m icrowave heating.
Cooking tim es per kg for different m eat masses were
significantly different when 40 and 60% m icrow ave pow er levels
were used for m icrow ave cooking, but not at 100% power.
times per kg w ere least for the smallest m eat size.
Cooking
W hen the
differences in cooking time per unit of w eight for different meat
m asses are considered, estim ations of cooking tim e should account
for ro ast size.
Results o f this study indicate that approxim ately 10°C
tem perature rise can be expected in 1.5 kg beef roasts after they are
rem oved from the m icrow ave oven.
The roasts reached the final
internal endpoint tem perature approxim ately 10 to 15 m inutes after
rem oval from th e oven.
Recomm endations foT micTowave meat
preparation, th erefo re, should include instructions regarding
standing tim e an d tem perature rise after cooking.
There w ere no significant differences in total losses for all meat
m asses and m icrow ave pow er levels.
However, drip losses decreased
as m eat m asses increased, and evaporation losses increased* as m eat
170
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m asses increased.
M ore evaporation of drippings occurred during
the longer cooking tim e needed for larger meat masses.
There was no significant interaction between m eat m ass and
m icrow ave pow er levels for all m easured characteristics o f roasts.
M oisture, protein, W HC, thiam in content and retention did not differ
significantly among cooking treatm ents or m eat m asses.
There was
an increasing trend in fat content as meat masses increased.
Larger
roasts have m ore interm uscular fat, so sampling may include more
fat.
Instron m easurem ent show ed no consistent trend am ong all
treatm ents, although shear values tended to decrease as pow er level
increased.
Solubilized collagen was measured for all treatm ents.
There was an increasing trend in percent solubilized collagen as meat
mass increased, probably due to the longer cooking time..
There was
no correlatio n betw een Instron tenderness m easurem ents and
percent solubilized collagen.
Cooking tim es for roasts (1.5 kg) cooked to three internal
endpoint tem peratures w ith three different m icrow ave pow er levels
were significantly different.
As expected, cooking times per kg were
longer for roasts cooked to higher internal tem peratures.
F or each
internal tem perature, cooking tim es per kg were significantly shorter
at the higher pow er levels.
PPTR ranged from 9 to 18°C.
In general,
beef roasts should be taken out at least 10°C below the desired
internal tem perature and allow ed to stand for at least 15 m in to
reach the desired internal tem perature, based on the findings of this
s t ud y.
171
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There was a significant difference in total losses of roasts
cooked to the three differen t internal endpoint tem peratures, with
80°C roasts having greatest losses.
At 60°C, total losses tended to
increase as m icrowave pow er level was increased.
But there was no
difference in total losses for 70 and 80°C at different microwave
power levels.
An evaporation ratio was calculated by dividing
evaporation losses by total losses.
The evaporation ratio tended to
increase as m icrow ave pow er level and internal tem perature
increased.
Total losses o f 60°C roasts cooked with m icrowaves in the
present study seem ed to be much larger than those prepared by
conventional heating in other studies.
This may be attributed to
greater evaporation from the unbrowned surface of the roasts.
However, total losses of 70 and 80°C roasts in the present study were
sim ilar to other studies.
M oisture and protein content were significantly different
among roasts cooked to the different internal tem peratures.
content was inversely related to m oisture content.
not significantly different am ong all treatments.
Protein
Fat content was
W HC show ed a
decreasing trend as pow er level and internal tem peratures w ere
increased.
Thiam in content and retention showed significant
differences at different internal tem perature.
At 80°C, thiam in
content and retention was m uch lower than in the 60 and 70°C
roasts.
There was no significant difference in thiam in content and
retention among roasts cooked at different pow er levels.
Instron m easurem ents o f texture showed inconsistent trends
among all treatm ents and few significant differences.
Only
172
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com pression springiness differed among treatm ents.
H ow ever, the
values for com pression springiness are so small, the differences are
probably not im portant.
Percent solubilized collagen tended to increase as internal
tem perature increased.
Percent solubilized collagen of roasts at 70
and 80°C was similar, and higher than that of 60°C roasts.
This might
reflect the transition tem perature for collagen solubilization.
Collagen solubility and Instron tenderness m easurem ents w ere not
c o rre la te d ,
TEM m icrographs of m yofibrillar tissue from roasts cooked to
d ifferent internal tem peratures with different m icrow ave pow er
levels show the presence o f several different sarcom ere form s in
sam e treatm ent.
Sarcom ere forms were classified according to the
structural characteristics visible in the micrographs.
It is difficult to
say that these different sarcom ere forms were due to different heat
treatm ent.
W hen com paring Form A sarcom ere only w ith different
treatm ents, there was decreasing trend in sarcom ere length as
tem perature and pow er level was increased.
As internal
tem perature of roasts was increased, the sarcom ere form s becam e
m ore denaturated and lost their identities.
D ifferent form s of
sarcom eres had quite different sarcom ere lengths.
Structural changes o f endomysium were detected in 60 and
70°C roasts.
TEM micrographs suggested that the transition
tem perature of collagen solubilization might be between 60 and 70°C.
The fine network o f endom ysium became shrunken as internal
tem p eratu re
in creased .
17 3
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There were some difficulties in observing structural changes of
perim ysium under the electron m icroscope.
did not have any perim ysium m aterial.
Sometimes the section
Small areas of denatured
structure of perimysium were seen in TEM micrographs of 60°C
roasts, and as tem perature increased, the area of denatured structure
e n la rg e d .
The use of variable pow er for microwave cooking of beef roasts
does not result in m easurably different chem ical or physical
characteristics.
H istological exam ination of the ultrastructure of
m uscle and collagen revealed changes in sarcom ere appearance and
size.
The effects of different internal endpoint tem peratures appear
to be as great or greater than those of power levels.
Recom m endations for m icrow ave cooking of m eat should take into
account m eat m ass, desired endpoint tem perature, and post-cooking
tem p eratu re
rise.
174
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Vita
Kyunghee Cho Lee was bom on M arch 2, 1955 in Seoul, Korea.
She graduated from Ew ha Girl's High School in 1974.
She received a
Bachelor of Science degree in Foods and N utrition in 1978.
She
worked as a researcher in the Food Technology Laboratory of Korea
Institute o f Science and Technology for two years.
She earned her
M.Ag. degree in the Departm ent of Food Technology of Korea
University in 1982.
She was a part time lecturer in Shin-Gu Junior
College until she cam e U nited States in 1984 with her husband and
son.
In 1986, she entered the graduate program in the D ivison of
Foods and N utrition at the University of Illinois.
186
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