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J Sci Food Agric 1998, 78, 559È564
Eþect of Irradiation Dose and Irradiation
Temperature on the Thiamin Content of Raw
and Cooked Chicken Breast Meat
William D Graham,1* the late M Hilary Stevenson1,2 and Eileen M Stewart1,2
1 Food Science Division, The Department of Agriculture for Northern Ireland,
Newforge Lane, Belfast, BT9 5PX, UK
2 The Department of Food Science, The QueenÏs University of Belfast, Newforge Lane,
Belfast BT9 5PX, UK
(Received 2 September 1997 ; revised version received 2 March 1998 ; accepted 6 April 1998)
Abstract : The usefulness of ionising radiation for the elimination of pathogenic
bacteria in poultry meat has been well documented as have the e†ects of this
processing treatment on the nutritional status of the food, in particular, the vitamins. Unfortunately, much of the earlier research carried out on the e†ect of
irradiation on vitamins was carried out in solution or in model systems at doses
much greater than those used commercially thereby resulting in considerable
destruction of these compounds. Thus, those opposed to the process of food
irradiation labelled the treated food as nutritionally poor. However, in reality,
due to the complexity of food systems the e†ects of irradiation on vitamins are
generally not as marked and many processes, for example cooking, cause the
same degree of change to the vitamins. Thiamin (vitamin B ) is the most radiation sensitive of the water-soluble vitamins and is therefore 1a good indicator of
the e†ect of irradiation treatment. In this study the e†ects of irradiation at either
4¡C or [20¡C followed by cooking on the thiamin content of chicken breast
meat was determined. Results showed that whilst both irradiation and cooking
resulted in a decrease in thiamin concentration, the losses incurred were unlikely
to be of nutritional signiÐcance and could be further minimised by irradiating the
chicken meat at a low temperature. Thiamin analyses were carried out using
high-performance liquid chromatography since this technique is faster and more
selective than the chemical or microbiological methods more commonly
employed. Total thiamin, both free and combined form, was determined following acid and enzyme hydrolysis. ( 1998 Society of Chemical Industry.
J Sci Food Agric 78, 559È564 (1998)
Key words : irradiation ; chicken breast meat ; thiamin ; vitamin B ; dose ;
cooking ; temperature ; high-performance liquid chromatography
Campylobacter. Other food poisoning organisms which
may be present include L isteria, Clostridia and Staphylococcus. Most foodborne disease attributed to the consumption of poultry and other meats is a consequence
of inadequate cooking of the product and/or improper
handling of the products after cooking (Klinger and
Lapidot 1993). However, extensive research has demonstrated that exposure of fresh poultry carcasses to an
irradiation dose of 2É5 kGy will signiÐcantly reduce the
number of bacterial pathogens, if present (Mulder 1982 ;
Kampelmacher 1983 ; Urbain 1983 ; Thayer et al 1991).
One of the main uses of low-dose irradiation is to
enhance food safety through the inactivation of pathogenic microorganisms such as Salmonella and Campylobacter which are known to be the most common agents
of food poisoning. It has been reported (Roberts 1990)
that 60È80% of poultry sold in the UK may be contaminated with Salmonella and up to 100% may contain
* To whom correspondence should be addressed.
( 1998 Society of Chemical Industry. J Sci Food Agric 0022È5142/98/$17.50.
Printed in Great Britain
These Ðndings have played a part in bodies such as the
Food and Drug Administration (FDA) in the USA
giving approval for the irradiation of chicken (FDA
1990), and the British Medical Association (BMA 1989)
identifying irradiation as the only processing technique
which is likely to overcome the problem of food poisoning from chicken. Doses higher than 2É5 kGy are,
however, required if the product is in the frozen state
and it has been demonstrated that irradiation can be
carried out with doses up to 7É5 kGy at low temperatures ([18¡C). Irradiation in the frozen state markedly reduces the organoleptic changes that would occur
at the same dose if treatment was carried out at 4¡C
(Coleby et al 1961 ; Mulder 1984).
In 1981 the report of the Food and Agriculture
Organisation/International Atomic Energy Agency/
World Health Organisation Joint Expert Committee on
Irradiated Food (JECFI 1981) concluded that “irradiation of food up to an overall average dose of 10 kGy
presents no toxicological hazard and introduces no
special nutritional or microbiological problemsÏ.
However, those opposed to the use of the irradiation
process have highlighted the loss of nutritional value of
foods as a major concern, especially with respect to
vitamins. Reports of high vitamin losses from irradiation are largely due to the fact that many early studies
were carried out using pure vitamin solutions, or by
using doses higher than those which would be used to
irradiate food commercially. Thus, actual losses were
overestimated and bore no relevance to what happens
in the actual food where the complexity of the composition of the food often protects individual vitamins from
destruction by ionising radiation (Kilcast 1994). In addition, other food preservation techniques, such as those
involving cooking, also destroy vitamins, so the e†ect of
irradiation on these minor components is not unique
(Stevenson 1994).
Thiamin (vitamin B ) is recognised as the most radi1
ation sensitive of the water-soluble vitamins as well as
being extremely heat labile (Josephson et al 1978). For
these reasons, thiamin is considered to be a good indicator of general vitamin losses in food. However, the
e†ect of irradiation on this vitamin may vary according
to the type of food and the conditions during the irradiation process (Diehl 1990).
As chicken meat is a signiÐcant source of thiamin in
the diet it is important that the e†ect of irradiation on
the concentration of this vitamin is studied along with
the inÑuence of cooking post-irradiation. However, considerable variations in the thiamin concentration of
irradiated chicken meat have been reported in the literature (Fox et al 1989 ; Hanis et al 1989). Therefore, this
study was designed to investigate the e†ects of irradiation dose and temperature of irradiation on the thiamin
content of raw and cooked chicken breast meat. In most
of the work reported to date, thiamin concentrations
have been determined by either chemical or microbio-
W D Graham, the late M H Stevenson, E M Stewart
logical methods. These methods are considered to be
time consuming and may be subject to interference from
other food components (Finglas and Faulks 1984).
High-performance liquid chromatography (HPLC)
coupled with Ñuorescence detection has the advantages
of selectivity and speed of analysis, therefore, it was
used as the means of thiamin analysis for this experimental work.
Sample preparation and analysis
Forty eight oven-ready chickens were obtained from a
local chicken processing plant in Northern Ireland in
order that all the samples used were from the same
batch and were fresh on the day of purchase. The
samples were maintained at chill temperature (4¡C)
prior to use. They were then divided into two groups of
24, the breasts removed and packed together in matching pairs. Twenty four matching pairs were irradiated at
an environmental temperature of 4 ^ 1¡C while the
other group of 24 was frozen at [20¡C prior to being
irradiated in dry ice at an environmental temperature of
1 ^ 1¡C. Four matching pairs were irradiated at doses
of either 1, 2É5, 5, 7É5 and 10 kGy whilst 4 were left
unirradiated and served as controls.
Cobalt 60 was used as the source of ionising radiation (Gammabeam 650, Nordion International Inc,
Kanata, Canada) at a dose rate of 1 kGy h~1. Two
perspex dosimeters (Type 3042 B, Harwell Dosimeters
Ltd, Harwell, UK) were placed one on either side of two
chicken breasts at each dose. The change in absorbance
of the dosimeters was measured spectrophotometrically
at 603 nm and the corresponding doses calculated using
calibration graphs provided by the National Physical
Laboratory (Teddington, Middlesex, UK).
Following irradiation, one breast from each matching
pair was wrapped in aluminium foil and cooked in a
convection oven at a temperature of 180¡C until the
internal temperature reached 82È87¡C. Frozen breasts
were allowed to thaw in a refrigerator at approximately
4¡C prior to cooking. Thiamin was determined by
HPLC using a modiÐcation of the method of Finglas
and Faulks (1984). Following removal of the skin and
bone, the chicken meat was cut and minced in order to
obtain a homogeneous sample. A 10 g sample was
blended with 50 ml of 0É1 M hydrochloric acid and
autoclaved for 30 min at 121¡C (103 kPa pressure).
After cooling to \50¡C, 5 ml of 2 M sodium acetate
bu†er and 5 ml of freshly prepared 5% (w/v) takadiastase were added to bring the pH to approximately 4É5.
The mixture was incubated for 2É5 h in a shaking
water bath maintained at 48¡C, cooled, diluted to
100 ml and Ðltered through Whatman No 541 Ðlter
paper. The Ðltrate obtained was used for thiamin
E†ect of irradiation dose, irradiation temperature and cooking on thiamin in chicken breast meat
analysis by conversion of thiamin to its thiachrome
derivative and subsequent injection of a 10 ll aliquot
into a HPLC (Hewlett Packard HP1090 Liquid
Chromatograph). The mobile phase used consisted of
60% methanol and 40% water. The Ñow rate was
0É9 ml min~1 and the HPLC column was a
25 cm ] 4É6 mm id ODS 2 column packed with 10 lm
spherisorb (Phase Separations Ltd, UK).
Conversion of thiamin to thiachrome was achieved
by addition of 3 ml freshly prepared alkaline ferricyanide solution (15 g sodium hydroxide and 1 g potassium ferricyanide per 100 ml) to 5 ml of the extract
which was left in the dark for 10 min. It is essential that
the latter procedure is carried out in subdued light.
Timing is also critical and injection of the sample into
the HPLC must be made within 5 min of completion of
the reaction. A Ñuorescence detector set at 375 nm excitation and 435 nm emission was used and identiÐcation
made by comparison with a standard thiamin solution
similarly derivatised. Standard solutions of thiamin prepared as described for the experimental samples, were
used to check recoveries of thiamin. The dry matter
content of the samples was determined after oven
drying (100¡C) duplicate 10 g samples to a constant
Statistical analysis
The experimental results were subjected to analysis of
variance using a Genstat 5 package.
Statistical analysis of the vitamin results expressed on
either a fresh matter or dry matter basis gave similar
results ; therefore, only the concentrations based on
fresh weight are referred to in this section although both
are presented in Table 1.
Overall, both irradiation dose and temperature had a
signiÐcant e†ect (P \ 0É001) on the thiamin content of
the chicken breast meat (Table 1 ; Fig 1). At an irradiation temperature of 4¡C (chilled state), the samples
given a dose of 1 kGy had similar thiamin concentrations to the non-irradiated control samples. However,
when the irradiation dose was increased to 2É5 kGy,
which is the dose used commercially for fresh poultry,
the thiamin content had decreased by approximately
20%. On the other hand, when the chicken was irradiated in the frozen state at [20¡C an approximate
reduction of only 6% was observed at the same dose.
The frozen samples were found to have approximately
16% more thiamin than those samples maintained at
4¡C. There was a linear decrease (P \ 0É001) in thiamin
content with increasing dose up to 10É0 kGy although
the diminution was less in the samples irradiated in the
frozen state compared with those treated at 4¡C. At a
Fig 1. E†ect of irradiation temperature and dose on the
thiamin concentration of uncooked and cooked chicken
breast meat (Standard error of the mean \ 7É89 ; n \ 8).
dose of 5É0 kGy the loss of thiamin in samples maintained in the chilled state during irradiation was
approximately 30% compared to 11% at [20¡C. When
samples were given 7É5 kGy, thiamin losses were 37%
and 21% for 4¡C and [20¡C, respectively, whilst at
10É0 kGy they were 43% and 21%, respectively. Whilst
a loss of approximately 20% thiamin occurred when the
samples maintained at 4¡C during irradiation were
given a dose of 2É5 kGy, a comparable loss only
occurred in the samples irradiated frozen at doses of 7É5
and 10É0 kGy.
As expected, cooking the chicken breasts resulted in a
signiÐcant reduction (P \ 0É01) in the thiamin content
of both irradiated and non-irradiated samples (Table 1 ;
Fig 1). Cooking reduced the thiamin content of the nonirradiated controls by approximately 20%, for both the
chilled and frozen samples. Thus, the thiamin loss sustained is equivalent to that caused by irradiation at a
dose of 2É5 kGy and a temperature of 4¡C. For samples
irradiated at [20¡C a combination of 2É5 kGy followed
by cooking is required to give a comparable depletion.
When samples irradiated in the fresh state at 4¡C
were cooked, the decrease in thiamin content varied
between 20 and 26% over the dose range of 1È10 kGy.
The e†ect of cooking was less marked in samples irradiated at [20¡C where thiamin losses ranging from 12 to
18% were recorded. At the commercial dose of 2É5 kGy,
the samples irradiated in the frozen state and cooked
retained 22% more thiamin than those samples which
were irradiated chilled and then cooked while the
uncooked frozen samples contained approximately 12%
more than those uncooked samples irradiated at 4¡C.
A highly signiÐcant two-way interaction was
observed between irradiation dose and cooking
(P \ 0É01). This was due to the occurrence of di†erent
linear trends with dose for the uncooked and cooked
samples. A constant diminution in thiamin concentration with dose, approximately 12% between each dose
level from 1 to 10 kGy, was observed for the cooked
samples. However, in the case of the uncooked samples
the reduction with dose was less pronounced as, for
W D Graham, the late M H Stevenson, E M Stewart
E†ect of irradiation dose, temperature of irradiation and cooking on the dry matter and thiamin content of chicken breast meat
Irradiation dose
Dry matter concentration (g kg~1)
T hiamin concentration (lg per 100 g FW )
T hiamin concentration (lg per 100 g DW )
SEM/SigniÐcance of e†ect
Dose (D)
Uncooked/cooked (C)
Chill/Frozen (F)
(n \ 32)
(n \ 96)
(n \ 96)
(n \ 16)
(n \ 16)
(n \ 48)
(n \ 8)
2É35 NS
2É90 NS
3É32 NS
1É68 NS
4É10 NS
7É89 NS
11É69 NS
28É64 NS
NS, not signiÐcant ; * P \ 0É05 ; ** P \ 0É01 ; *** P \ 0É001.
DW, dry weight ; FW, fresh weight ; TC, thiamin concentration.
example, there was a 12% decrease between the 1 and
2É5 kGy dose levels while the e†ect was less marked
between 7É5 and 10 kGy with a decrease of only 4%
being found.
The signiÐcant interaction (P \ 0É05) observed
between cooking and irradiation temperature was most
likely due to the fact that samples maintained at [20¡C
during irradiation and then cooked exhibited less of a
decrease in thiamin concentration than those irradiated
at 4¡C prior to cooking.
Irradiation had the e†ect of depleting thiamin content
at both irradiation temperatures employed and, as
stated earlier, the diminution increased with dose.
However, di†erent linear trends were found with dose
for each irradiation temperature which led to a highly
signiÐcant (P \ 0É01) interaction between irradiation
dose and temperature. The depletion of thiamin content
in samples irradiated at [20¡C was much less marked
than those treated at 4¡C. Similar concentrations of the
vitamin were measured in the frozen samples at both
the 7É5 and 10É0 kGy dose levels while the equivalent
amount in the chicken meat irradiated at chill temperature was found in samples which had received a
dose of 2É5 kGy.
The Ðndings of this work agreed with those reported
previously for bacon (Thayer et al 1989) beef liver
(Williams et al 1958) chicken (Fox et al 1989 ; Hanis et
al 1989), minced beef (Wilson 1959), pork (Fox et al
E†ect of irradiation dose, irradiation temperature and cooking on thiamin in chicken breast meat
1989) and turkey (Thomas and Calloway 1957 ; Fox et
al 1995). An increasing loss of thiamin in chicken meat
was observed with increasing irradiation dose but when
the irradiation treatment was carried out at freezing
temperatures there was a marked reduction in the
e†ects observed. Thus, the results conÐrm that destruction of the vitamin reÑects the dose applied and the
conditions used during irradiation.
However, as noted in the introduction, considerable
variations in thiamin concentration in chicken meat following irradiation have been reported in the literature.
Hanis et al (1989) recorded a loss of 43É6% thiamin
when chicken meat was given an irradiation dose of
5 kGy at an environmental temperature of 10¡C. This
depletion increased to 57É3% when a 10 kGy dose was
used. In comparison, the thiamin destruction due to
irradiation reported by Fox et al (1989) was much less
marked with a 27É2% loss being observed at a dose of
5 kGy and irradiation temperature of 10¡C. The results
reported in the present study clearly agree with those of
Fox et al (1989) as 30É2% less thiamin was measured in
samples given a dose of 5 kGy at a temperature of
10¡C. When chicken was irradiated at the same temperature with a 10 kGy dose the thiamin loss was
approximately 43É2%, being equivalent to that observed
by Hanis et al (1989) for a 5 kGy dose at 10¡C.
Both Fox et al (1989) and Hanis et al (1989) found
that less thiamin was destroyed when samples were irradiated in the frozen state which is in agreement with the
Ðndings of this experimental work. Fox et al (1989)
observed a loss of 8É8% at a dose of 3É3 kGy and irradiation temperature of [20¡C while Hanis et al (1989)
found a 22É4% loss when samples received 2É5 kGy at
[15¡C. The results reported by Fox et al (1989)
compare favourably with those recorded in the present
work where a diminution of 6% was measured when
chicken meat was irradiated in the frozen state with a
dose of 2É5 kGy.
Fox et al (1989) observed further thiamin losses when
irradiated chicken was cooked which was also the case
in this experimental work. According to Fox et al
(1995), the cookingÈdose e†ect appears to involve
chemical or physical changes in the tissues or vitamin
which result in increased vitamin destruction or
decreased extractability. However, substantially greater
thiamin losses due to cooking were observed in the
present study. Fox et al (1989) found that when chicken
meat was given an irradiation dose of 3É3 kGy at 0¡C
and cooked the thiamin concentration was approximately 10% less than that of cooked non-irradiated
samples. However, in this experimental work when
chicken was given an irradiation dose of 2É5 kGy at 4¡C
and cooked a thiamin loss of approximately 22% was
measured, being double that recorded by Fox et al
(1989). The variations observed could possibly be due to
the di†erences in cooking which although small, nevertheless illustrate the e†ect of heat on thiamin. Fox et al
(1989) cooked chicken breasts in a convection oven at
191¡C until the samples reached an internal temperature of 82¡C. In this experimental work the samples
were cooked to an internal temperature of 82È87¡C.
The Ðndings of this study support those of De Groot et
al (1972). These workers found that chicken irradiated
with a dose of 6 kGy contained approximately 27% less
thiamin than non-irradiated cooked chicken which is
comparable with the 26% reduction observed in this
work at the 5 kGy dose level. It should also be noted
that despite the fact there are reductions in the thiamin
content of meats following irradiation, the vitamin is
even more sensitive to heat than to irradiation.
Whilst cooking generally tends to increase vitamin
loss, in some instances, the combination of irradiation
and cooking has been shown to actually reduce losses.
When studying the e†ects of irradiation on the B vitamins in the legume red gram, Sreenivasan (1974) found
that the vitamins, thiamin included, were retained better
in samples irradiated and then cooked than in the corresponding non-irradiated controls. Irradiation resulted
in a reduced cooking time for the red gram and as prolonged heating is known to destroy the B vitamins it
was presumed that this reduction accounted for the
better retention of the vitamins in the radiationÈ
processed cooked samples. However, the Ðndings of
Sreenivasan (1974) were not observed in this study as
irradiation followed by cooking did not reduce thiamin
loss. Nevertheless, as indicated by Diehl (1990), further
studies of the combination e†ects of irradiation and
heat would be advantageous.
Whilst Hanis et al (1989) reported a threshold dose
level of 0É5 kGy for chicken meat, the present study
found a threshold e†ect up to 1É0 kGy. Fox et al (1989)
did not observe any threshold e†ect for either chicken
meat or pork. The greater thiamin losses reported by
Hanis et al (1989) are difficult to explain although, since
a spectrophotometric method was used, they may be
due to interference from other food components
present. The advantage of the HPLC methodology used
in the present study, apart from speed, is its selectivity.
As reported in the experimental section of this paper
both the preparation of the thiachrome derivative and
its subsequent injection into the HPLC system are critical due to the instability of the thiachrome and may be
the root cause of any discrepancies.
Thiamin concentrations were reduced by irradiation but
when the process was carried out at [20¡C the e†ect
was minimised thus emphasising the importance of
optimising irradiation conditions. The loss of thiamin
following cooking was similar in both non-irradiated
and irradiated samples, thereby illustrating the fact that
other food processes can cause the same degree of
W D Graham, the late M H Stevenson, E M Stewart
change to the nutrients. Although there was a decrease
in the thiamin concentration of chicken meat following
irradiation, it should be borne in mind that chicken is
only one of a number of sources of thiamin in the
human diet. Therefore, the reduction in total thiamin
intake of an individual consuming irradiated chicken
will be considerably less than 20%.
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