JFS: Food Chemistry and Toxicology
Prevention of Pinking, Off-odor,
and Lipid Oxidation in Irradiated
Pork Loin Using Double Packaging
K.C. NAM, B.R. MIN, S.C. LEE , J. CORDRAY , AND D.U. AHN
Food Chemistry and Toxicology
ABSTRACT: Lipid oxidation, color, volatiles, and sensory evaluation of double-packaged pork loin were determined
to establish a modified packaging method that can improve the quality of irradiated pork loins. Vacuum-packaged
irradiated samples produced dimethyl sulfide and dimethyl disulfide responsible for irradiation off-odor, whereas
lipid oxidation was promoted under aerobic conditions. Exposing double-packaged irradiated pork to aerobic
conditions for 1 to 3 d was effective in controlling both lipid oxidation and irradiation off-odor, regardless of
packaging sequence. Sensory panels could distinguish the decrease in irradiation off-odor intensities by modifying
the packaging method. However, carbon monoxide heme pigments, responsible for the increased redness by irradiation, were not effectively controlled by double packaging alone.
Keywords: double packaging, irradiation, lipid oxidation, off-odor, pork loin
Introduction
C
onsumers and regulatory agencies are well aware of the dangers of enteropathogenic Escherichia coli, Salmonella, and Listeria to human health. Irradiation provides the best method to control these pathogens in raw meat. The quality change in meat by irradiation, however, is a concern to the meat industry and to
consumers. Pink color (Millar and others 1995; Nam and Ahn 2002)
and off-odor (Patterson and Stevenson 1995; Ahn and others 2001)
in poultry meat produced by irradiation persists throughout the
storage period under vacuum conditions. The major volatile compounds responsible for off-odor in irradiated meats are sulfur compounds. Irradiation produces sulfur compounds via radiolytic degradation of sulfur-containing amino acids, such as methionine and
cysteine (Jo and Ahn 2000; Ahn 2002). The prevention of pink color
defects and off-odor in poultry and pork is critical for the use of irradiation in those meats because consumers associate the presence of a pink color with undercooked or contaminated meat, and
off-odor with the formation of undesirable chemical compounds by
irradiation.
The color and odor changes in irradiated meat are highly dependent on packaging conditions. Under aerobic packaging conditions,
most of the sulfur compounds produced by irradiation disappeared and color returned to normal after a few days of storage in
irradiated turkey breast (Nam and Ahn 2003). Lipid oxidation, however, significantly increased when meat was irradiated and stored
in aerobic packaging conditions (Ahn and others 2001).
Therefore, an appropriate use of aerobic and vacuum-packaging conditions (so-called double-packaging) can be effective
in minimizing lipid oxidation and off-odor volatiles in irradiated
pork loin during storage, which also may affect pink color in irradiated pork. Two double-packaging strategies are devised: In
MS 20030625 Submitted 10/31/03, Revised 12/9/03, Accepted 12/19/03. Authors Nam, Min, Cordray, and Ahn are with the Animal Science Dept., Iowa
State Univ., Ames, IA 50011-3150. Author Lee is with Dept. of Food Science
and Biotechnology, Kyungnam Univ., Korea. Direct inquiries to author Ahn
(E-mail: duahn@iastate.edu).
FCT214 JOURNAL OF FOOD SCIENCE—Vol. 69, Nr. 3, 2004
Published on Web 3/25/2004
model nr 1, pork loins were double-packaged (aerobic bag inside
and vacuum bag outside) and irradiated. A few days after irradiation, the outer vacuum bag was removed and then stored. In
model nr 2, loins were aerobically packaged and irradiated. A few
days after irradiation, the loins were vacuum-packaged and then
stored.
The objective of this study was to determine the effect of doublepackaging conditions on lipid oxidation, volatiles, and color of irradiated pork loins during refrigerated storage. This study can provide information that can control the quality defects in irradiated
pork because controlling pink color and off-odor production can
improve consumer acceptance of irradiated pork.
Materials and Methods
Sample preparation
Pork loin (longissimus dorsi) muscles from 8 different animals
were purchased from a local packing plant and all surface fat was
trimmed. The lean muscles were sliced into 2-cm-thick steaks and
packaged as follows: (1) oxygen-permeable bags (polyethylene,
4 × 6, 2 mil; Assoc. Bag Co., Milwaukee, Wis., U.S.A.); (2) oxygen-impermeable vacuum bags (nylon/polyethylene, 9.3 mL O2/m2/24 h
at 0 °C; Koch, Kansas City, Mo., U.S.A.); (3) double-packaged: pork
loins were individually packaged in oxygen-permeable bags 1st,
and then a number of aerobically packaged loins were vacuumpackaged in a larger oxygen-impermeable bag. The packaged meat
samples were irradiated at 2.5 kGy using a linear accelerator (Circe
IIIR; Thomson CSF Linac, Saint-Aubin, France) with 10 MeV of energy, 10.2 kW of power level, and 88.9 kGy/min of average dose rate.
For double-packaging model nr 1, the outer vacuum bags were
removed after 3 d (V3/A7), 5 d (V5/A5), 7 d (V7/A3), or 9 d (V9/A1)
of storage, respectively, during the 10 d of storage at 4 °C. Therefore, 7 different treatments consisted of nonirradiated vacuumpackaged, irradiated aerobically-packaged, irradiated vacuumpackaged, and 4 irradiated double-packaged pork. For
double-packaging model nr 2, aerobically packaged and irradiated
loins were stored at 4 °C for 1 d, 3 d, 5 d, or 7 d, and then vacuum© 2004 Institute of Food Technologists
Further reproduction without permission is prohibited
packaged (A1/V9, A3/V7, A5/V5, or A7/V3, respectively). Nonirradiated vacuum-packaged, irradiated under aerobic, and irradiated under vacuum conditions were also prepared as controls. Lipid
oxidation, color, gas, oxidation-reduction potential, and volatiles of
the samples were determined after 0 d and 10 d of storage. Sensory
evaluation was conducted at 10 d.
flows were 400 and 35 mL/min, respectively. The compounds detected were identified using standard gases (CO; Aldrich, Milwaukee, Wis., U.S.A.; CH4 and CO2; Praxair, Danbury, Conn., U.S.A.). An
integrated peak area was converted to a concentration (ppm) in the
headspace (14 mL) of 10 g meat from the concentration of CO2 in air
(330 ppm).
2-Thiobarbituric acid-reactive substances
Volatiles
Lipid oxidation was determined by a 2-thiobarbituric acid–reactive substances (TBARS) method (Ahn and others 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, N.Y., U.S.A.)
for 15 s at high speed. The meat homogenate (1 mL) was transferred
to a disposable test tube (13 × 100 mm), and 50 ␮L butylated hydroxytoluene (7.2% in ethanol) and 2 mL of thiobarbituric acid/
trichloroacetic acid (20 mM TBA and 15%, w/v, TCA) solution were
added. The mixture was vortex-mixed and then incubated in a
90 °C water bath for 15 min. After cooling, the samples were vortexmixed and centrifuged at 3000 × g for 15 min. The absorbance of
the resulting upper layer was read at 531 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.
A dynamic headspace analysis was performed using a Solartek
72 Multimatrix-Vial Autosampler/Sample Concentrator 3100 (Tekmar-Dohrmann, Cincinnati, Ohio, U.S.A.) connected to a gas chromatograph-mass spectrometer (GC-MS) (HP 6890/HP 5973,
Hewlett-Packard Co.) according to the method of Ahn and others
(2001). Minced sample (3 g) was placed in a 40-mL vial, He (40 psi)
was flushed for 3 s, and a Teflon fluorocarbon resin/silicone septum
(I-Chem Co.) was capped airtight. 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 He (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 inner dia, 1.4 ␮m nominal), an HP-1 column (52.5 m,
0.25-mm inner dia, 0.25 ␮m nominal), and an HP-Wax column (7.5
m, 0.250-mm inner dia, 0.25 ␮m 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. After that, the oven temperature was increased to 15 °C at 2.5 °C per
min, increased to 45 °C at 5 °C per min, increased to 110 °C at 20 °C
per min, and then increased to 170 °C at 10 °C per min and held for
2.25 min at that temperature. Constant column pressure at 20.5 psi
was maintained. The ionization potential of mass spectrometer (MS)
was 70 eV, and the scan range was 19.1 to 350 m/z. Identification of
volatiles was achieved by the Wiley library (Hewlett-Packard Co.).
The area of each peak was integrated using ChemStationTM software (Hewlett-Packard Co.) and the total peak area (total ion
counts × 104) was reported as an indicator of volatiles generated
from the samples.
Color measurement
CIE color values were measured on the sample surface using a
LabScan colorimeter (Hunter Associate Labs, Inc., Reston, Va.,
U.S.A.) that had been calibrated against black and white reference
tiles covered with the same packaging materials as used for samples. The CIE L* (lightness), a* (redness), and b* (yellowness) values were obtained by an illuminant A (light source). Two random
readings from both top and bottom locations on a sample surface
were used for statistical analysis.
Oxidation-reduction potential
A pH/ion meter (Accumet 25; Fisher Scientific, Fair Lawn, N.J.,
U.S.A.) was used to measure oxidation-reduction potential (ORP).
A platinum electrode filled with an electrolyte solution (4 M KCl
saturated with AgCl) was tightly inserted into the center of the
block of meat sample. To minimize the effect of air, the smallest
pore possible was made in the sample by a cutter before inserting
the electrode. A temperature-reading sensor was also inserted to
compensate for the effect of temperature. ORP readings (mV )
were recorded at exactly 2 min after inserting the electrode into a
sample.
Gas
The method of Nam and Ahn (2002) was modified to detect gases in meat samples. Minced meat sample (10 g) was placed in a 24mL screw-cap glass vial with a Teflon® fluorocarbon resin/silicone
septum (I-Chem Co., New Castle, Del., U.S.A.). The vial was microwaved at 1.55 kW for 10 s to release gas compounds from the meat.
After 5 min of cooling in room temperature, the headspace gas (200
␮L) was withdrawn using an airtight syringe and injected into a
split inlet (9:1) of a gas chromatograph (GC; HP 6890; Hewlett Packard Co., Wilmington, Del., U.S.A.). A Carboxen-1006 Plot column (30
m × 0.32-mm inner dia; Supelco, Bellefonte, Pa., U.S.A.) was used
and an oven temperature was programmed (initial temperature, 80
°C; increased to 120 °C at 20 °C/min). Helium was the carrier gas at
a constant flow of 1.8 mL/min. A flame-ionizing detector connected to a nickel catalyst (Hewlett Packard Co.) was used for detection
and the temperatures of inlet, detector, and nickel catalyst were set
at 130 °, 280 °, and 375 °C, respectively. Detector air and hydrogen
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Sensory evaluation
A 12-member sensory panel evaluated the intensity of off-odor.
Training sessions were conducted to familiarize panelists with the
irradiation off-odor and rancid odor. Panelists were trained with
meat samples irradiated at high dose (10 kGy) and containing specific chemical compounds found in the volatiles of previous studies. Samples (3 g) stored for 10 d were placed in a coded 40-mL sample vial and capped with a septum (I-Chem Co.). The samples were
incubated for 1 h at 22 °C before serving. According to the modified
method of Jones and others (1989), 4 different samples with the
same packaging method were presented to each panelist in isolated booths at each separate session. Panelists were instructed to
smell the samples at random and to record the intensity of irradiation off-odor and rancid odor on a 15-cm line scale anchored from
“not detectable” to “strongly intense.”
Statistical analysis
The experiment was a completely randomized design and 7 different treatments were compared with 4 replications. Data were
analyzed by the procedure of generalized linear model using SAS
software (SAS Inst. 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).
Vol. 69, Nr. 3, 2004—JOURNAL OF FOOD SCIENCE
FCT215
Food Chemistry and Toxicology
Prevention of pinking . . .
Prevention of pinking . . .
Table 1—2-Thiobarbituric acid–reactive substances (TBARS) values of irradiated raw pork loin with different packaging conditions during refrigerated storage (expressed as mg of malondialdehyde per kg of meat)a
Storage
0d
10 dc
10 dd
SEM
Irradiated
Nonirradiated
Vacuum
Aerobic
V3/A7b
V5/A5b
V7/A3b
V9/A1b
Vacuum
SEM
0.12cy
0.15ex
0.15ex
0.01
0.23ay
0.44ax
0.46ax
0.01
0.21ay
0.33cx
0.38bx
0.01
0.21az
0.37bx
0.29cy
0.01
0.21ay
0.31cdx
0.22dy
0.01
0.21ay
0.28dx
0.24dy
0.01
0.16b
0.17e
0.17e
0.01
0.01
0.01
0.01
a Means with different letters (a–e) within a row are significantly different (P < 0.05), n = 4. Means with different letters (x–z) within a column are significantly
different ( P < 0.05). SEM = standard error of the means.
b Vm/An: Stored under vacuum and aerobic conditions for m days and n days,respectively.
c Double-packaging model nr 1: vacuum-packaged for m days and then aerobically packaged for n days.
d Double-packaging model nr 2: aerobically packaged for m days and then vacuum-packaged for n days.
Food Chemistry and Toxicology
Table 2—a* values of irradiated raw pork loin with different packaging conditions during refrigerated storagea
Nonirradiated
Storage
Vacuum
0d
10 dc
10 dd
SEM
6.6c
7.0c
6.1c
0.5
Irradiated
Aerobic
V3/A7b
V5/A5b
V7/A3b
V9/A1b
Vacuum
SEM
8.2b
8.9b
8.7b
0.4
11.1ax
9.0by
8.4by
0.5
11.2ax
10.9ax
8.1by
0.5
10.7a
10.8a
9.2ab
0.5
10.5ax
10.1abx
8.5by
0.5
10.6a
10.0ab
10.1a
0.4
0.4
0.4
0.4
a Means with different letters (a–c) within a row are significantly different ( P < 0.05), n = 4. Means with different letters (x,y) within a column are significantly
different ( P < 0.05). SEM = standard error of the means. b Vm/An: Stored under vacuum and aerobic conditions for m days and n days, respectively.
c Double-packaging model nr 1: vacuum-packaged for m days and then aerobically packaged for n days.
d Double-packaging model nr 2: aerobically packaged for m days and then vacuum-packaged for n days.
Table 3—ORP of irradiated raw pork loin with different packaging conditions during refrigerated storagea
Nonirradiated
Storage
Vacuum
Irradiated
Aerobic
V3/A7b
V5/A5b
V7/A3b
V9/A1b
Vacuum
SEM
0a
21a
9a
10
–202by
–8abx
4ax
23
–202by
–17abx
–40bx
21
–202by
–26abcx
–43bx
18
–202by
–61bcx
–41bx
16
–225by
–67bcx
–69bx
7
21
14
10
(mV)
0d
10 dc
10 dd
SEM
–43a
–80c
–55b
11
a Means with different letters (a–c) within a row are significantly different ( P < 0.05), n = 4. Means with different letters (x,y) within a column are significantly
different (P < 0.05). ORP = oxidation-reduction potential; SEM = standard error of the means.
b Vm/An: Stored under vacuum and aerobic conditions for m days and n days, respectively.
c Double-packaging model nr 1: vacuum-packaged for m days and then aerobically packaged for n days.
d Double-packaging model nr 2: aerobically packaged for m days and then vacuum-packaged for n days.
Results and Discussion
Lipid oxidation
Irradiation increased TBARS, but vacuum conditions prevented
lipid oxidation of pork loin (Table 1). The TBARS values of aerobically packaged pork loin were much higher than those of the vacuum-packaged meat after 10 d of storage. The TBARS values of double-packaged meats ranked between the aerobically and the
vacuum-packaged ones. Double-packaged loins with model nr 2
(aerobically then vacuum-packaged) had lower TBARS values than
those with model nr 1 (vacuum-packaged and then aerobically
packaged), showing that lipid oxidation was accelerated as storage
time increased. During the refrigerated storage, exposed time to
aerobic conditions was the most critical factor determining the degree of lipid oxidation, and the TBARS values of pork loins at day 10
were proportional to the days under aerobic conditions. Thus, lipid
oxidation can be a concern in irradiated meat when it is only aerobically packaged.
Color changes
Irradiation changed the color of raw pork loin reddish pink, as
FCT216
JOURNAL OF FOOD SCIENCE—Vol. 69, Nr. 3, 2004
indicated by the colorimeter values (Table 2). The increase in redness (a* values) by irradiation was more distinctive in vacuumpackaged pork loins than in aerobically packaged ones. Therefore,
packaging conditions were important in determining color changes
in pork loin during the irradiation process. The redness of irradiated pork loin was very stable during the 10-d refrigerated storage
irrespective of packaging method. At day 10, the a* values of irradiated pork loins were significantly higher than those of nonirradiated pork. A few double-packaged pork loins (A3/V7, A5/V5) had
significantly lower a* values than irradiated vacuum-packaged ones
during storage, but the values were still higher than those of nonirradiated vacuum-packaged control. Therefore, the double-packaging method alone was not enough to control redness in pork loin
induced by irradiation. L* values in pork loins were little influenced
by irradiation, and b* values showed an increasing trend but the
results were inconsistent (data not shown).
Nam and Ahn (2002) reported that the color of irradiated turkey
breast became pinker due to carbon monoxide–myoglobin complex
formation, which was induced by the production of carbon monoxide and reducing conditions by irradiation. This mechanism of color
changes in irradiated turkey breast can be similarly applied to that
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Prevention of pinking . . .
Table 4—Gas production of irradiated raw pork loin with different packaging conditions during refrigerated storagea
Nonirradiated
Vacuum
Carbon monoxide (ppm)
0d
0b
10 dc
0c
10 dd
0c
SEM
0
Methane (ppm)
0d
0b
10 dc
0c
10 dd
0b
SEM
0
Carbon dioxide (%)
0d
3.1ax
10 dc
1.6bcy
d
10 d
2.5ax
SEM
0.4
Irradiated
Aerobic
V3/A7b
V5/A5b
V7/A3b
V9/A1b
Vacuum
SEM
121ax
84aby
50by
13
123ax
66by
56by
6
123ax
86aby
80aby
6
123ax
108abx
65by
8
123a
114a
117a
13
121ax
107abxy
95aby
9
8
11
11
4b
4c
0b
1
38ax
3cy
0by
2
38ax
4cy
0by
1
38ax
5cy
0by
2
38ax
14by
0bz
2
41ax
49ax
24ay
2
2
1
1
1.3bx
0.8cxy
0.6by
0.2
3.1ax
0.7cy
0.7by
0.3
3.1ax
0.9cy
0.7by
0.3
3.1ax
1.5bcy
0.5bz
0.2
3.1ax
2.3abxy
1.4by
0.2
3.4a
2.8a
3.2a
0.4
0.3
0.2
0.5
a Means with different letters (a–c) within a row are significantly different ( P < 0.05), n = 4. Means with different letters (x,y) within a column are significantly
different ( P < 0.05). SEM = standard error of the means.
b Vm/An: Stored under vacuum and aerobic conditions for m days and n days, respectively.
c Double-packaging model nr 1: vacuum-packaged for m days and then aerobically packaged for n days.
d Double-packaging model nr 2: aerobically packaged for m days and then vacuum-packaged for n days.
of irradiated pork loin because the contents of heme pigments in
those muscles are relatively low. Irradiation decreased the ORP of
pork loin under vacuum-packaged conditions (Table 3). Swallow
(1984) reported that hydrated electrons, radiolytic free radicals,
could be produced by irradiation and act as a very powerful reducing agent. However, the ORP values of irradiated pork loins increased after 10 d in contrast to the decrease in nonirradiated meat,
showing that stronger oxidizing conditions were generated in irradiated meat by oxidizing free radicals such as superoxide and hydroperoxyl radical during storage (Woods and Pikaev 1994).
Irradiation produced a few gas compounds ( Table 4), one of
which was carbon monoxide that could be a ligand of heme pigments in irradiated pork loin and thus increase redness. The production of carbon monoxide was little influenced by packaging
conditions regardless of storage, indicating that most of the carbon
monoxide produced was bound to heme pigments in meat
throughout storage.
Off-odor volatiles
Many new volatile compounds were generated and a few volatiles already present in nonirradiated pork loins increased by irradiation (Table 5). The amount of total volatiles produced in irradiated pork loin was 3 times higher than that of the nonirradiated
control. At 0 d, sulfur (S)-containing volatiles, 2-propanone, and
ethanol were the most predominant volatiles in irradiated pork
loin. Among the detected S-volatiles, methanethiol, dimethyl sulfide, methylthio ethane, and dimethyl disulfide could be responsible for the characteristic irradiation off-odor. Ahn and others
(2000a) reported that S-containing volatiles, such as 2,3-dimethyl
disulfide, produced by the radiolytic degradation of sulfur amino
acids, were responsible for the off-odor in irradiated pork and their
amounts were highly dependent upon irradiation dose. They also
assumed that the off-odor volatiles in irradiated pork were the result of compounding effects of volatiles from lipid oxidation and
radiolysis of various amino acid side chains.
The amounts of S-volatiles in irradiated pork loin were highly
dependent on packaging conditions. Higher amounts of S-volatiles
were found in vacuum-packaged or double-packaged pork loin than
in aerobically packaged ones, indicating that considerable amounts
of S-compounds were evaporated under aerobic conditions during
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Table 5—Volatile compounds of irradiated raw pork loin with
different packaging conditions at day 0a
Compound
NonirIrradiated
radiated
Vacuum Aerobic Double Vacuum SEM
Total ion counts × 104
Acetaldehyde
324
Methanethiol
0c
Pentane
0c
Dimethyl sulfide
0b
2-Propanone
1169
Hexane
0b
Ethanol
3317
Methylthio ethane
0
2-Propanol
229
2-Butanone
74c
Benzene
0
1-Heptene
0
Heptane
0
2-Pentanone
36
Dimethyl disulfide
37c
Toluene
0
Octane
30
Hexanal
0
Total
4894b
496
887c
526a
610b
6344
723a
2184
0
777
930a
41
111
373
0
773c
185
582
65
15207a
648
3886a
349b
2771a
3155
232b
1056
85
147
350b
83
51
63
121
1761b
0
125
0
14241a
755
2238b
349b
2345a
3473
217b
1457
406
340
417b
16
53
82
0
2678a
0
201
0
14274a
179
342
27
382
2435
132
934
182
360
97
33
40
190
41
290
70
187
32
1457
a Means with different letters (a–c) within a row are significantly different ( P <
0.05), n = 4. SEM = standard error of the means.
the process of irradiation and post-irradiation handling. For the
meat that will be consumed fresh (lipid oxidation is not a problem),
therefore, aerobic packaging is more beneficial than vacuum-packaging in terms of reducing irradiation off-odor. The amounts of dimethyl sulfide and dimethyl disulfide in aerobically packaged pork
loin were only 26% and 29% of the vacuum-packaged one, respectively. Lipid oxidation products in irradiated pork loin at 0 d were
minimal, and only aerobically packaged pork loin had a trivial
amount of hexanal.
After 10 d of refrigerated storage, the volatiles profile of irradiated pork loin was highly dependent on packaging conditions (Tables 6 and 7). The greatest amounts of total volatiles were detected in vacuum-packaged pork loin because many S-volatiles still
Vol. 69, Nr. 3, 2004—JOURNAL OF FOOD SCIENCE
FCT217
Food Chemistry and Toxicology
Storage
Prevention of pinking . . .
Table 6—Volatile compounds of irradiated raw pork loin with double-packaging model 1 at day 10a
Compound
Nonirradiated
Vacuum
Irradiated
Aerobic
V3/A7 b
V5/A5 c
V7/A3 d
V9/A1 e
Vacuum
SEM
997a
1790
0b
3012a
0b
221
390a
127
90
65
0b
0b
45
120a
603
45
169a
0b
7674a
597ab
1673
0b
2784a
0b
245
203b
52
52
63
0b
0b
45
103a
653
35
122ab
0b
6627a
564ab
1617
0b
743b
0b
234
204b
60
30
41
0b
0b
45
56ab
573
45
31bc
0b
4243b
613ab
1713
0b
560b
0b
285
296b
91
31
57
0b
0b
91
87a
551
102
57bc
0b
4534b
450ab
1548
0b
317b
37b
275
254b
41
28
29
62b
387b
164
0b
337
0
63bc
54b
4046b
367ab
1958
0b
220b
133a
274
221b
33
0
47
268a
1108a
155
0b
349
0
0c
246a
5379ab
141
189
18
357
24
20
24
35
22
16
28
154
47
18
97
28
21
33
729
104
Food Chemistry and Toxicology
Total ion counts ×
Pentane
2-Propanone
Carbon disulfide
Hexane
Dimethyl sulfide
2-Propanol
2-Butanone
1-Heptene
Heptane
2-Pentanone
S-methyl ethanethioate
Dimethyl disulfide
Toluene
1-Octene
Octane
2-Octene
Hexanal
Dimethyl trisulfide
Total
38b
1388
300a
412b
0b
197
0c
0
0
0
0b
0b
49
0b
237
0
0c
0b
2621c
a Means with different letters within a row are significantly different (P < 0.05),
b Vacuum-packaged for 3 d then aerobically packaged for 7 d.
c Vacuum-packaged for 5 d then aerobically packaged for 5 d.
d Vacuum-packaged for 7 d then aerobically packaged for 3 d.
e Vacuum-packaged for 9 d then aerobically packaged for 1 d.
n = 4.
Table 7—Volatile compounds of irradiated raw pork loin with double-packaging model nr 2 at day 10a
Nonirradiated
Vacuum
Compound
Irradiated
Aerobic
A7/V3 b
A5/V5 c
A3/V7 d
A1/V9 e
Vacuum
SEM
527a
1810
0b
367bc
0b
307a
107
21
62
53ab
0b
0b
192
30
1086
31b
53ab
0b
4646ab
345a
1958
0b
269bc
133a
274ab
40
0
28
47ab
268a
1108a
155
28
820
297a
0b
246a
5883a
69
189
4
111
24
20
41
15
22
16
28
154
47
23
275
33
24
33
823
104
Total ion counts ×
Pentane
2-Propanone
Carbon disulfide
Hexane
Dimethyl sulfide
2-Propanol
2-Butanone
1-Heptene
Heptane
2-Pentanone
S-methyl ethanethioate
Dimethyl disulfide
Toluene
1-Octene
Octane
2-Octene
Hexanal
Dimethyl trisulfide
Total
a Means with different letters
b Aerobically packaged for 7
c Aerobically packaged for 5
d Aerobically packaged for 3
e Aerobically packaged for 1
58b
1388
45a
412b
0b
197b
0c
0
0
0b
0b
0b
49
0
616
219a
0b
0b
2986c
645a
1790
0b
3012a
0b
221ab
34
0
90
65ab
0b
0b
45
19
835
0b
130a
0b
6886a
601a
1650
0b
612b
0b
248ab
115
35
33
102a
0b
0b
188
35
1163
0b
110a
0b
4892b
524a
1610
0b
313bc
0b
249ab
42
0
28
70ab
0b
0b
64
0
831
18b
102a
0b
3851b
(a–c) within a row are significantly different (P < 0.05), n = 4. SEM = standard error of the means.
d then vacuum-packaged for 3 d.
d then vacuum-packaged for 5 d.
d then vacuum-packaged for 7 d.
d then vacuum-packaged for 9 d.
remained under vacuum conditions. Dimethyl disulfide was the
most predominant volatile compound in vacuum-packaged pork
loins. No S-volatiles were detected in most double-packaged pork
loins. S-volatiles such as dimethyl disulfide, dimethyl trisulfide,
and S-methyl ethanethioate were found in the V9/A1 double-packaging model nr 1 as well as vacuum-packaged samples. On the other hand, those S-volatiles were not detected in the A1/V9 doublepackaging model nr 2. It seems that double-packaging model nr 2
is better than model nr 1 in removing S-volatiles because the proFCT218
566a
1562
0b
308bc
0b
304a
39
0
33
72ab
0b
0b
72
23
1053
34b
102a
0b
4168b
JOURNAL OF FOOD SCIENCE—Vol. 69, Nr. 3, 2004
duction of S-volatiles is critical in the middle of the irradiation process rather than storage. However, exposing double-packaged irradiated pork to aerobic conditions for 3 d was enough to eliminate
the sulfur compounds responsible for irradiation off-odor, regardless of packaging sequences.
Aerobic packaging was effective in eliminating S-volatiles but
increased lipid oxidation in pork loins (Table 1). Therefore, doublepackaging treatments such as exposing the irradiated meat to aerobic conditions for 1 to 3 d and then keep them in vacuum condiURLs and E-mail addresses are active links at www.ift.org
Prevention of pinking . . .
Off-odor b
Irradiation odor
Rancid odor
Nonirradiated
Vacuum Aerobic
1.0d
1.4
Table 9—Sensory characteristics of irradiated raw pork loin
with different packaging conditions (double-packaging
model nr 2) at day 10
Irradiated
V7/A3c
Vacuum
SEM
9.5b
3.9
11.3a
3.6
0.6
1.4
3.8c
4.8
Off-odor b
Irradiation odor
Rancid odor
Nonirradiated
Vacuum Aerobic
1.3c
3.6
4.4b
5.5
Irradiated a
A3/V7c Vacuum
5.6b
2.7
12.4a
2.8
SEM
1.0
1.2
a Means with different letters within a row are significantly different ( P < 0.05),
a Means with different letters within a row are significantly different ( P < 0.05),
n = 12. SEM = standard error of the means.
b 0.0: not detectable, 15.0: highly intense.
c Vacuum-packaged for 7 d then aerobically packaged for 3 d.
n = 12. SEM = standard error of the means.
b 0.0: not detectable, 15.0: highly intense.
c Aerobically packaged for 3 d then vacuum-packaged for 7 d.
tions for the remaining period should be used to control both irradiation off-odor and lipid oxidation in irradiated pork loins.
um bags a few days before use) in reducing off-odor volatiles, their
differences were relatively small.
Sensory characteristics
Pork loins from double-packaging model nr 1 (V7/A3) and nr 2
(A3/V7) were selected, and the sensory characteristics were compared with those from aerobic and vacuum-packaged ones (Tables
8 and 9). Most panelists easily distinguished the characteristic irradiation odor. The intensity of irradiation odor in irradiated vacuum-packaged pork was ranked the highest, double-packaged loins
in the middle, and aerobically packaged the lowest. The result of
the irradiation odor intensity was very consistent with the amount
of S-volatiles detected in the pork at 10 d (Table 6 and 7), showing
that S-volatiles are representative compounds responsible for the
irradiation odor. Hashim and others (1995) reported that irradiating raw chicken breast and thigh produced a characteristic “bloody
and sweet” aroma that remained after the thighs were cooked, but
was not detectable after the breasts were cooked. Ahn and others
(2000b) described the irradiation odor in raw pork as a “barbecued
corn-like” odor. Nam and others (2002) reported that during the
training sessions, panelists came to a consensus to describe the
irradiation odor from pork as sulfury, boiled sweet corn, or steamed
or rotten vegetables. On the other hand, panelists could not recognize rancid odor because the degree of lipid oxidation of irradiated
raw pork was not high enough to produce detectable rancid odor
and was masked by the strong irradiation odor.
Conclusions
T
he double-packaging method (exposing the irradiated pork to
aerobic conditions for a few days and then keeping the pork in
vacuum conditions for the remaining storage) was better than vacuum or aerobic packaging in controlling lipid oxidation and irradiation off-odor in pork loin. Although double-packaging model nr 2
(irradiating meat under aerobic packaging conditions and then
storing it under vacuum-packaging conditions a few days later) was
better than double-packaging model nr 1 (irradiating meat under
vacuum-packaging conditions and then removing the outer vacu-
URLs and E-mail addresses are active links at www.ift.org
Acknowledgments
This work was supported by the Natl. Pork Board. The NASA
FTCSC funded the purchase of the Solartek 72 Multimatrix-Vial
Autosampler used for the volatile analysis in this study.
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Vol. 69, Nr. 3, 2004—JOURNAL OF FOOD SCIENCE
FCT219
Food Chemistry and Toxicology
Table 8—Sensory characteristics of irradiated raw pork loin
with different packaging conditions (double-packaging
model nr 1) at day 10 a