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Author's personal copy
Meat Science 80 (2008) 903–909
Contents lists available at ScienceDirect
Meat Science
journal homepage: www.elsevier.com/locate/meatsci
Effect of electron-beam irradiation before and after cooking on the chemical
properties of beef, pork, and chicken
Joong-Ho Kwon a, Youngju Kwon a, Ki-Chang Nam b, Eun Joo Lee c, Dong U. Ahn c,*
a
Department of Food Science and Technology, Kyungpook National University, Daegu 702-701, Republic of Korea
Examination Division of Food and Biological Resources, Korean Intellectual Property Office, Daejeon 302-701, Republic of Korea
c
Department of Animal Science, Iowa State University, 1221 Kildee Hall, Ames, IA 50011-3150, USA
b
a r t i c l e
i n f o
Article history:
Received 20 February 2008
Received in revised form 8 April 2008
Accepted 9 April 2008
Keywords:
Irradiation
Cooking
TBARS
Volatiles
Carbon monoxide production
a b s t r a c t
Ground beef, pork, and chicken thigh meats were irradiated at 0 or 5.0 kGy before and after cooking and
then stored at 40 °C in oxygen permeable bags. The pH, lipid oxidation, volatiles, and carbon monoxide
production of the meat were determined at 0 and 6 months of storage. The pH values of raw meats from
different animal species were different (5.36–6.25) and were significantly increased by cooking, irradiation, and storage (p < 0.05). Irradiation had no effect on the TBARS values of ground beef and pork, but
significantly increased the TBARS of chicken thigh meat. Cooking, whether it was done before or after
irradiation, caused significant increase in TBARS and was most significant in chicken and pork. The numbers of volatiles analyzed by GC/MS were higher in irradiated meats than the non-irradiated ones regardless of meat source. Sulfur-containing compounds were newly produced or increased by irradiation, but
dimethyl disulfide and dimethyl trisulfide were not detected in the non-irradiated meats regardless of
cooking treatment. Irradiation time, whether done before or after cooking, had little effect on the TBARS,
volatiles, and carbon monoxide production in the meat.
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
It is known that the use of high-quality ingredients and
advanced processing technologies including irradiation has excellent potential, particularly in combination in achieving safety and
quality improvements in food processing (Davis, Sebranek, Lonergan, Ahn, & Lonergan, 2004). Irradiation has been studied extensively for improving the safety of meat products. Olson (1998)
indicated that low-dose (<10 kGy) irradiation can kill at least
99.9% of Salmonella in poultry and an even higher percentage of
E. coli O157:H7. The US Food and Drug Administration (FDA) approved irradiation for poultry and red meats to control foodborne
pathogens and extend the products’ shelf life (Gants, 1998). Irradiation was approved for poultry at 2.5 kGy and fresh and frozen red
meats up to 4.5 and 7.0 kGy, respectively (USDA, 1999).
However, the chemical changes of meat and poultry induced by
irradiation are of concern, making it difficult for the meat industry
to use the technology to achieve its food safety benefits. Irradiation
is reported to accelerate lipid oxidation (Ahn, Jo, & Olson, 2000;
Katusin-Razem, Mihaljevic, & Razem, 1992), produce a characteristic off-odour (Ahn, Nam, Du, & Jo, 2001; Patterson & Stevenson,
1995), and change the color (Lynch, MacFie, & Mead, 1991; Nam
& Ahn, 2002) of meat.
* Corresponding author.
E-mail address: duahn@iastate.edu (D.U. Ahn).
0309-1740/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.meatsci.2008.04.009
The chemical changes of irradiated meats are initiated by the
free radicals produced during irradiation, and the production of
sulfur volatiles or carbon monoxide is caused by reactions between
meat components and radiolytic free radicals (Ahn, 2002; Nam &
Ahn, 2002). The chemical reactions and lipid oxidation, volatiles
production, and gas production associated with the changes in
quality and sensory properties of raw meats have been well-demonstrated, but little is known on the corresponding chemical
changes as influenced by cooking and irradiation.
The objective of this work was to determine the effect of electron-beam irradiation applied before or after cooking on the chemical properties of ground beef, pork, and chicken meat during
storage and provide information on how to control the quality
defects in precooked irradiated or cooked irradiated meats.
2. Materials and methods
2.1. Cooking and irradiation of meat samples
Fresh meats (beef loins, pork loins, and chicken thighs) were
purchased from three different local grocery stores and the meat
from each store was used as a replication. Meats were ground
through a 5-mm plate and vacuum-packaged in oxygen impermeable bags (nylon/polyethylene, 9.3 mL O2/m2/24 h at 0 °C; Koch,
Kansas City, MO, USA). Five treatments were prepared for each
meat from different animal species: (1) non-irradiated raw meat,
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(2) irradiated raw meat, (3) non-irradiated cooked meat, (4) precooked irradiated meat (cooked, 5 kGy), (5) irradiated and then
cooked meat (5 kGy-cooked) samples. Cooking of irradiated or
non-irradiated meats was done in the package at 85 °C in a water
bath to an internal temperature of 75 °C. After cooking, meats were
repackaged in oxygen permeable bags (polyethylene, 4 6, 2 mil,
Associated Bag Co., Milwaukee, WI, USA), and then subjected to
either frozen storage or irradiation and then frozen storage. Irradiation was done with accelerated electrons using a Linear Accelerator (Circe IIIR, Thomson CSF Linac, St. Aubin, France) at 5 kGy. The
energy and power levels used were 10 MeV and 10.2 kw, respectively, and the average dose rate was 92.0 kGy/min. The max/min
ratio was approximately 1.18 for 5 kGy. The absorbed dose was assured by 2 alanine dosimeters placed on the top and bottom of one
meat sample per cart and was read using a 104 Electron Paramagnetic Resonance Instrument (Bruker Instruments Inc., Billerica, MS,
USA). Immediately after irradiation, a portion of irradiated raw
meat was cooked as described above. Samples were analyzed at
0 day and 6 months of storage at 40 °C.
2.2. pH and 2-thiobarbituric acid-reactive substances (TBARS)
Meat samples were homogenized in 10 volumes of deionized
distilled water (DDW) and centrifuged at 3000g for 15 min. The
pH of the supernatant was measured using a pH meter (ThermoOrion Model 420A, Beverly, MA, USA). Lipid oxidation was determined by a TBARS method (Ahn et al., 1998). Minced sample
(5 g) was placed in a 50-mL test tube and homogenized with
15 mL deionized distilled water (DDW) using a Brinkman Polytron
(Type PT 10/35; Brinkman Instrument, Inc., Westbury, NY) for 15 s
at high speed. The meat homogenate (1 mL) was transferred to a
disposable test tube (13 100 mm), and 50 lL butylated hydroxytoluene (7.2% in ethanol) and 2 mL of thiobarbituric acid/trichloroacetic acid (20 mM TBA and 15%, w/v, TCA) solutions were added.
The mixture was vortex-mixed and incubated in a 90 °C water bath
for 15 min. After cooling, the samples were vortex-mixed and centrifuged at 3000g for 15 min. The absorbance of the resulting upper
layer was read at 532 nm against a blank (1 mL DDW + 2 mL TBA/
TCA). The amounts of TBARS were expressed as mg of malondialdehyde (MDA) per kg of meat.
2.3. Volatile compounds
A dynamic headspace analysis was performed using a Solartek
72 Multimatrix-Vial Autosampler/Sample Concentrator 3100
(Tekmar-Dohrmann, Cincinnati, OH, USA) connected to a GC/MS
(HP 6890/HP 5973, Hewlett Packard Co., Wilmington, DE, USA)
according to the method of Ahn et al. (2001). Minced sample
(3 g) was placed in a 40-mL vial, flushed with helium (He, 40 psi)
for 3 s, and capped airtight with a Teflon-fluorocarbon resin/silicone septum (I-Chem Co.). The maximum waiting time in a loading
tray (4 °C) was less than 2 h to minimize oxidative changes before
analysis. The meat sample was purged with helium (40 mL/min)
for 14 min at 40 °C. Volatiles were trapped using a Tenax/charcoal/silica column (Tekmar-Dohrmann) and desorbed for 2 min at
225 °C, focused in a cryofocusing module ( 80 °C), and then thermally desorbed into a column for 60 s at 225 °C. An HP-624 column
(7.5 m, 0.25 mm i.d., 1.4 lm nominal), HP-1 column (52.5 m,
0.25 mm i.d., 0.25 lm nominal), and HP-Wax column (7.5 m,
0.250 mm i.d., 0.25 lm nominal) were connected. Ramped oven
temperature was used to improve volatile separation. The initial
oven temperature of 0 °C was held for 1.5 min. The oven temperature was then increased to 15 °C at 2.5 °C per min, to 45 °C at 5 °C
per min, to 110 °C at 20 °C per min, and to 170 °C at 10 °C per min
and held for 2.25 min at that temperature. Constant column pressure at 22.5 psi was maintained. The ionization potential of MS was
70 eV, and the scan range was 19.1–350 m/z. Identification of volatiles was achieved using the Wiley library (Hewlett Packard Co.).
The area of each peak was integrated using ChemStation software
(Hewlett Packard Co.) and the total peak area (total ion
counts 104) was reported as an indicator of volatiles generated
from the samples.
TM
2.4. Carbon monoxide production
Ground meat sample (10 g) was placed in a 24-mL screw-cap
glass vial with a Teflon-fluorocarbon resin/silicone septum
(I-Chem. Co., New Castle, DE, USA). The vial was heated using a
microwave oven for 10 s at full power (1200 W) to release gas
compounds from the sample. After 5 min cooling at ambient temperature, the headspace (200 lL) was withdrawn using an airtight
Table 1
Effect of irradiating meat before or after cooking on pH
Cooking time
Raw meat
Raw meat
Cooked before IR
Cooked before IR
Cooked after IR
a–d
x,y
IR dose (kGy)
0
5
0
5
5
Beef
Pork
Chicken
0 month
6 months
0 month
6 months
0 month
6 months
5.36 ± 0.01cy
5.49 ± 0.04by
5.77 ± 0.01ay
5.78 ± 0.03ax
5.82 ± 0.03ax
5.61 ± 0.04dx
5.69 ± 0.02cx
5.90 ± 0.03ax
5.82 ± 0.01bx
5.88 ± 0.03ax
5.89 ± 0.02cy
5.86 ± 0.01cy
6.12 ± 0.09by
6.28 ± 0.01ay
6.14 ± 0.02bx
5.95 ± 0.03dx
6.05 ± 0.03cx
6.35 ± 0.03ay
6.38 ± 0.03ax
6.21 ± 0.07bx
6.25 ± 0.01cy
6.33 ± 0.02by
6.49 ± 0.04ay
6.55 ± 0.03ay
6.51 ± 0.04ay
6.45 ± 0.06cx
6.53 ± 0.02bx
6.43 ± 0.05ay
6.66 ± 0.02ax
6.65 ± 0.03ax
Means with different letters within a column are significantly different (p < 0.05), n = 3.
Means with different letters for the same species within a row are significantly different (p < 0.05), n = 3.
Table 2
Effect of irradiating meat before or after cooking on TBARS during storage
Cooking time
Raw meat
Raw meat
Cooked before IR
Cooked before IR
Cooked after IR
a–e
x,y
IR dose (kGy)
0
5
0
5
5
Beef (mg MDA/kg meat)
Pork (mg MDA/kg meat)
Chicken (mg MDA/kg meat)
0 month
0 month
0 month
6 months
dx
1.02 ± 0.01
1.11 ± 0.05cx
1.56 ± 0.03ay
1.36 ± 0.04bx
1.36 ± 0.07bx
cx
1.00 ± 0.04
1.17 ± 0.10cx
1.83 ± 0.05ax
1.49 ± 0.27bx
1.48 ± 0.08bx
6 months
bx
0.41 ± 0.02
0.40 ± 0.05bx
0.97 ± 0.05ay
0.90 ± 0.06ay
0.91 ± 0.04ay
Means with different letters within a column are significantly different (p < 0.05), n = 3.
Means with different letters for the same species within a row are significantly different (p < 0.05), n = 3.
cx
0.48 ± 0.04
0.52 ± 0.06cx
1.75 ± 0.28ax
1.49 ± 0.05bx
1.40 ± 0.04bx
6 months
cx
0.53 ± 0.04
1.09 ± 0.07bx
1.16 ± 0.10bx
1.49 ± 0.18ax
1.20 ± 0.02bx
0.58 ± 0.12cx
0.95 ± 0.13bx
1.57 ± 0.10ay
1.68 ± 0.23ax
1.65 ± 0.16ay
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linear model of SAS software (SAS Institute Inc., 1995). Student–
Newman–Keul’s multiple range test was used to compare the
mean values of treatments. Mean values and standard error of
the means (SEM) were reported (p < 0.05).
syringe and injected into a GC (HP 6890, Hewlett Packard Co.). A
Carboxen-1006 Plot column (30 m 0.32 mm i.d., Supelco, Bellefonte, PA, USA) was used to analyze the carbon monoxide produced
by irradiation. The oven temperature was 120 °C and helium was
the carrier gas at a constant flow of 2.4 mL/min. Flame ionization
detector (FID) equipped with a Nickel catalyst (Hewlett Packard
Co.) was used as a detector, and the temperatures of inlet, detector
and Nickel catalyst (Hewlett Packard Co.) were set at 250, 280, and
375 °C, respectively. Detector air, hydrogen, and make-up gas (He)
flows were 400, 40, and 50 mL/min, respectively. The identification
of gas compounds was determined using standard gases (CO, Aldrich, Milwaukee, WI, USA and CO2, Praxair, Danbury, CT, USA)
and a GC/MS (Model 5873, Hewlett Packard Co.). The area of the
CO peak was integrated using the Chemstation software (Hewlett
Packard Co.). In order to quantify the amount of CO released, peak
area (pA s) was converted to a gas concentration (ppm or%) contained in the headspace (14 mL) of 10 g meat samples using the
concentration of CO2 in air (330 ppm).
3. Results and discussion
3.1. pH and Lipid oxidation (TBARS)
The pH of chicken thigh meat was the highest, followed by pork
and beef (Table 1). The pH of cooked meats were higher than that
of raw meat (p < 0.05) regardless of irradiation, and storage increased the pH (p < 0.05) of meat, especially in raw meats. Beef
showed the highest TBARS values, followed by chicken, and pork
(Table 2). Cooking before or after irradiation at 5 kGy caused a significant increase in TBARS, especially in chicken and pork. Among
the meat species, the highest TBARS value was observed in beef.
The susceptibility of meat to lipid peroxidation varies among
meats from different animal species and muscles from the same
animal (Rhee, Anderson, & Sams, 1996; Rhee & Ziprin, 1987; Salih,
Price, Smith, & Dawson, 1989). Kim, Nam, and Ahn (2002) reported
that raw beef is more susceptible to lipid oxidation than raw poultry and pork, but cooked poultry meat such as Turkey was more
2.5. Statistical analysis
The experiment was conducted in a completely randomized design with four replications. Data were analyzed using a generalized
Table 3
Effect of irradiating meat before or after cooking on CO production during storage at
Cooking time
IR dose (kGy)
0 month
Raw meat
Raw meat
Cooked before IR
Cooked before IR
Cooked after IR
0
5
0
5
5
40 °C
Beef (ppm)
Pork (ppm)
6 months
ex
1.7 ± 0.1
29.1 ± 0.6cy
17.1 ± 0.8dy
40.7 ± 1.0ay
35.6 ± 0.5by
ND
237.3 ± 18.0cx
59.0 ± 25.2dx
347.3 ± 91.4bx
499.7 ± 46.9ax
0 month
Chicken (ppm)
6 months
dx
2.7 ± 0.2
24.2 ± 1.6by
18.2 ± 0.2cy
30.3 ± 1.7ay
31.3 ± 0.2ay
0 month
ND
191.7 ± 23.0cx
27.0 ± 5.3dx
426.0 ± 51.9ax
321.3 ± 41.6bx
6 months
ex
1.7 ± 0.1
17.6 ± 0.5cy
11.0 ± 0. 9dy
29.5 ± 1.4ay
27.1 ± 0.6by
ND
360.7 ± 26.4ax
214.5 ± 1.5bx
404.0 ± 37.4ax
370.0 ± 97.6ax
ND – not detected.
a–e
Means with different letters within a column are significantly different (p < 0.05), n = 3.
x,y
Means with different letters for the same species within a row are significantly different (p < 0.05), n = 3.
Table 4
Effect of irradiating beef before or after cooking on volatile profiles at 0 month
Volatile compound
2-Propanone
Pentane
Dimethyl sulfide
Ethanol
2-Butanone
2,3-Butadione
3-Methyl butanal
2-Methyl butanal
1-Heptene
Heptane
Pentanal
3-Methyl heptane
Dimethyl disulfide
Toluene
1-Octene
Octane
2-Octene
5-Methyl-2-heptene
Hexanal
1-Nonane
Nonane
1-Pentanol
Heptane
Dimethyl trisulfide
Total
a–c
Raw meat (Total ion counts 104)
Cooked before IR (Total ion counts 104)
Cooked after IR (Total ion counts 104)
0 kGy
5 kGy
0 kGy
5 kGy
5 kGy
SEM
4099
2314
721
43,346
0b
0
0b
0b
0
0
0b
0
0b
0b
0b
893
247
634
528b
0
0b
3753a
0c
0b
5653
2541
1593
1064
44,002
3803a
485
110b
0b
0
641
0b
0
2833ab
168ab
197ab
1411
455
432
652b
0
261ab
2469ab
0c
0b
6312
5796
1242
790
36,881
0b
0
0b
0b
0
105
2074a
148
0b
0b
0b
1178
234
0
16352a
434
293ab
2417ab
814b
0b
6876
8620
1659
0
40,682
3344a
1749
913a
547a
485
979
1312a
0
2872ab
360a
463a
1539
104
233
6336b
115
460a
1623b
1413a
0b
7582
5182
928
662
47,288
3162a
1038
789a
204b
405
669
2328a
0
5933a
220ab
469a
1970
381
226
15129a
128
416a
1547b
367c
485a
8992
2269
632
537
7723
657
844
61
91
135
227
271
663
945
70
95
394
128
187
2370
124
77
432
111
149
1248
Means with different letters within a row are significantly different (p < 0.05), n = 3.
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susceptible to oxidative change than red meat (Akamittath, Brekke,
& Schamus, 1991; Salih et al., 1989). Ahn et al. (1998) addressed
the importance of the initial conditions of raw meat on the subsequent storage stability of cooked meat. Although free radicals are
known to accelerate lipid oxidation in meat (Jo & Ahn, 2000), the
effect of irradiation was not apparent in raw meat. Cooking significantly increased the TBARS in all meat samples, and storage for
6 months at 40 °C significantly increased the TBARS of cooked
meats.
3.2. Carbon monoxide production
Irradiation as well as cooking produced CO (Table 3). Carbon
monoxide was also detected in non-irradiated meat samples, but
the concentration was increased significantly by irradiation. Furuta, Dohmaru, Katayama, Toratoni, and Takeda (1992) reported that
radiolytic CO gas was detected in irradiated beef, pork, and poultry
meat. Carbon monoxide is a strong ligand to heme pigments, thus
it could affect the color of irradiated meat. Nam and Ahn (2002)
Table 5
Effect of irradiating pork before or after cooking on volatile profiles at 0 month
Volatile compound
2-Methyl butane
Pentane
Dimethyl sulfide
Ethanol
2-Propanol
2-Butanone
2,3-Butadione
3-Methyl butanal
2-Methyl butanal
1-Heptene
Heptane
Pentanal
Dimethyl disulfide
Toluene
1-Octene
Octane
2-Octene
Hexanal
1-Nonane
Nonane
1-Pentanol
Heptanal
Dimethyl trisulfide
Total
a–c
Raw meat (Total ion counts 104)
Cooked before IR (Total ion counts 104)
Cooked after IR (Total ion counts 104)
0 kGy
5 kGy
0 kGy
5 kGy
5 kGy
SEM
27,943
1073
907
0b
2402
0b
0
0b
0
0b
0b
0b
0b
260b
0b
87b
0
588b
0
0c
0b
0b
0b
33,263b
16,245
1283
2135
438,063a
1236
0b
0
0b
0
605ab
688ab
0b
3394ab
616ab
0b
663b
0
253b
0
312b
0b
0b
0b
465,499a
23,959
3681
573
72,135b
1063
0b
199
0b
0
0b
553ab
2743a
0b
500ab
0b
597b
0
3517a
0
0c
411a
668a
0b
145,970b
9059
1446
249
33,342b
239
923a
207
457a
0
737ab
1139a
1588ab
4317a
732a
483a
1692a
69
1197ab
275
593a
57b
565ab
489a
71,162b
2765
5187
815
367,827a
1328
0b
0
606a
140
1675a
1189a
3531a
3405ab
858a
622a
1527a
224
3630a
91
650a
315ab
415ab
535a
457,753a
11,785
904
493
60,054
502
33
128
49
62
297
192
536
828
104
80
207
59
746
74
68
85
132
59
73,940
Means with different letters within a row are significantly different (p < 0.05), n = 3.
Table 6
Effect of irradiating chicken before or after cooking on volatile profiles at 0 month
Volatile compound
2-Propanone
2-Methyl butane
Pentane
Dimethyl sulfide
Ethanol
2-Propanol
2-Butanone
2,3-Butadione
3-Methyl butanal
2-Methyl butanal
1-Heptene
Heptane
Pentanal
3-Methyl heptane
Dimethyl disulfide
Toluene
1-Octene
Octane
2-Octene
Hexanal
1-Nonane
Nonane
1-Pentanol
Heptanal
Dimethyl trisulfide
Total
a–c
Raw meat (Total ion counts 104)
Cooked before IR (Total ion counts 104)
Cooked after IR (Total ion counts 104)
0 kGy
5 kGy
0 kGy
5 kGy
5 kGy
SEM
596b
0
0b
0
15,886b
0
569
0
0c
0
0b
0c
0c
0
0c
0b
0b
583b
0
518c
0a
492b
0c
0b
0c
18,645c
3094b
0
0b
0
33,956a
274
634
525
0c
0
398b
681c
0c
0
0c
0b
201b
1138b
97
777c
0b
367b
591b
0c
0c
42,788bc
1280b
0
1571b
0
35,064a
0
386
0
0c
609
0b
296c
1852b
0
0c
0b
0b
1078b
0
1960b
0b
604ab
2165a
798b
0c
65,038b
12,323a
140
21,639a
3443
39,308a
1080
781
0
1092a
588
1859ab
2989a
3785a
0
12,027a
448a
728a
2430a
0
3208a
160b
900a
2491a
1488a
1545a
143,335a
5016b
337
18,482ab
1062
46,767a
1226
869
626
617b
139
2692a
1990b
2439b
296
7515b
309ab
837a
2616a
122
1902b
0b
0c
952b
661b
673b
115,278a
1535
163
4493
1563
4778
324
206
206
303
150
520
296
336
68
830
79
69
180
69
2877
339
91
173
69
52
53,580
Means with different letters within a row are significantly different (p < 0.05), n = 3.
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elucidated the mechanism of pink color generation in irradiated
pork or poultry, which involved the carbon monoxide produced
by irradiation. The amounts of CO in irradiated meats were also
significantly higher than non-irradiated ones even after 6 months
of storage.
3.3. Volatiles of irradiated meat
The effect of irradiation before or after cooking on the volatiles
of the three kinds of meat was monitored at 0 and 6 months of
storage at 40 °C. The number of volatiles detected at 0 month
was 24 in beef, 23 in pork, and 25 in chicken (Tables 4–6). More
than 1000 volatile compounds have been identified as flavor and
aroma compounds in commonly consumed beef, pork, poultry,
and lamb (Ramarathnam, Rubin, & Diosady, 1993).
Irradiated meats produced more volatiles than the non-irradiated ones regardless of meat species, but the degree of volatile
change varied significantly among the meats. Pork produced the
greatest amount of total volatiles, but the increase in volatiles after
irradiation was the highest in chicken. Irradiation produced new
Table 7
Effect of irradiating beef before or after cooking on volatile profiles after 6 months of storage at
Volatile compound
Acetaldehyde
Pentane
Propanal
2-Propanone
Methanol
Ethanol
1-Hexene
2-Propanol
Methane
Hexane
2-Butanone
2-Butanal
1-Heptene
Heptane
Pentanal
Dimethyl disulfide
Toluene
1-Octene
Octane
2-Octene
1-Butanol
Hexanal
10-Pentanol
Heptanal
Total
a–d
Raw meat (Total ion counts 104)
Cooked after IR (Total ion counts 104)
0 kGy
5 kGy
0 kGy
5 kGy
5 kGy
SEM
743c
1326
0c
12,150
466
5209
0c
0c
0c
0c
0c
0c
0c
151b
0b
0c
0c
0b
454
0
532a
711b
630
0c
23,713d
221c
1995
194c
10,932
160
3100
233b
3633b
0c
91c
3633b
91c
274a
726b
371b
2054b
118b
132ab
635
63
131b
2738b
665
209
29,886d
991c
2090
776b
9754
597
2405
0c
0c
0c
0c
0c
0c
0b
440b
1714a
0c
0c
0b
702
47
428a
11,430a
854
120bc
42,783c
19,708a
2185
1985a
12,242
791
6370
366a
5099a
1587a
2266a
5099a
2266a
370a
1174a
2085a
2255b
247a
233a
1090
97
543a
10,596a
893
491a
82,209b
15,804b
2191
1519a
9980
976
6676
0c
3578b
689b
1311b
3578b
1311b
438a
527b
2190a
3835a
160b
204a
1065
60
528a
12,416a
767
191b
102,163a
500
318
160
848
196
845
26
161
84
66
161
66
42
97
211
424
27
35
153
38
62
1494
176
41
3067
Means with different letters within a row are significantly different (p < 0.05), n = 3.
Table 8
Effect of irradiating pork before or after cooking on volatile profiles after 6 months of storage at
Volatile compound
Acetaldehyde
Butane
1-Pentene
Pentane
Propanal
2-Propanone
Methane
Methanol
Ethanol
2-Propanol
Tetrahydrofuran
3-Methyl butanal
1-Heptene
Heptane
Pentanal
Dimethyl disulfide
Toluene
1-Octene
Octane
1-Butanol
Hexanal
1-Nonane
Nonane
1-Pentanol
Heptanal
Total
a–c
40 °C
Cooked before IR (Total ion counts 104)
Raw meat (Total ion counts 104)
40 °C
Cooked before IR (Total ion counts 104)
Cooked after IR (Total ion counts 104)
0 kGy
5 kGy
0 kGy
5 kGy
5 kGy
SEM
143b
101
0
0
0c
0b
0
0
23,946b
43
0b
817b
0b
0b
20b
0
33c
0b
0b
0
536b
0b
0
0b
0c
25,641b
394b
5107
52
417
0c
289b
686
184
20,263b
561
107ab
774b
187b
227ab
254b
136
125bc
56b
195b
74
1562b
0
15
20b
87c
31,779b
45b
6770
0
1520
26c
1043b
1930
315
11,363b
215
124ab
35c
6b
346ab
736b
0
181bc
0b
180b
59
7595b
0b
56
313b
97c
32,961b
19,190a
4432
525
3356
1809a
3985a
2758
255
11,338b
907
358a
1696a
1031a
1214a
3271a
44
669a
280a
853a
158
25,136a
106a
65
855a
354a
84,652b
6634b
15,155
245
2731
1065b
2308ab
31,453
444
56,226a
1168
159ab
835b
464b
1047a
3209a
690
414ab
117b
799a
218
25,202a
51ab
77
980a
243b
151,940a
1750
5734
220
1043
151
580
7070
223
6126
518
75
160
153
232
322
247
85
40
133
50
2793
17
52
25
29
14,854
Means with different letters within a row are significantly different (p < 0.05), n = 3.
Author's personal copy
908
J.-H. Kwon et al. / Meat Science 80 (2008) 903–909
Table 9
Effect of irradiating chicken before or after cooking on volatile profiles after 6 months of storage at
Volatile compound
Acetaldehyde
1-Pentene
Pentane
Propanal
2-Propanone
Methanol
Ethanol
1-Hexene
2-Propanol
Hexane
2-Hexene
2-Butanone
Butanal
Methane
Benzene
1-Heptene
Heptane
Pentanal
2-Heptene
Dimethyl disulfide
Toluene
1-Octene
Octane
1-Butanol
Hexanal
1-Pentanol
Heptanal
Total
a–d
Raw meat (Total ion counts 104)
40 °C
Cooked before IR (Total ion counts 104)
Cooked after IR (Total ion counts 104)
0 kGy
5 kGy
0 kGy
5 kGy
5 kGy
SEM
107c
0b
228c
0b
22,989a
0
1306b
0b
1240
257c
0b
184c
121b
170b
0b
0c
31c
0c
0b
0c
0b
0b
66b
0b
198b
0
0d
26,901d
865c
300ab
9407b
57b
9675b
298
13,862a
625a
2347
985bc
16b
929a
99b
0b
16b
807b
885bc
620bc
0b
723c
169a
242b
598b
93ab
3185b
240
202c
48,463cd
3178b
0b
16,989ab
436b
9178b
303
4367b
0b
1249
2022ab
0b
546b
281b
2228b
84b
136c
1171bc
1350b
0b
0c
0b
16b
1462b
131ab
1465ab
876
262bc
63,940c
14,685a
484a
23,379a
1417a
11,959b
175
4387b
779a
1453
2652a
97a
897a
1534a
5991b
1089a
1871a
3886a
3505a
65a
5579a
0b
677a
2702a
195a
21,817a
625
541a
112,434b
13,875a
528
15,996ab
1140a
9896b
566
7304b
774a
1885
1668ab
70a
1049a
1177a
68,572a
303b
2065a
1784b
2805a
52ab
3428b
0b
268b
942b
104ab
14,108ab
392
375b
151,134a
595
113
2534
135
903
125
1767
45
370
335
15
53
159
3138
212
93
353
325
13
534
10
93
371
40
4071
192
40
8083
Means with different letters within a row are significantly different (p < 0.05), n = 3.
volatiles (1-butene, 1-pentene, 1-hexene, 1-heptene, dimethyl
disulfide, and dimethyl trisulfide) in all three meats that were
not found in non-irradiated meat as reported by Ahn et al.
(2000). In addition to these new volatiles, irradiation increased
the amounts of butane, dimethyl sulfide, hexane, and heptane already found in non-irradiated meats. These new and increased volatiles produced by irradiation supported the idea that irradiation
odour in meats was caused mainly by sulfur compounds, the radiolytic products of amino acids such as methionine and cysteine, and
the interactions of the sulfur compounds with hydrocarbons (Ahn,
2002; Ahn & Lee, 2002; Jo & Ahn, 2000).
Cooking influenced the formation of some volatile compounds
and increased the amounts of volatiles with the action of irradiation. Cooking significantly increased the amount of aldehydes,
but the effect of cooking on the production of sulfur volatiles like
dimethyl disulfide and dimethyl trisulfide was minimal. In addition, the differences in sulfur volatiles between precooked irradiated and irradiated cooked meats were minimal and inconsistent.
Thus, it was concluded that sulfur volatiles were mainly generated
by irradiation, and the sulfur volatiles were responsible for the
characteristic irradiation off-odour.
Initially, major volatiles found in irradiated meats were 2-butanone, heptane, dimethyl disulfide, toluene, and 1-octene for beef;
1-heptene, heptane, and dimethyl disulfide for pork; and 2-propanol, 1-heptene, dimethyl disulfide, and 1-octene for chicken. After
6 months of storage, however, the major volatiles changed significantly (Tables 7–9). Among the animals, the irradiated pork and
chicken produced more sulfur-containing volatiles than irradiated
beef. The amounts and number of volatiles in irradiated meats
were similar to that of the non-irradiated ones. Frozen storage
for 6 months in oxygen permeable packaging resulted in a decrease
in sulfur volatiles but an increase in aldehydes such as hexanal,
pentanal, propanal, and heptanal, indicating increased lipid oxidation, especially in cooked meat. The majority of sulfur-containing
compounds disappeared after 6 months of storage. Consequently,
if raw or cooked meats are irradiated and stored under aerobic conditions, formation of oxidative rancid flavor rather than irradiation
odour could be a problem.
4. Conclusion
Irradiation increased lipid oxidation in meat, but cooking was
more critical in accelerating lipid oxidation during storage. Sulfur
volatiles, such as dimethyl disulfide and dimethyl trisulfide, which
are responsible for the irradiation off-odour, were mainly detected
in irradiated meats regardless of species and cooking. Irradiation
off-odour was diminished when meat samples were stored in aerobic conditions for 6 months. Lipid oxidation was an important
quality problem in both precooked irradiated and irradiated
cooked meat during frozen storage. Carbon monoxide was
produced by irradiation and remained in the meat during 6 months
of frozen storage. Irradiating meats after cooking produced
similar lipid oxidation, volatiles and color problems to irradiating
them before cooking. Combination of antioxidants would be
important for the irradiated meats to be stored under aerobic
conditions.
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