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J Sci Food Agric 1998, 77, 387È392
The Effect of Green Ham pH and NaCl
Concentration on Cathepsin Activities and the
Sensory Characteristics of Dry-cured Hams
Jacint Arnau,* Luis Guerrero and Carmen Sa rraga
Institut de Recerca i Tecnologia Agroalimentàries (IRTA), Centre de Tecnologia de la Carn, Granja Camps
i Armet, 17121-Monells, Girona, Spain
(Received 17 January 1997 ; revised version received 17 July 1997 ; accepted 20 November 1997)
Abstract : There is a tendency to reduce the amount of NaCl in the manufacturing process of Spanish dry-cured ham. NaCl, pH and temperature determine
the stability of this product. This study was concerned with the evaluation of
green ham pH and sodium chloride concentration on cathepsin activities,
physico-chemical parameters and sensory characteristics of dry-cured hams. Two
di†erent amounts of salt (55 and 80 g kg~1) and two di†erent pH levels (pH at
24 h post mortem \5É8 ; pH at 24 h post mortem [6É2) were used. Physicochemical composition, cathepsin activity and a number of sensory parameters
were evaluated. Hams with high pH displayed lower cathepsin activity, NPN,
saltiness and hardness whereas the levels of brightness, crumbliness, pastiness
and adhesivity were found to be higher than in normal hams. A high level of salt
produced greater cathepsin B and B ] L activity and lower pastiness and adhesivity than the samples with a low NaCl level. ( 1998 SCI.
J Sci Food Agric 77, 387È392 (1998)
Key words : pH ; salt ; cathepsins ; sensory properties ; dry-cured ham
into dry cured ham should be pH \ 6É2. A high pH
24
24
also favours the formation of phosphate crystals (Arnau
et al 1993) which can lower the level of consumer acceptance. Recent studies have shown an incidence of green
hams with pH [ 6É2 from 5É4 to 12É5% in Spain
24
(Guerrero et al 1991 ; Garrido et al 1994). This kind of
meat has less appropriate sensory and technological
characteristics for the production of dry-cured ham
than normal meat (Poma 1991).
Texture is one of the sensory factors determining food
acceptability. The soft and pasty texture sometimes
found in dry-cured hams makes slicing more difficult
and produces a mouthcoating sensation which could
a†ect consumer acceptability (Arnau 1991). Parolari et
al (1988) reported that softness is favoured by both high
levels of intramuscular fat and low salt to moisture
ratios, in particular when the cold-resting periods are
short. The texture parameter is also a†ected by the temperature of the process and, of course, the characteristics of the meat itself (Parolari et al 1994 ; Gou et al
1995 ; Virgili et al 1995 ; Guerrero et al 1996 ; Arnau et
al 1997a).
INTRODUCTION
The industrial processes used in the manufacture of drycured hams are based on traditional methods which rely
mainly on the addition of NaCl and the dehydration
process. At present, there is a general tendency to
reduce the sodium content in foods. However, NaCl
reduction in dry-cured ham can a†ect its stability and
its typical sensory characteristics (Parolari et al 1988 ;
Arnau 1991).
pH is a fundamental parameter in the evaluation of
meat quality and, together with water activity and temperature, it is one of the main factors determining the
microbiological stability of the ham (Leistner 1985).
Newton and Gill (1981) reported that meat with a high
pH is prone to deterioration because of the low level of
glucose and intermediate glycolitic compounds present
in it. According to Poma (1980), the maximum value for
pH at 24 h (pH ) post mortem for meat transformation
24
* To whom correspondence should be addressed.
Contract/grant sponsor : INIA.
Contract/grant number : Sc93-126.
387
( 1998 SCI.
J Sci Food Agric 0022È5142/98/$17.50.
Printed in Great Britain
J Arnau, L Guerrero, C Sa rraga
388
Previous studies on the role of muscle proteinases in
cured ham have suggested that cathepsins are one of the
factors responsible for proteolysis during ageing, since
their activity is maintained throughout the process (Gil
et al 1991 ; Parren8 o et al 1994) whereas calpain activity
is not detected after the post-salting stage (Sarraga et al
1993). Parolari et al (1994) suggested the use of raw hams
with a low level of cathepsin B activity in order to
improve the texture and the quality of the product.
The aim of this paper is to study the e†ect of green
ham pH and sodium chloride concentration on cathepsin (EC numbers : BÈ3.4.22.1 ; LÈ3.4.22.15 ; DÈ
3.4.23.5) activities and the texture characteristics of
Spanish dry-cured hams aged for 6 months.
MATERIAL AND METHODS
Raw material
Gilt carcasses from a commercial slaughterhouse were
selected according to pH and conductivity. pH was
measured at 45 min (pH ) and 24 h post mortem (pH )
45
24
with a combined electrode (Ingold 406, Ingold, Urdorf,
Switzerland) attached to a portable pH-meter (Crison
507, Crison Instruments SA, Barcelona, Spain). Electrical conductivity was measured with a quality-meter
(Tecpro) at 24 h post mortem (Swatland 1980). Both pH
and conductivity were measured in the Semimembranosus muscle. Hams weighing between 9 and
10 kg with pH [ 6É0 and conductivity \6 lS were
45
selected. At 24 h post mortem the hams were divided
into two groups according to their pH levels : pH [
24
6É2 (HpH) and pH \ 5É8 (LpH).
24
Processing and sampling
The hams were Ðrst treated with 0É8 g of KNO kg~1
3
and randomly assigned to two di†erent salting procedures : 6 hams were salted with 80 g of sodium chloride kg~1 of ham (batch 1) and 6 hams with 55 g kg~1
of ham (batch 2) in each group of selected pH. After salt
absorption they were hung for 35 days at 4¡C and
80È90% RH. During the ageing process the hams were
stored at 12È16¡C for 4 months and then at 24¡C (65È
85% RH) for 1 month.
All the tests were carried out at the end of the process
on the Biceps femoris muscle. A 100 g sample from each
ham, sliced perpendicular to the femur from the middle
of the Biceps femoris muscle, was used for chemical
analysis.
Physicochemical analysis
Weight loss was determined at the end of the process
with reference to the initial weight. The following
analyses were carried out on each sample : ground meat
pH, moisture as weight loss at 103 ^ 2¡C (Presidencia
del Gobierno 1979), total protein (N ] 6É25) (Kjeldahl
method) (Presidencia del Gobierno 1979), NaCl by the
Charpentier-Volhard method (ISO 1970), phosphate
determination (Presidencia del Gobierno 1979), tyrosine
(Tyr) (Pearson 1968) and non-protein nitrogen (NPN)
(Keresse 1984).
Extraction of lysosomal enzymes
Lysosomal enzymes were extracted according to the
method of Etherington et al (1990) in which a portion of
ground muscle was homogenised in four parts (w/v) of
ice-cold 50 mM sodium acetate bu†er, pH 5É0, containing 1 mM EDTA and 0É2% Triton ] 100. The extract
was stirred for 1 h at 4¡C and then centrifuged
(10 000 ] g). The supernate was Ðltered to remove the
debris and used as the source of cathepsins.
Protein concentration of the enzyme extracts was
determined by the method of Lowry et al (1951) using
bovine serum albumin as standard.
Assay of enzyme activities
Cystein proteinases B and L were determined Ñuorimetrically using the method of Etherington and
Wardale (1982). Cathepsin B and L were assayed with
the common substrate N-CBZ-L-phenylalanyl-L-arginine 7-amido-4-methylcoumarin (Z-Phe-Arg-NHMec)
(Bachem). Cathepsin B was measured with N-CBZ-Larginyl-L-arginine 7-amido-4-methylcoumarin (Z-ArgArg-NHMec) (Bachem). One unit of activity was
deÐned as the amount of enzyme hydrolysing 1 nmol of
substrate min~1 at 37¡C.
Cathepsin D was assayed against denatured bovine
haemoglobin (Sigma) (Etherington 1972) and the TCAsoluble peptides were measured by the method of
Lowry et al (1951) using L-tyrosine as standard. One
unit of activity was deÐned as the amount of enzyme
releasing 1 lg of tyrosine min~1 at 45¡C. SpeciÐc activities were given in enzyme units mg~1 of extracted
protein.
Sensory analysis
Sensory evaluation was carried out by a panel of eight
trained panelists on 2-mm thick slices from the Biceps
femoris muscles. A six-session randomised completeblock design was applied (Steel and Torrie 1980). Each
ham was evaluated by the eight panelists in the same
session and the panel average was recorded. To assess
the hams, the order of presentation and the Ðrst-order
carry-over e†ects were balanced (MacFie et al 1989).
Sensory descriptors were selected from a descriptive
proÐle generated by open discussion between the
members of the panel and technicians working in the
dry-cured ham industry. Brightness, hardness, crumbliness, pastiness, adhesivity and saltiness were evaluated
pH and NaCl concentration in dry-cured hams
389
on a non-structured 10 cm length scale with anchor
points 1 cm from each end, similar to that proposed by
Stone et al (1974), where 0 means absence and 10 means
great intensity. A number of dry-cured hams showing
di†erent intensities were used to deÐne the scale for the
descriptors.
The assessors were selected and trained following
ASTM standards (ASTM 1981). This panel has 7 years
experience in texture proÐle, Ñavour proÐle and the
descriptive analysis of a wide range of foods.
Statistical analysis
The data were analysed using the ANOVA procedure
from SAS (SAS 1987). The model included pH, added
NaCl and their interaction as Ðxed e†ects. The t-test
was used for comparison of means.
RESULTS AND DISCUSSION
Table 1 shows the means and standard errors of the
physico-chemical parameters and cathepsin activities of
hams with di†erent pH levels and amounts of NaCl, as
well as the signiÐcance of the pH ] NaCl interaction.
The number of phosphate crystals on the surface was
greater in the hams with high pH. However, the phosphate amount expressed as P O was lower in the
2 5
Biceps femoris of HpH hams due to greater phosphate
migration to the surface of the ham (Arnau et al 1993).
The P O concentration was not signiÐcantly a†ected
2 5
by the amount of salt ; though the tendency observed
agrees with the results of Arnau et al (1997a).
Even though the HpH hams had a higher surface
rugosity which facilitates dehydration, they registered a
higher moisture content than the LpH hams in the
Biceps femoris muscle (P \ 0É05). This could be due to
the increase of water-holding capacity with pH.
Moisture in batch 1 was lower than in batch 2, possibly due to the higher osmotic dehydration produced by
NaCl.
Cathepsins are lysosomal proteolytic enzymes that
show optimal pH between 4É0 and 5É5 (for reviews see :
Goll et al 1983 ; Zeece and Katoh 1989 ; Ouali 1990 ;
Roncales et al 1995) ; and this could be the reason for
the higher activity rate found in the samples of Biceps
femoris muscle from the LpH hams. The higher content
of NPN and Tyr observed in the LpH hams (Table 1)
suggested that the better cleavage of the myoÐbrilar
structure produced by cathepsins in low meat pH conditions facilitates the action of other enzymes able to
produce small peptides and amino acids.
The hams in batch 1 showed an important increase in
cystein proteinase activities when compared to the hams
in batch 2. These results would conÐrm the idea of the
stabilising e†ect that the salt has on these enzymatic
activities (Toldrà and Etherington 1988). In the LpH
hams the pH ] NaCl interaction displayed a greater
NaCl e†ect on enzyme activity than in HpH hams
(Table 2). NaCl concentration did not a†ect cathepsin
D activity at the end of the process. NaCl facilitates
changes in the myoÐbrilar structure, due to the increase
of osmotic pressure, which favours the accessibility of
myoÐbrilar proteins by proteinases. However, in in vitro
studies, NaCl was found to inhibit protease activities
(Sarraga et al 1989 ; Rico et al 1990). This could explain
TABLE 1
Physico-chemical composition and enzymatic cathepsin activities of Biceps femoris musclesa
pH
24
High
L ow
High level (80b)
L ow level (55b)
Mean
SE
Mean
SE
Mean
SE
Mean
SE
6É58a
632a
258
79É9
5É099b
5É88b
33É3b
0É03
5É9
4É2
4É8
0É117
0É25
0É3
6É08b
613b
266
85É6
5É456a
7É16a
36É1a
0É03
5É3
2É2
5É1
0É093
0É36
0É8
6É34
613b
260
96É1a
5É196
6É45
35É1
0É07
5É3
3É3
2É2
0É131
0É38
0É9
6É32
633a
264
69É4b
5É359
6É59
34É4
0É09
6É2
3É7
3É6
0É099
0É35
0É6
NS
NS
NS
NS
NS
NS
NS
Cathepsin activitiesd
D
0É198b
B
2É9b
B]L
6É8b
0É012
1É13
1É91
0É282a
11a
22a
0É029
3É12
6É84
0É226
12É4a
25É5a
0É018
2É8
6É12
0É254
1É5b
3É3b
0É031
0É87
1É07
NS
**
*
pH
Moistureb
N ] 6É25b
NaClb
P O b
2 5
Tyrosinec
NPNc
a
b
c
d
pH ] NaCl
Added NaCl
Means within pH or added NaCl with di†erent following letters are signiÐcantly di†erent (P \ 0É05).
24
Results are given as g kg~1 of ham.
Results as mg g~1 of N ] 6É25.
Activities are given as units per mg of extracted protein.
J Arnau, L Guerrero, C Sa rraga
390
TABLE 2
Values of the parameters showing signiÐcant interactionsa
HpH
NaCl low level
Cathepsin Bb
Cathepsins B ] Lb
Brightness
Pastiness
L pH
NaCl high level
NaCl low level
Mean
SE
Mean
SE
Mean
SE
0É5b
1É8b
5É2a
3É3a
0É53
1É24
0É3
0É4
5É4a
11É7a
3É1b
1É6b
1É76
2É08
0É8
0É4
2É5b
4É7b
2É0
0É6
1É59
1É59
0É5
0É2
NaCl high level
Mean
19É4a
39É3a
1É3
0É2
SE
3É39
9É18
0É2
0É1
a Means within HpH or LpH data with di†erent following letters are signiÐcantly di†erent (P \ 0É05).
b Cathepsin activities are given as units per mg of extracted protein.
the lack of signiÐcant di†erences found in NPN and Tyr
between the batches manufactured with di†erent
amounts of salt.
According to Parren8 o et al (1994) and Sarraga et al
(1993) cathepsins were more active during the initial
period of the manufacturing process. Cathepsin B is the
most stable of the enzymes studied (Parren8 o et al 1994)
and cathepsin D activity decreased more quickly, registering from 10 to 20% of its initial activity at the end of
the process (Sarraga et al 1993). According to our
results, NaCl concentration and pH a†ected cathepsin
B and B ] L activity to a greater extent than cathepsin
D activity at the end of the process.
The degree of proteolysis has been related to pastiness (Arnau 1991 ; Careri et al 1993) and brightness
(Guerrero et al 1996). However, in this study the HpH
hams registered more brightness, crumbliness, pastiness,
adhesivity and less hardness than the LpH hams (Table
3) in spite of having a lower NPN content. These attributes could be explained by the higher level of moisture
of Biceps femoris muscles in HpH (Table 1) and the
higher degree of extractibility (O†er and Trinick 1983 ;
Knight and Parson 1988) and functionality (higher
water-holding capacity, solubility, viscosity, . . .) of meat
proteins at high pH (Klement et al 1973, 1974 ; Shen
1981 ; Hamm 1986). The pH ] NaCl interaction (Table
2) showed that NaCl produced a more important
decrease in brightness and pastiness at HpH than at
LpH.
The di†erences found in pastiness and adhesivity
between batches 1 and 2 could be caused by the lower
degree of functionality of meat proteins at high NaCl
concentrations (Hamm 1986) since the di†erences found
in the proteolysis estimated as NPN are not signiÐcant
(Table 1). It is worth mentioning that the data were
determined at the end of the process and the study of
the proteolysis only at this point of the process was not
enough to fully explain the sensory characteristics
studied. LpH hams possessed the necessary characteristics for the product to be commercialised, whereas
HpH hams needed a longer drying period in order to
decrease their high moisture content (Table 1) and
increase the hardness of the product.
The surface of the HpH hams was rougher (more
rugose) than LpH hams because the lean tissue is more
easily deformed (Guerrero et al unpublished results) and
the phosphate crystals on the surface formed a drying
rim which made uniform retraction more difficult
(Arnau et al 1997b). A similar phenomenon can be
observed in Spanish non-acid dry sausages.
TABLE 3
pH and NaCl added e†ects on sensory characteristics of BF musclea
pH
24
High
Brightness
Hardness
Crumbliness
Pastiness
Adhesivity
Saltiness
pH ] NaCl
Added NaCl
L ow
High level (80b)
L ow level (55b)
Mean
SE
Mean
SE
Mean
SE
Mean
SE
4É12a
2É52b
4É84a
2É47a
4É36a
4É32b
0É50
0É27
0É21
0É36
0É47
0É31
1É63b
4É79a
3É03b
0É38b
1É17b
5É34a
0É28
0É22
0É32
0É12
0É19
0É25
2É54
3É78
4É31
0É90b
2É17b
5É64a
0É47
0É41
0É31
0É30
0É49
0É15
3É22
3É53
3É56
1É96a
3É36a
4É02b
0É61
0É43
0É42
0É45
0É63
0É26
a Means within pH or added NaCl with di†erent following letters are signiÐcantly di†erent (P \ 0É05).
24
b g kg~1 of ham.
*
NS
NS
*
NS
NS
pH and NaCl concentration in dry-cured hams
The saltiness level was obviously higher in the high
salt level batch than in the low salt level batch. The
more intense salty taste in the LpH hams could be produced by the slightly higher NaCl concentration, the
pH itself (Migaud and Frentz 1978), the higher concentration of products derived from proteolysis (Careri et
al 1993) and the lower Na migration to the outer layer
of the ham as Na HPO than that found in the HpH
2
4
hams. However, the higher water-holding capacity of
the HpH hams could lead to a higher amount of water
in certain parts of the ham which, in turn, could facilitate dissolution of the salt coming from the dryer outer
parts following the natural tendency to equilibrate the
NaCl/water ratio (Arnau et al 1995). A similar phenomenon was found by Stiebing and RoŽdel (1990) when
they studied the inÑuence of the pH on the drying
pattern in dry sausage. This migration is a†ected mainly
by the drying dynamics and could increase the total
amount of salt and the saltiness in the more humid
zones. This would explain the results of Poma (1980,
1991) who observed a higher NaCl concentration in
HpH hams. Consequently, the salty taste depends on
the dynamics of salt and water which are inÑuenced by
factors related to raw material characteristics and dehydration conditions during the process.
ACKNOWLEDGEMENT
This work was supported by INIA (Instituto Nacional
de Investigaciones Agrarias) project No Sc93-126. The
authors wish to thank Sr Kim Arbones for his technical
assistance.
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