Effect of Cooking on Radiation-Induced Chemical
Markers in Beef and Pork during Storage
Abstract: Raw and cooked beef and pork loins were irradiated at 0 or 5 kGy. The radiation-induced marker compounds, such as hydrocarbons, 2-alkylcyclobutanones (2-ACBs), and sulfur volatiles, were determined after 0 and 6 mo
of frozen storage. Two hydrocarbons (8-heptadecene [C17:1 ] and 6,9-heptadecadiene [C17:2 ]) and two 2-ACBs (2dodecylcyclobutanone [2-DCB] and 2-tetradecylcyclobutanone [2-TCB]) were detected only in irradiated raw and
cooked meats. Although precooked irradiated meats produced more hydrocarbons and 2-ACBs than the irradiated
cooked ones, the amounts of individual hydrocarbons and 2-ACBs, such as 8-heptadecene, 6,9-heptadecadiene, 2-DCB,
and 2-TCB, were sufficient enough to detect whether the meat was irradiated or not. Dimethyl disulfide and dimethyl
trisulfide were also determined only in irradiated meats but dimethyl trisulfide disappeared after 6 mo of frozen storage
under oxygen-permeable packaging conditions. The results indicated that 8-heptadecene, 6,9-heptadecadiene, 2-DCB,
2-TCB, and dimethyl disulfide, even though they were decreased with storage, could be used as marker compounds for
the detection of irradiated beef and pork regardless of cooking under the frozen conditions for 6 mo.
Keywords: beef, cooking, hydrocarbons, irradiation, pork, sulfur volatiles, storage, 2-alkylcyclobutanones
Radiation-induced chemical changes such as specific hydrocarbons, 2-ACBs, and sulfur volatiles
may be used as potential identification markers by regulatory authorities to confirm irradiation history of frozen stored
raw or cooked beef and pork.
Practical Application:
Introduction
Food irradiation is one of the effective technologies that can
improve the safety of foods by eliminating disease-causing germs.
Irradiation of raw meats can prevent foodborne diseases and thousands of hospitalizations in the United States every year (CDCP
2005). The U.S. Food and Drug Administration approved irradiation for poultry and red meats to control foodborne pathogens
and extend products’ shelf life (Gants 1998). The approved doses
for fresh and frozen red meats are 4.5 and 7.0 kGy, respectively
(USDA 1999). Many other countries also have approved irradiation to control pathogens and parasites, and extend shelf life of
various food items including red meats and poultry (IAEA 2008).
Since mid-1980s, extensive research for developing detection
methods for irradiated foods has been conducted. Different tests,
which include microbiological screening, electron spin resonance
spectroscopy, thermoluminescence, and monitoring the formation
of long-chain hydrocarbons and 2-alkylcyclobutanones (2-ACBs),
MS 20110973 Submitted 8/9/2011, Accepted 10/24/2011. Authors J.-H. Kwon
and Y. Kwon are with Dept. of Food Science & Technology, Kyungpook Natl. Univ.,
Daegu 702-701, Korea. Author Kausar is with Inst. of Food Science & Nutrition,
Univ. of Sargodha, Sargodha 40100, Pakistan. Author Nam is with Dept. of Animal
Science and Technology, Sunchon Natl. Univ., Suncheon 540-742, Korea. Author Min
is with Dept. of Food Science & Technology, Univ. of Maryland Eastern Shore, Princess
Anne, MD 21853, U.S.A. Authors Lee and Ahn are with Dept. of Animal Science,
Iowa State Univ., Ames, IA 50011-3150, U.S.A. Author Lee is also with Dept.
of Food and Nutrition, Univ. of Wisconsin-Stout, Menomonie, WI 54751, USA.
Author Ahn is also with Dept. of Agricultural Biotechnology, Major in Biomodulation,
Seoul Natl. Univ., Seoul 151-921, Korea. Direct inquiries to author J.-H. Kwon
(E-mail: jhkwon@knu.ac.kr).
R
2012 Institute of Food Technologists
doi: 10.1111/j.1750-3841.2011.02528.x
C
Further reproduction without permission is prohibited
were adopted as standard reference methods for the detection of
irradiated foods by the European Committee for Normalization
(Delincée 2002).
Some chemical changes in foods, which can be used as irradiation indicators or markers, occur during irradiation by free radical
reactions. 2-ACBs such as 2-dodecylcyclobutanone (2-DCB) and
2-tetradecylcyclobutanone (2-TCB) are formed in irradiated fat
or oil by the loss of an electron from acyl-oxygen bond in fatty
acids, followed by a rearrangement process to produce 2-ACBs
specific to their parent fatty acids (Nawar 1986; Stevenson and
others 1990; Stewart 2001). Because 2-DCB and 2-TCB are not
detected in nonirradiated foods, they were used as markers for
detecting irradiated foods (Stevenson and others 1990; Meier and
Stevenson 1993; Stewart and others 2001). These 2-ACBs are extracted using n-hexane or n-pentane along with fat, fractionated
using adsorption chromatography prior to separation using a gas
chromatography (GC) and detection using a mass spectrometer
(MS). Other 2-ACBs such as 2-(tetradec-5 -enyl) cyclobutanone
derived from oleic acid also have been identified in irradiated
foodstuffs (Stewart and others 1998, 2000, 2001).
Hydrocarbons (HC) in fat-containing foods were generated by
the primary and secondary reactions after the chemical bonds in
fatty acids are broken by irradiation. The fatty acid moieties of
triglycerides are mainly broken at alpha and beta positions of carbonyl groups and 2 types of hydrocarbons, which contain 1 (Cn-1)
or 2 (Cn-2:1) less carbon atoms than its parent fatty acids, are
formed (LeTellier and Nawar 1972; Stevenson and others 1990).
Ionizing radiation generates hydroxyl radicals in aqueous
(Thakur and Singh 1994) or oil emulsion systems (O’Connell
and Garner 1983). Hydroxyl radical is the most reactive oxygen
Vol. 77, Nr. 2, 2012 r Journal of Food Science C211
C: Food Chemistry
Joong-Ho Kwon, Youngju Kwon, Tusneem Kausar, Ki-Chang Nam, Byong Rok Min, Eun Joo Lee, and Dong U. Ahn
Radiation-induced markers in beef & pork . . .
C: Food Chemistry
species and can initiate lipid oxidation by abstracting a hydrogen
atom from fatty acyl chain of a polyunsaturated fatty acid and
form a lipid radical. In the presence of oxygen, the lipid radical
rapidly reacts with oxygen to form a peroxyl radical which, in
turn, can extract a hydrogen atom from another fatty acyl chain,
yielding a new free radical that can perpetuate the chain reaction, and a lipid hydroperoxide that can be degraded into various
volatile compounds including aldehydes, ketones, hydrocarbons,
and sulfur compounds, after a series of secondary reactions (Gray
1978; Enser 1987). Some gases such as carbon monoxide, carbon
dioxide, and methane are also produced by reactions between meat
components and free radicals (Nam and Ahn 2002).
Different scientists tried to evaluate the effect of pre- or postcooking treatment on identification of irradiated meat (Fan and
others 2002; Obana and others 2006). However, available information on the chemical changes induced by free radicals in precooked irradiated or irradiated cooked meats is not enough for
general understandings. The objective of this study was to identify
the marker compounds that can be used for detecting irradiated
raw as well as cooked ground beef and pork irradiated before or
after cooking.
decene (C17:1 ), eicosane (C20:5 ) 2-DCB, 2-TCB, and 2-(5 tetradecenyl)cyclobutanone standards were purchased from Fluka
(Sigma-Aldrich, Steinheim, Switzerland) to identify hydrocarbons and 2-ACBs. Fresh meats (beef loin and pork loin with
12% and 4.5% fat, respectively) were purchased from local supermarkets (Ames, Iowa, U.S.A.), ground separately through a
5-mm plate, and vacuum-packaged in an oxygen-impermeable
nylon/polyethylene bags (approximately100 g; O2 permeability,
9.3 mL O2 /m2 /24 h at 0 ◦ C; Koch, Kansas City, Mo., U.S.A.)
within 6 h of purchase.
Cooking and irradiation of meats
Five treatments for each meat species were prepared depending
on cooking and irradiation conditions: (1) nonirradiated raw meat
(uncooked, 0 kGy), (2) irradiated raw meat (uncooked, 5 kGy),
(3) nonirradiated cooked meat (cooked, 0 kGy), (4) precooked
irradiated meat (cooked, 5 kGy), and (5) irradiated cooked meat
(5 kGy, cooked). For cooked irradiated meat, cooking was done in
an 85 ◦ C water bath to an internal temperature of 75 ◦ C. Cooked
and raw meat were repackaged in oxygen permeable nylon bags
(4 × 6 ; Associated Bag Co., Milwaukee, Wis., U.S.A.) and irradiated at 5 kGy using a Linear Accelerator (Circe IIIR, Thomson
Materials and Methods
CSF Linac, St. Aubin, France). The energy and power levels used
Chemicals and meats
were 10 MeV and 10.2 kW, respectively, and the average dose
1-Tetradecene (C14:1 ), pentadecane (C15:0 ), 1-h exadecene rate was 92.0 kGy/min. The max/min ratio was approximately
(C16:1 ), 1,7-hexadecadiene (C16:2 ), heptadecane (C17:0 ), 8-hepta- 1.18. The absorbed dose was assured by 2 alanine dosimeters per
Table 1– Effect of irradiation timing and subsequent storage at −20 ◦ C on the concentrations of radiation-induced hydrocarbons
in cooked beef.
Hydrocarbons
1-Tetradecene(C14:1 )
1-Tetradecene(C14:1 )
Pentadecane(C15:0 )
Pentadecane(C15:0 )
1-Hexadecene(C16:1 )
1-Hexadecene(C16:1 )
6,9-Heptadecadiene(C17:2 )
6,9-Heptadecadiene(C17:2 )
8-Heptadecene(C17:1 )
8-Heptadecene(C17:1 )
n-Heptadecane(C17:0 )
n-Heptadecane(C17:0 )
Raw meat (μg/g fat)
Cooked before IR(μg/g fat)
Storage time
(mo)
0 kGy
5 kGy
0 kGy
5 kGy
Cooked after IR(μg/g fat)
5 kGy
0
6
0
6
0
6
0
6
0
6
0
6
ND
ND
1.61 ± 0.51c,x
1.46 ± 0.03d,x
0.86 ± 0.39d,x
ND
ND
ND
ND
ND
2.88 ± 0.06b,x
0.37 ± 0.03c,y
9.30 ± 0.21b,x
6.37 ± 0.20b,y
7.12 ± 0.16b,x
5.10 ± 0.02c,y
6.74 ± 0.90c,x
4.47 ± 0.55c,y
2.51 ± 0.15a,x
1.82 ± 0.64a,x
7.00 ± 0.21a,x
5.05 ± 0.25b,y
5.43 ± 0.18a,x
3.83 ± 0.42b,y
ND
ND
1.35 ± 0.41c,x
1.04 ± 0.37e,x
1.33 ± 0.73d,x
0.56 ± 0.08d,x
ND
ND
ND
ND
3.44 ± 0.19b,x
0.38 ± 0.19c,y
12.23 ± 0.92a,x
7.35 ± 0.03a,y
14.39 ± 0.96a,x
9.9 ± 0.23a,y
9.91 ± 0.93b,x
5.97 ± 0.36b,y
2.54 ± 0.14a,x
1.98 ± 0.0a,y
6.94 ± 0.40a,x
5.75 ± 0.08a,y
6.18 ± 0.78a,x
5.24 ± 0.98a,x
8.06 ± 0.07c,x
7.58 ± 0.26a,y
7.86 ± 0.06b,x
5.78 ± 0.24b,y
19.616 ± 0.39a,x
15.80 ± 0.25a,y
1.73 ± 0.715b,x
1.49 ± 0.39a,x
4.53 ± 0.75b,x
3.07 ± 0.12c,y
6.17 ± 0.26a,x
5.51 ± 0.53a,x
superscript letters within a row of the same storage day are significantly different (P < 0.05); n = 3.
Different superscript letters within a column are significantly different (P < 0.05).
ND = not detected.
a,b,c,d
Different
x,y
Table 2– Effect of irradiation timing and subsequent storage at −20 ◦ C on the concentrations of radiation-induced hydrocarbons
in cooked pork.
Hydrocarbons
1-Tetradecene(C14:1 )
1-Tetradecene(C14:1 )
Pentadecane(C15:0 )
Pentadecane(C15:0 )
1-Hexadecene(C16:1 )
1-Hexadecene(C16:1 )
6,9-Heptadecadiene(C17:2 )
6,9-Heptadecadiene(C17:2 )
8-Heptadecene(C17:1 )
8-Heptadecene(C17:1 )
n-Heptadecane(C17:0 )
n-Heptadecane(C17:0 )
Raw meat (μg/g fat)
Cooked before IR(μg/g fat)
Storage time
(mo)
0 kGy
5 kGy
0 kGy
5 kGy
Cooked after IR(μg/g fat)
5 kGy
0
6
0
6
0
6
0
6
0
6
0
6
0.42 ± 0.00b,x
ND
0.59 ± 0.00c,x
ND
ND
ND
ND
ND
ND
ND
0.86 ± 0.32c,x
0.20 ± 0.00c,y
5.63 ± 0.3a,x
4.81 ± 0.07a,y
6.13 ± 0.69a,x
5.35 ± 0.37a,x
3.19 ± 0.42a,x
2.89 ± 0.90a,x
3.37 ± 0.18a,x
1.17 ± 0.10c,y
6.25 ± 0.92a,x
4.57 ± 0.29a,y
4.13 ± 0.78a,x
4.12 ± 0.43a,x
0.3744 ± 0.03b,x
ND
1.41 ± 0.01c,x
1.33 ± 0.23d,x
1.93 ± 0.00b,x
1. 80 ± 0.21b,x
ND
ND
ND
ND
1.34 ± 0.3bc,x
0.37 ± 0.04b,c,y
5.50 ± 0.09a,x
4.23 ± 0.04c,y
4.50 ± 0.57b,x
2.97 ± 0.04c,y
3.22 ± 0.65a,x
3.25 ± 0.48a,x
3.51 ± 0.47a,x
1.82 ± 0.02a,y
5.57 ± 0.89a,x
4.11 ± 0.51a,x
1.02 ± 0.41c,x
0.62 ± 0.00bc,x
5.10 ± 0.84a,x
4.47 ± 0.35b,x
5.15 ± 0.69b,x
4.03 ± 0.11b,y
3.12 ± 0.29a,x
1.06 ± 0.00b,y
3.09 ± 0.57a,x
1.55 ± 0.37b,y
6.62 ± 0.56a,x
4.20 ± 0.026a,y
2.16 ± 0.33b,x
0.70 ± 0.08b,y
superscript letters within a column of the same storage day are significantly different (P < 0.05); n = 3.
Different superscript letters within a row are significantly different (P < 0.05).
ND = not detected.
a,b,c,d
Different
x,y
C212 Journal of Food Science r Vol. 77, Nr. 2, 2012
cart and read using a 104 Electron Paramagnetic Resonance Instrument (Bruker Instruments Inc., Billerica, Mass., U.S.A.). For
irradiated cooked meat, raw meats were irradiated first and then
cooked immediately after irradiation using the same conditions as
earlier. Samples were analyzed at 0 d and after 6 mo of storage at
–20 ◦ C under oxygen permeable packaging conditions.
Fatty acid composition
The fat in raw meats was extracted using Folch’s method
(Folch and others 1957). Fatty acid composition was analyzed after methylating fats using BF3 -methanol (14% solution, Supelco,
Bellefonte, Pa., U.S.A.). The fatty acid methyl esters were separated using a gas chromatograph (Model 6890, Hewlett Packard
Co., Wilmington, Del., U.S.A.) equipped with a flame ionization
detector (FID). A split inlet (split ratio, 29:1) was used to inject
samples into an HP-5 capillary column (0.25 mm × 0.25 μm ×
30 m), and ramped oven temperature was used (80 ◦ C for 0.3 min,
increased to 180 ◦ C at 30 ◦ C/min, and increased to 230 ◦ C at
6 ◦ C /min). Inlet and detector temperatures were 180 and 280 ◦ C,
respectively. Helium was the carrier gas at a constant flow of
1.1 mL/min. The flows of detector (FID) air, H2 , and make-up
gas (He) were 300, 30, and 28 mL/min, respectively. Fatty acids
were identified using the retention times of known standards. Relative quantities were expressed as weight percentage of total fatty
acids.
aliquot of extracted fat (1 g) was mixed with an internal standard
(1 mL of n-eicosane, 4 μg/mL in n-hexane) and loaded onto the
column. Hexane (120 mL) was used to elute hydrocarbons. The
eluent was collected and concentrated to 2 mL in a rotary vacuum
evaporator, and further concentrated to 0.5 mL under N2 stream.
For 2-ACBs, extracted fat (0.5 g) was mixed with an internal standard (1 mL 2-cyclohexylcyclohexanone, 1 μg/mL in n-hexane)
and applied to a florisil column, washed with 150 mL of hexane,
and then eluted with 120 mL of diethyl ether/hexane (2:98, v/v)
at a flow rate of 3 mL/min. The eluent was concentrated to 2 mL
using a rotary vacuum evaporator and further concentrated to
0.2 mL using N2 gas.
A GC/MS (Hewlett Packard Co.), with selected ion monitoring mode, was used to analyze hydrocarbons (Nam and others
2011), 2-DCB (m/z 98) and 2-TCB (m/z 112). A 10 ppm of standard solution (5 μL) and samples (10 μL) was withdrawn using
an airtight syringe and injected to a splitless inlet of a GC, separated using a DB-5 column (30.0 m × 0.32 mm i.d., 0.25 m film
thickness, J&W Scientific, Folsom, Calif., U.S.A.), and identified
using a mass selective detector (MSD). Ramped oven temperature was used to separate hydrocarbons. The initial oven temperature was 120 ◦ C and then increased to 175 ◦ C at 10 ◦ C /min
and to 275 ◦ C at 25 ◦ C /min. A constant column flow at
1.5 mL/min was used and the temperature of inlet was set at
250 ◦ C. The ionization potential of MSD (Model 5973, Hewlett
Packard Co.) was 70 eV, and the scan range was 30.1 to 350 m/z.
Identification of hydrocarbons and 2-ACBs was achieved by
comparing the retention time and mass spectral data of samples
with those of the authentic hydrocarbons and 2-ACBs standards
from the Wiley library (Hewlett Packard Co.). The concentration of each hydrocarbon in fat was determined using n-eicosane
(4 μg/mL) or 2-cyclohexylcyclohexanone (1 μg/mL) as the internal standards.
HCs and 2-ACBs
Thirty grams of meat, 300 mL of solvent (hexane/isopropanol,
3:2, v/v), and 50 g of anhydrous sodium sulfate were added in a
500 mL centrifuge bottle and homogenized using a Polytron for
1 min at highest speed to extract fat. Samples were kept overnight
and then centrifuged at 2,000 × g for 20 min at 4 ◦ C. The
supernatant containing fat was collected and the solvent (hexane/isopropanol mixture) was removed using a rotary vacuum
evaporator. The resulting fat was placed in nitrogen (N2 ) filled Sulfur volatile compounds
vials and stored at –20 ◦ C. HCs were separated using a florisil colA dynamic headspace analysis for sulfur volatiles was performed
umn (200 ◦ C 20 mm glass column) packed with 30 g of deactivated through the use of a Solartek 72 Multimatrix-Vial Autosamflorisil and a 1-cm layer of anhydrous sodium sulfate on the top. An pler/Sample Concentrator 3100 (Tekmar-Dohrmann, Cincinnati,
Table 3– Effect of irradiation timing and subsequent storage at −20
2-alkylcyclobutanones in cooked beef.
2-DCB (μg/g fat)
Cooking treatment
Raw meat
Raw meat
Cooked before IR
Cooked before IR
Cooked after IR
◦
C on the concentrations of radiation-induced
2-TCB (μg/g fat)
2-TeCB (μg/g fat)
IR dose (kGy)
0 mo
6 mo
0 mo
6 mo
0 mo
6 mo
0
5
0
5
5
ND
1.93 ± 0.02a,x
ND
1.63 ± 0.69a,x
0.76 ± 0.47b,x
ND
0.96 ± 0.04b,y
ND
1.06 ± 0.06a,x
0.23 ± 0.06c,x
ND
0.51 ± 0.01a,x
ND
0.25 ± 0.18b,x
0.13 ± 0.07b,x
ND
0.14 ± 0.06a,y
ND
0.05 ± 0.03b,x
0.10 ± 0.02a,b,x
1.28 ± 0.35c,x
5.81 ± 0.06a,x
0.67 ± 0.04c,x
4.39 ± 1.51b,x
2.09 ± 0.53c,x
0.55 ± 0.16c,y
2.97 ± 0.02a,y
0.42 ± 0.11c,y
2.76 ± 0.78a,x
1.77 ± 0.20b,x
superscript letters within a column of the same storage day are significantly different (P < 0.05); n = 3.
Different superscript letters within a row are significantly different (P < 0.05).
ND = not detected.
a,b,c
Different
x,y
Table 4– Effect of irradiation timing and subsequent storage at −20
2-alkylcyclobutanones in cooked pork.
2-DCB (μg/g fat)
Cooking treatment
Raw meat
Raw meat
Cooked before IR
Cooked before IR
Cooked after IR
IR dose (kGy)
0
5
0
5
5
0 mo
ND
0.41 ± 0.09a,x
ND
0.45 ± 0.31a,x
0.46 ± 0.13a,x
6 mo
ND
0.08 ± 0.01b,y
ND
0.25 ± 0.16a,x
0.23 ± 0.02a,y
◦
C on the concentrations of radiation-induced
2-TCB (μg/g fat)
0 mo
ND
0.44 ± 0.05a,x
ND
0.65 ± 0.62a,x
0.38 ± 0.05a,x
2-TeCB (μg/g fat)
6 mo
0 mo
6 mo
ND
0.11 ± 0.01a,y
ND
0.42 ± 0.35a,x
0.19 ± 0.01a,y
0.25 ± 0.06
0.82 ± 0.20a,x
0.30 ± 0.01a,x
0.88 ± 0.36a,x
0.54 ± 0.48a,x
a,x
0.22 ± 0.02c,x
0.40 ± 0.02c,y
0.27 ± 0.22c,x
0.68 ± 0.32b,x
0.95 ± 0.01a,x
superscript letters within a column of the same storage day are significantly different (P < 0.05); n = 3.
Different superscript letters within a row are significantly different (P < 0.05).
ND = Not detected.
a,b,c
Different
x,y
Vol. 77, Nr. 2, 2012 r Journal of Food Science C213
C: Food Chemistry
Radiation-induced markers in beef & pork . . .
Radiation-induced markers in beef & pork . . .
C: Food Chemistry
Ohio, U.S.A.) connected to a GC/MS (HP 6890/HP 5973, an irradiation marker for beef. 8-Heptadecene (C17:1 ) and 6,9Hewlett-Packard Co.) according to the method of Ahn and others heptadecadiene (C17:2 ), derived from oleic acid and linoleic acid,
respectively, were found at high concentrations in irradiated meats
(2001).
but not detected in both nonirradiated raw and cooked beef as
well as pork (Table 1 and 2). Therefore, 8-heptadecene and 6,9Statistical analysis
The experiments, performed in 4 replications, were designed to heptadecadiene can be used as markers for irradiated raw and
monitor the radiation-induced markers, such as fat-derived hydro- cooked beef and pork. New hydrocarbons can also be formed by
carbons and 2-ACBs, along with carbon monoxide production and heating. In vegetable oils, long-chain hydrocarbons were found afsulfur volatiles from irradiated meats. Analysis of variance was done ter heating or frying (Nawar 1977). Long-chain hydrocarbons are
using the generalized linear model procedure of SAS software (SAS also found in animal products such as roasted chickens (Noleau and
Institute Inc. 1995). Student–Newman–Keul’s multiple range test Toulemonde 1987). Although cooked meats before and after irrawas used to compare the mean values of the treatments. Mean diation had a significantly higher number of hydrocarbons than raw
meat, 8-heptadecene and 6,9-heptadecadiene were not detected
values and standard error of the mean were reported (P < 0.05).
in cooked nonirradiated meats. Although the concentrations of
hydrocarbons decreased during storage, the radiation-induced hyResults and Discussion
drocarbons were still detectable even after 6 mo of frozen storage,
Fatty acid composition
with higher stability in 8-heptadecene than in 6,9-heptadecadiene.
The fatty acid of raw beef was composed of 41.71% oleic acid, Long-term stability of radiolytic hydrocarbons was also found in
28.62% palmitic acid, 11.21% stearic acid, 4.68% linoleic, and various other meat samples (Merritt and others 1978; Schreiber
1.44% arachidonic acid. Raw pork had 44.60% oleic acid, 23.26% and others 1994).
palmitic acid, 12.65% linoleic acid, 9.12% stearic acid, and 0.97%
arachidonic acid. Irradiation at 5 kGy before or after cooking had 2-ACBs
no effect on the fatty acid composition of meat. Our results were
2-DCB and 2-TCB were detected only in irradiated beef and
in good agreement with findings of Alfaia and others 2007 in pork regardless cooking treatment (Table 3 and 4). The stability
frozen lamb meat. However, irradiation-induced little changes in of radiation-induced 2-ACBs after cooking treatment was also
fatty acid composition of raw or cooked meats were reported by reposted by Obana and others (2006). The concentration of 2Hau and others (1992).
DCB was higher than that of 2-TCB since palmitic acid, the
precursor of 2-DCB, was more abundant than stearic acid, the
HCs
precursor of 2-TCB, in meats (Nawar 1986; Stevenson and others
The amounts of radiation-induced hydrocarbons in beef and 1990; Stewart 2001). This result agrees with that of Stevenson
pork increased in upon irradiation at 5 kGy (Table 1 and 2). and others (1993) who used 2-DCB and 2-TCB as irradiation
Cooking newly produced 1-hexadecene in pork but found in markers in liquid whole egg. Among the 2-ACBs, 2-TCB was
nonirradiated raw beef at 0 mo storage, which were significantly present at the highest level in both irradiated beef and pork but
increased by irradiation. Thus, 1-hexadecene cannot be used as was also detected in nonirradiated meats. 2-ACBs were reported
Table 5–Effect of irradiation timing and subsequent storage at −20 ◦ C on the concentrations of radiation-induced sulfur compounds
in cooked beef.
Dimethyl sulfide
(total ion counts ×
104 )
Cooking treatment
Raw meat
Raw meat
Cooked before IR
Cooked before IR
Cooked after IR
SEM
IR dose (kGy)
0
5
0
5
5
0 mo
721
1064
790
0
662
537
6 mo
0
0
0
0
0
0
Dimethyl disulfide
(total ion counts ×
104 )
0 mo
b
0
2833a,b
0b
2872a,b
5933a
945
6 mo
0c
2054b
0c
2255b
3835a
424
Dimethyl trisulfide
(total ion counts ×
104 )
0 mo
b
0
0b
0b
0b
485a
149
6 mo
0
0
0
0
0
0
Different superscript letters within a column of the same storage day are significantly different (P < 0.05); n = 3.
SEM = standard error of mean.
a,b
Table 6–Effect of irradiation timing and subsequent storage at −20 ◦ C on the concentrations of radiation-induced sulfur compounds
in cooked pork.
Dimethyl sulfide
(total ion counts ×
104 )
Cooking treatment
Raw meat
Raw meat
Cooked before IR
Cooked before IR
Cooked after IR
SEM
IR dose (kGy)
0
5
0
5
5
0 mo
907
2135
573
249
815
493
6 mo
0
0
0
0
0
0
Dimethyl disulfide
(total ion counts ×
104 )
0 mo
b
0
3394a,b
0b
4317a
3405a,b
828
Different superscript letters within a column of the same storage day are significantly different (P < 0.05); n = 3.
SEM = standard error of mean.
a,b
C214 Journal of Food Science r Vol. 77, Nr. 2, 2012
6 mo
0
136
0
44
690
247
Dimethyl trisulfide
(total ion counts ×
104 )
0 mo
b
0
0b
0b
489a
535a
59
6 mo
0
0
0
0
0
0
in nonirradiated cashew nut samples by Variyar and others (2008). References
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ACB compounds because it was detected only in irradiated meats
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Sulfur volatile compounds
Table 5 and 6 show the representative sulfur volatiles (dimethyl
sulfide, dimethyl disulfide, and dimethyl trisulfide) detected in
beef and pork, respectively. The amount of dimethyl disulfide was
significantly higher in irradiated meats than nonirradiated ones.
Dimethyl disulfide and dimethyl trisulfide were not found in nonirradiated meats but present in irradiated ones confirming the
results earlier reported by Fan and others (2002). This result was
in agreement with that of sensory evaluation where sulfur-related
odor/flavor was significantly increased in irradiated meats (Zhu
and others 2003). Due to low threshold for odor detection, even
small amounts of these sulfur compounds are important for irradiation off-odor (Ahn and others 2001). The ratios among sulfur
volatiles in meat also changed during storage, which should have
significant impact on the overall odor characteristics of irradiated
meat because each sulfur compound has its own characteristic odor
notes (Girard and Durance 2000). Irradiated pork produced more
sulfur volatiles than irradiated beef and most of these compounds
were disappeared more apparently in pork than in beef after 6 mo
of storage at –20 ◦ C. Nevertheless, dimethyl disulfide was still detectable in all meats after 6 mo of frozen storage under oxygen
permeable packaging conditions (Table 5 and 6).
Conclusions
Two hydrocarbons, 8-heptadecene (C17:1 ) and 6,9heptadecadiene (C17:2 ) and two 2-ACBs, 2-DCB and 2-TCB
were detected only in irradiated beef and pork regardless of
cooking treatment. Although hydrocarbons and 2-ACB levels
were decreased during storage, detectable levels of 8-heptadecene,
6,9-heptadecadiene, 2-DCB, and 2-TCB were still remaining
and they could serve as indicators for irradiated raw and cooked
beef and pork. Dimethyl disulfide was only detected in irradiated
beef and pork samples regardless of cooking treatment and after
frozen-stored for 6 mo under oxygen permeable packaging
conditions, indicating that it also could be used as an irradiation
marker for raw and frozen cooked beef and pork.
Acknowledgments
This study was supported jointly by Sunchon Natl. Univ.,
Kyungpook Natl. Univ., and WCU (World Class Univ.) program (R31–10056) through the Natl. Research Foundation
of Korea funded by the Ministry of Education, Science and
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