Innovative Food Science & Emerging Technologies 3 Ž2002. 73᎐79
Effect of ionizing radiation on quality characteristics of
vacuum-packaged normal, pale᎐soft᎐exudative, and
dark᎐firm᎐dry pork 夽
K.C. Nam, M. Du, C. Jo, D.U. AhnU
Animal Science Department, Iowa State Uni¨ ersity, Ames, IA 50011-3150, USA
Accepted 2 November 2001
Abstract
Normal, pale᎐soft᎐exudative ŽPSE., and dark᎐firm᎐dry ŽDFD. pork Longissimus dorsi muscles were vacuum-packaged,
irradiated at 0, 2.5 or 4.5 kGy, and stored at 4 ⬚C for 10 days. The pH, color and lipid oxidation of pork were determined at 0, 5
and 10 days of storage. Volatile production from pork loins was determined at Day 0 and Day 10, and sensory characteristics at
Day 7 of storage. Irradiation increased the redness of vacuum-packaged normal, PSE and DFD pork. However, the 2-thiobarbituric acid reactive substances ŽTBARS. values of three types of pork were not influenced by irradiation and storage time.
Irradiation increased the production of sulfur ŽS.-containing volatile compounds, such as mercaptomethane, dimethyl sulfide,
carbon disulfide, methyl thioacetate, and dimethyl disulfide, as well as total volatiles in all three types of pork. Normal pork
produced higher levels of total and S-containing volatile compounds than the PSE and DFD pork did. The volatiles produced by
irradiation were retained in the vacuum packaging bag during storage. Although the odor preference for the three meat types of
pork was not different, the panelists could distinguish irradiated meat from the non-irradiated. Industrial rele¨ ance: Several US
meat companies have already started test-marketing irradiated meat products. Irradiation and the subsequent storage of pork
improved the color of PSE and DFD pork, and showed generally similar effects on the production of volatiles, except that there
appeared to be a lower level of S-volatiles in the PSE than in the other two samples. This indicated that irradiation can increase
the utilization of low-quality pork ŽPSE and DFD.. DFD pork, in particular, which has shorter shelf-life than the others, could
benefit the most from irradiation because the shelf-life of DFD meat can be extended significantly by both the methods of
vacuum packaging and irradiation. 䊚 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Irradiation; Vacuum packaging; pH of pork; Color; Volatiles; Sensory characteristics
Industrial rele¨ ance: Meat quality related to chemical aspects can be significantly influenced by irradiation. This study aimed to determine and
compare the effects of irradiation on lipid oxidation, off-flavor, color and sensory characteristics of vacuum packaged normal, pale-soft-exudative
ŽPSE. and dark-firm-dry ŽDFD. pork. Overall, irradiation increased redness, off-odor intensity and S-containing volatiles. Vacuum packaging
irradiated PSE and DFD were not different from normal pork in lipid oxidation, volatile production and sensory preference. Consequently
vacuum packaging and irradiation may offer an interesting combination process especially for DFD pork.
夽
Journal Paper No. J-18874 of the Iowa Agriculture and Home Economics Experiment Station, Ames, IA 50011. Project No. 3322, supported
by the Food Safety Consortium.
U
Corresponding author. Tel.: q1-515-294-6595; fax: q1-515-294-9143.
E-mail address: duahn@iastate.edu ŽD.U. Ahn..
1466-8564r02r$ - see front matter 䊚 2002 Elsevier Science Ltd. All rights reserved.
PII: S 1 4 6 6 - 8 5 6 4 Ž 0 1 . 0 0 0 5 8 - 3
74
K.C. Nam et al. r Inno¨ ati¨ e Food Science & Emerging Technologies 3 (2002) 73᎐79
1. Introduction
Irradiation can provide consumers with meat with
reduced risks from pathogens and parasites. Radiolytic
products are neither unique nor toxicologically significant in terms of the quantities found in irradiated meat
ŽSwallow, 1991; Thayer, 1994.. Fox et al. Ž1989. reported that vitamin losses from irradiated chicken at
doses up to 3 kGy and from pork at up to 1 kGy were
not nutritionally significant. Meat quality related to
chemical aspects, however, can be significantly influenced by irradiation. Murano Ž1995. reported that
radiolysis of myoglobin and lipids by irradiation could
lead to discoloration and rancidity or other off-odor
production. Apart from microbial spoilage, lipid oxidation is the primary process by which quality loss of
muscle food occurs ŽBuckley, Morrissey & Gray, 1995..
Initiators of lipid oxidation in irradiated meat are
hydroxyl radicals generated by the interaction of ionizing energy with water molecules in muscle tissues or in
meat products ŽThakur & Singh, 1994.. Regardless of
packaging type, irradiated raw pork patties produced
more volatiles than non-irradiated ones and developed
a characteristic aroma immediately after irradiation
ŽAhn, Olson, Jo, Chen, Wu & Lee, 1998.. The odor of
irradiated meat was also characterized as a barbecued
corn-like odor ŽAhn, Jo & Olson, 2000a.. Lebepe,
Molins, Charoen, Iv and Showronski Ž1990. reported
that irradiated vacuum-packaged pork had a fairly
stable bright red or pink color. The degree of color
changes by irradiation can vary depending on animal
species, muscle types and locations in a muscle, but are
commonly related to the oxygen availability of meat at
the time of irradiation and during storage. Vacuum
packaging Žor controlled atmosphere packaging. of
meat is a very satisfactory measure in preventing color
and rancidity problems in raw meat during storage
ŽRanken, 1987..
The ultimate pH of meat is also known to be a
crucial factor of meat quality. Depending on the ultimate pH and color of meat, pork can be classified as
normal, pale᎐soft᎐exudative ŽPSE., or dark᎐firm᎐dry
ŽDFD.. The distribution and proportion of free and
bound water in normal, PSE and DFD pork are different, and their biological membrane function should be
different as important barriers to deteriorative changes
that can affect meat quality ŽStanley, 1991.. PSE pork
could be more susceptible to oxidative changes and
could produce more off-flavor volatiles than normal or
DFD meat upon irradiation because of its denatured
muscle membrane structure. Chen and Waimaleongora-Ek Ž1981. concluded that the lower the pH values
in the raw chicken meat samples, the higher the TBARS
values. Ahn, Jo, Du, Olson and Nam Ž2000b. reported
that vacuum packaging was better than aerobic packaging for irradiation and subsequent storage of meat
because it minimized oxidative changes in pork during
storage.
The objective of this study was to determine and
compare the effects of irradiation on lipid oxidation,
off-flavor, color, and sensory characteristics of
vacuum-packaged normal, PSE, and DFD pork. The
results of this study could provide information on irradiation effects related to the pH of the meat, and could
be useful to treat efficiently each different grade of
pork for irradiation.
2. Materials and methods
2.1. Sample preparation and irradiation
Twnety-four pork loin Ž Longissimus dorsi . muscles,
which consisted of each of eight normal ŽpH 5.7᎐5.8.,
PSE ŽpH 5.4 or less. and DFD ŽpH 6.2᎐6.8. meat Žeight
replications., were purchased from a local packing
plant. The pork loins were trimmed of all surface fat,
and the lean muscle was sliced into 3-cm-thick steaks
and vacuum-packaged in nylonrpolyethylene bags Ž9.3
ml O 2rm2r24 h at 0 ⬚C: Koch, Kansas City, MO,
USA.. After packaging, they were stored overnight at 4
⬚C and then were irradiated at 0, 2.5 or 4.5 kGy using a
Linear Accelerator ŽCirce IIIR, Thomson CSF Linac,
Saint-Aubin, France.. The energy, beam power and
conveyor speed were 10 MeV, 10 kW and 38.7 mrmin,
respectively. The average dose rate was 92.0 kGyrmin
and the maxrmin ratio was approximately 1.12 for 2.5
kGy and 1.15 for 4.5 kGy. To confirm the target dose,
two alanine dosimeters per cart were attached to the
top and bottom surfaces of the sample. The alanine
dosimeter was read using a 104 Electron Paramagnetic
Resonance instrument ŽEMS-104, Bruker Instruments
Inc., Billerica, MA, USA.. Then, the pork steaks were
stored at 4 ⬚C for up to 10 days. The pH of the meat
samples was measured after 0, 5 and 10 days storage
after homogenizing samples with nine volumes of
deionized distilled water ŽDDW.. Color and lipid oxidation in vacuum-packaged irradiated pork loins was determined at 0, 5 and 10 days, volatile production at 0
and 10 days, and sensory characteristics at 7 days of
storage.
2.2. Color measurement
Color measurements were conducted on the packaged surface of samples with a Labscan spectrophotometer ŽHunter Associated Labs Inc., Reston, VA,
USA. that had been calibrated against white and black
reference tiles packaged in the same bags as those used
for meat packaging. Hunter L- Žlightness ., a- Žredness.,
and b- Žyellowness. values were obtained ŽAmerican
Meat Science Association, 1991. using a setting of D65
Ždaylight, 65-degree light angle.. An average value from
K.C. Nam et al. r Inno¨ ati¨ e Food Science & Emerging Technologies 3 (2002) 73᎐79
two random locations on each sample surface was used
for statistical analysis.
2.3. TBARS analysis
The fluorometric 2-thiobarbituric reactive substances
ŽTBARS. method ŽJo & Ahn, 1998. was used to determine lipid oxidation in raw meat. A minced sample
was weighed Ž3 g. into a test tube Ž50 ml., 9 ml of
deionized distilled water ŽDDW. was added, and the
mixture was homogenized with a Brinkman polytron
ŽType PT 10r35, Brinkman Instrument Inc., Westbury,
NY, USA. for 15 s at high speed. The meat homogenate Ž0.5 ml., sodium dodecylsulfate Ž8.1%, 200 ␮l.,
hydrochloric acid Ž0.5 M, 1.5 ml., thiobarbituric acid
Ž20 mM, 1.5 ml., butylated hydroxytoluene Ž7.2%, 50
␮l., and DDW Ž250 ␮l. were added to a test tube. The
sample was vortexed and heated in a 90 ⬚C water bath
for 15 min. After cooling for 10 min in cold water, 1 ml
of DDW and 5 ml of n-butanolrpyridine solution
Ž15:1, vrv. were added. The sample was vortexed and
centrifuged at 3000 = g for 15 min, and the resulting
upper layer was read by a fluorometer ŽModel 450,
BarnsteadrThermolyne, Dubuque, IA, USA. with 520
nm excitation and 550 nm emission. The amounts of
TBARS were expressed as milligrams of malondialdehyde ŽMDA.rkg meat.
2.4. Volatile compound analysis
A purge-and-trap apparatus ŽPrecept II and purgeand-trap 3000, Tekmar-Dohrmann, Cincinnati, OH,
USA. connected to a gas chromatographrmass spectrometer ŽGCrMS, Hewlett-Packard Co.. was used to
analyze the volatiles responsible for the off-odor in
samples. Two grams of the minced meat sample and
one pack of oxygen absorber ŽAgeless type Z-100, Mitsubishi Gas Chemical America, Inc., New York, NY,
USA. were placed in a 40-ml sample vial, and then the
vial was flushed with helium gas Ž99.999%. for 5 s. The
maximum holding time in a refrigerated Ž4 ⬚C. sample
tray before analysis was less than 10 h to minimize
oxidation during the holding time. The meat sample
was purged with helium gas Ž40 mlrmin. for min.
Volatiles were trapped at 30 ⬚C using a TenaxrSilica
gelrCharcoal column ŽTekmar-Dohrmann., desorbed
for 2 min at 220 ⬚C, focused in a cryofocusing unit at
y100 ⬚C, and then thermally desorbed into a column
for 30 s at 220 ⬚C. A combined column ᎏ an 8-m
HP-624 column Ž6% cyanopropyl phenyl q 94%
dimethyl siloxane co-polymer, 250 ␮m i.d. with 1.4 ␮m
nominal. and a 44-m HP-1 column Žpolydimethyl siloxane, 250 ␮m i.d. with 0.25 ␮m nominal. combined
using a zero dead-volume column connector ᎏ was
used for volatile analysis. Ramped oven temperature
was used Ž0 ⬚C for 2.5 min, increased to 10 ⬚C @ 2.5
⬚Crmin, to 80 ⬚C @ 10 ⬚Crmin, to 150 ⬚C @ 20
75
⬚Crmin, to 180 ⬚C @ 10 ⬚Crmin, and held for 1 min..
Inlet temperature was 180 ⬚C. Liquid nitrogen was used
to cool the oven to below ambient temperature. Helium was the carrier gas at a constant pressure of 20
psi. The ionization potential of MS was 70 eV and the
scan range was 33.1᎐300 mrz.
Identification of volatiles was achieved by comparing
mass spectral data of samples with those of the Wiley
Library ŽHewlett-Packard Co.. and standards when
available. The area of each peak was integrated using
ChemStation software ŽHewlett Packard Co.., and the
total peak area ŽpAU s. = 10 4 was reported as an indicator of volatiles generated from the meat samples. The
peaks produced by mass spectral data were grouped
into five major volatile classes ᎏ alcohols, ketones,
aldehydes, sulfur ŽS.-containing compounds and hydrocarbons ᎏ and reported.
2.5. Sensory analysis
The intensity and preference of odor of samples by
irradiation dose within a same pork type were determined at 7 days of storage by 76 sensory panelists.
Panelists also compared the odor characteristics of the
meat among three meat types within a same irradiation
dose. Training sessions were conducted to familiarize
panelists with the irradiation odor, the scale to be used,
and with the range of attribute intensities likely to be
encountered during the study. For the evaluation of
odor, samples containing 3 g of muscle in coded, capped
glass scintillation vials were presented to each panelist
in isolated booths. A 15-cm linear hedonic scale anchored with the words ‘no irradiation odor’ and ‘very
strong irradiation odor’ and ‘not preferable’ and ‘highly
preferable’ at opposite ends, were used to rate the
samples on the intensity of irradiation odor and preference of irradiation odor. The responses from the panelists were expressed in numerical values ranging from
0 Žno irradiation odor or not preferable. to 15 Žstrong
irradiation odor or highly preferable. to the nearest 0.1
cm.
2.6. Statistical analysis
The experimental design was to determine the effects of different meat type, irradiator storage time on
lipid oxidation, volatiles content, and color changes in
samples during a 10-day storage period. Data were
analyzed using SAS software ŽSAS Institute, Inc., 1990.
by a generalized linear model procedure, and the Student᎐Newman᎐Keuls multiple range test was used to
compare differences among means. Mean values and
standard errors of the means ŽS.E.M.. were reported.
Significance was defined at P- 0.05.
K.C. Nam et al. r Inno¨ ati¨ e Food Science & Emerging Technologies 3 (2002) 73᎐79
76
Table 1
The pH of vacuum-packaged normal, PSE and DFD pork Longissimus dorsi muscle affected by irradiation dose and storage time at 4 ⬚C
Storage time
Day 0
Day 5
Day 10
UU
S.E.M.
0 kGy
2.5 kGy
4.5 kGy
U
Norm
PSE
DFD
Norm
PSE
DFD
Norm
PSE
DFD
S.E.M.
5.76b
5.62bc
5.62b
0.08
5.42c
5.47bc
5.37c
0.02
6.36a
6.36a
6.36a
0.07
5.66bc
5.61bc
5.58b
0.04
5.43c
5.42c
5.33c
0.03
6.35a
6.47a
6.40a
0.06
5.66bc
5.63b
5.58b
0.04
5.47c
5.49bc
5.33c
0.03
6.43a
6.38a
6.40a
0.07
0.06
0.05
0.05
a᎐c
Means with different letters within a row are different Ž P - 0.05.. Abbre¨ iations: PSE, pale᎐soft᎐exudative; DFD, dark᎐firm᎐dry.
S.E.M.: standard error of the means among meats within a storage time.
UU
S.E.M.: standard error of the means within a meat type.
U
3. Results and discussion
10 days of storage.. The exact reason for this phenomenon is not known, but the residual oxygen in the
vacuum packaging bag could have oxidized myoglobin
at the early part of the storage time. Meat type and
irradiation did not affect b-values. Irradiated PSE and
DFD samples at 4.5 kGy showed an increasing trend in
b-values during storage, but yellowness has little effect
on the overall color of meat.
3.1. Effect of irradiation on pH and color
The pH values of non-irradiated and irradiated normal, PSE and DFD pork ŽTable 1. showed that irradiation had no effect on the pH of all three pork types.
The original ultimate pH of normal, PSE and DFD
meat was also maintained during the 10-day storage
period.
Irradiated, vacuum-packaged pork loins had Ž P0.05. greater a-values than the non-irradiated samples,
and the increase of a-values in pork loins was irradiation dose-dependent in all three pork types ŽTable 2..
Earlier findings also showed that irradiation increased
the redness of pork in vacuum packaging ŽLuchsinger
et al., 1996; Nanke, Sebranek & Olson, 1998.. The
a-value in three types of pork with vacuum packaging
decreased after 5 days of storage, but increased after
3.2. Effect of irradiation on TBARS ¨ alue
The overall TBARS values of vacuum-packaged pork
loins were trivial levels regardless of meat type, irradiation, and storage time ŽTable 3.. At Day 0 and Day 10,
DFD pork had lower TBARS values than the normal
or PSE pork. DFD pork was stable and resistant to
both irradiation- and storage-dependent quality
changes. Although DFD meat is more susceptible to
bacterial spoilage than the other pork types, irradiation
Table 2
Color L- a- and b-values of vacuum-packaged normal, PSE and DFD pork Longissimus dorsi muscle affected by irradiation dose and storage time
at 4 ⬚C
Norm
PSE
DFD
Norm
PSE
DFD
Norm
PSE
DFD
L-¨ alue
Day 0
Day 5
Day 10
S.E.M.
50.5b
49.9bc
54.2ab c
1.3
59.6ax
52.3abz
55.8aby
1.1
43.4d
43.1d
47.2de
1.6
52.0bx
48.8cy
52.4bcx
1.0
60.6ax
54.7ay
56.9aby
0.9
47.2cx
42.8dy
49.5cdx
1.5
52.4b
48.4c
56.6ab
1.3
57.2a
54.6a
59.5a
1.4
43.0dxy
40.9dy
46.0ex
1.1
1.1
0.9
1.6
a-¨ alue
Day 0
Day 5
Day 10
S.E.M.
5.8cx
2.6dz
4.4cy
0.4
3.7dy
2.9dy
5.2cx
0.5
6.8cx
3.6dy
6.2cx
0.6
9.8bx
7.1by
8.6bxy
0.6
9.7bx
7.3bz
8.7by
0.3
10.4bx
6.0cy
10.3abx
0.6
12.9ax
10.0ay
11.3axy
0.6
12.4ax
9.7ay
11.4ax
0.6
11.9ax
9.4ay
11.0abx
0.4
0.5
0.4
0.7
11.2y
9.8bcy
11.7x
0.3
12.5x
10.7aby
11.7xy
0.4
9.5
9.1cd
9.4
0.8
10.1xy
8.7dy
11.6
0.6
11.0
10.1ab
9.6
0.6
11.7y
10.8ab
12.1
0.8
9.5y
8.7dy
10.7x
0.3
0.3
0.3
0.8
b-¨ alue
Day 0
Day 5
Day 10
UU
S.E.M.
0 kGy
2.5 kGy
U
Storage
time
11.1
10.0ab
11.1
0.4
4.5 kGy
12.2
11.0a
12.6
0.2
S.E.M.
a᎐e
Means with different letters within a row are significantly different Ž P - 0.05.. x ᎐ z Means with different letters within a column are
significantly different Ž P- 0.05.. Abbre¨ iations: PSE, pale᎐soft᎐exudative; DFD, dark᎐firm᎐dry.
U
S.E.M.: standard error of the means among meats within a storage time.
UU
S.E.M.: standard error of the means within a meat type.
K.C. Nam et al. r Inno¨ ati¨ e Food Science & Emerging Technologies 3 (2002) 73᎐79
77
Table 3
TBARS values of vacuum-packaged normal, PSE and DFD pork Longissimus dorsi muscle affected by irradiation dose and storage time at 4 ⬚C
Storage
time
Day 0
Day 5
Day 10
UU
S.E.M.
0 kGy
Norm
2.5 kGy
PSE
DFD
TBARS Žmg MDArkg meat.
0.09ab x
0.11ab
0.07b
y
0.07
0.08
0.06
0.10ab x
0.09bc
0.07d
0.04
0.03
0.01
U
4.5 kGy
S.E.M.
Norm
PSE
DFD
Norm
PSE
DFD
0.11abx
0.08xy
0.10abxy
0.06
0.15ax
0.09y
0.11aby
0.10
0.09ab
0.08
0.07d
0.01
0.12ab
0.10
0.14a
0.07
0.10ab
0.10
0.11ab
0.07
0.10ab
0.10
0.08d
0.01
0.01
0.04
0.09
a᎐d
Means with different letters within a row are significantly different Ž P- 0.05.. x ᎐ y Means with different letters within a column are
significantly different Ž P- 0.05.. Abbre¨ iations: PSE, pale᎐soft᎐exudative; DFD, dark᎐firm᎐dry.
U
S.E.M.: standard error of the means among meats within a storage time.
UU
S.E.M.: standard error of the means within a meat type.
with vacuum packaging could extend the shelf-life and
increase the utilization of even DFD pork. Our results
agree with those of Yasosky, Aberle, Peng, Mills and
Judge Ž1984., who reported that the ultimate pH of
ground pork was negatively correlated with the TBARS
values of pork after 12 days of storage at 2 ⬚C. Low pH
values in meat play an important role in lipid oxidation
by denaturing antioxidant proteins, disrupting cell
structure, and exposing membrane lipids to free radicals. The distribution of water and its location, where
hydroxyl radicals are formed by irradiation and storage,
could be critical for the irradiation-dependent reaction.
Therefore, it was expected that the denatured membrane structure of PSE pork would make it more
susceptible to lipid oxidation than normal and DFD
pork. However, irradiation and subsequent storage did
not increase lipid oxidation in three types of pork with
vacuum packaging because no oxygen was available for
hydroperoxide formation. The difference in TBARS
among the three types was caused only by the pH of
the pork.
3.3. Volatile compounds in irradiated pork
At Day 0, non-irradiated PSE pork loins produced
the highest amount of alcohols Ž98% of which was
ethanol., but produced the lowest amounts of ketones
and aldehydes among the three pork types ŽTable 4..
S-containing compounds in all three meat types increased with irradiation. The amount of S-containing
volatiles in irradiated normal pork was higher than that
of the PSE and DFD pork. The increase of irradiation
dose from 2.5 to 4.5 kGy had a minimal impact on the
production of most major volatile groups, except S-containing compounds of DFD pork. The major ketones
identified were 2-propanone and 2-butanone, and the
major aldehydes were acetaldehyde, 3-methyl butanal,
pentanal, and hexanal. Sulfur-containing volatile compounds were mercaptomethane, dimethyl sulfide, carbon disulfide, methyl thioacetate, and dimethyl disulfide, and they increased greatly Ž P- 0.01. after irradiation, regardless of meat types. Patterson and Stevenson
Ž1995. found that dimethyltrisulfide was the most potent off-odor compound, and that the changes that
occur following irradiation were distinctively different
from those of warmed-over flavor in oxidized meat.
Ahn et al. Ž2000b. reported that S-containing volatiles
such as dimethyl disulfide produced by the radiolysis of
amino acids were responsible for the off-odor in irradiated pork. They also assumed that the off-odor production in irradiated pork was caused by the compounding
effects of lipid oxidation products and radiolytic
products of amino acid side chains.
After 10 days of storage, the amounts of alcohols in
non-irradiated normal pork and ketones in non-irradiated PSE pork were the highest of all as of Day 0 ŽTable
4.. The amounts of S-containing volatiles in irradiated
pork increased after 10 days of storage, and were also
irradiation dose-dependent in all three pork types. PSE
pork produced the least amount of S-containing
volatiles after irradiation. Irradiated pork produced
more hydrocarbons than non-irradiated after 10 days of
storage. The amounts of total volatiles in both irradiated and non-irradiated normal pork were higher than
those of PSE and DFD pork.
3.4. Sensory characteristics of irradiated pork
Irradiation dose influenced Ž P- 0.05. the intensity
of irradiation odor and the acceptance of the meat
odor ŽTable 5.. Irradiation increased Ž P- 0.05. the
intensity of irradiation odor in all three pork types, but
there was no difference among meat type. The result of
the irradiation odor intensity was consistent with that
of S-containing volatiles produced ŽTable 4.. Therefore,
S-containing volatiles could be a representative irradiation odor detected by panelists.
The acceptance of the meat odor was adverse to the
irradiation odor intensity. As the irradiation odor intensity increased, the preference of meat odor decreased. Most trained panelists rated irradiation odor
as an off-odor. Hashim, Resurrecccion and MacWatters Ž1995. showed that irradiating uncooked chicken
breast and thigh produced a characteristic bloody and
78
Storage
time
0 kGy
Norm
2.5 kGy
PSE
4.5 kGy
DFD
Norm
PSE
DFD
Norm
S.E.M.
PSE
DFD
Peak area ŽpAU s. = 104
Day 0
Alcohols
Ketones
Aldehydes
S-compounds
Hydrocarbons
Total volatiles
2770b
11 501a
1309ab
134c
1511
17 613b
17 543a
286c
945bc
1155b
1720
22 571a
2959b
1838c
1691a
55c
1130
8047c
1121b
6742b
539c
3111a
2229
14 539b
553b
356c
565c
895b
1621
7314c
0b
97c
367c
1009b
1584
3274c
206b
1139c
390c
3361a
2611
8526c
458b
489c
771c
1128b
3363
6793c
0b
614c
508c
2814a
1542
5923c
724
1415
138
191
245
1868
Day 10
Alcohols
Ketones
Aldehydes
S-compounds
Hydrocarbons
Total volatiles
1957b
27 948a
328bc
211d
1302cd
32 654a
15 748a
432c
227bc
903d
1207de
19 167bc
82d
275c
149c
77d
914e
1590d
197d
2703c
265bc
6683a
3542a
14 247bc
1490b
1670c
301bc
1364c
1978c
7479cd
135d
670c
184c
4461b
1390cd
7530cd
633c
17 312b
533a
7631a
3161a
31 178a
1278b
1808c
417ab
2411b
2822b
9684c
154d
650c
152c
6298a
1766cd
9797c
286
1735
49
459
177
1824
a᎐f
Means with different letters within a row are significantly different Ž P- 0.05.. S.E.M.: standard error of the means among meats within a storage time. Abbre¨ iations: PSE,
pale᎐soft᎐exudative; DFD, dark᎐firm᎐dry.
K.C. Nam et al. r Inno¨ ati¨ e Food Science & Emerging Technologies 3 (2002) 73᎐79
Table 4
Relative production of volatiles in vacuum-packaged normal, PSE and DFD pork Longissimus dorsi muscle affected by irradiation dose at storage time at 4 ⬚C
K.C. Nam et al. r Inno¨ ati¨ e Food Science & Emerging Technologies 3 (2002) 73᎐79
Table 5
Sensory characteristics of vacuum-packaged irradiated normal, PSE
and DFD pork Longissimus dorsi muscle refrigerated for 7 days
Irradiation
UUU
Norm
PSE
DFD
S.E.M.
4.37ay
9.56ax
10.14ax
0.30
3.95aby
8.31bx
8.32bx
0.36
3.14bz
6.83cy
8.58bx
0.33
0.34
0.32
0.33
8.51x
5.72by
5.26y
0.38
8.75x
6.01by
5.89y
0.35
9.58x
7.23ay
6.34y
0.34
0.35
0.32
0.35
Uz
Irradiation odor intensity
0 kGy
2.5 kGy
4.5 kGy
S.E.M.
UU
Acceptance of meat odor
0 kGy
2.5 kGy
4.5 kGy
UUUU
S.E.M.
a᎐c
Means with different letters within a row are significantly
different Ž P- 0.05., n s 76. a ᎐ c Means with different letters within a
column are significantly different Ž P- 0.05., n s 76. Abbre¨ iations:
PSE, pale᎐soft᎐exudative; DFD, dark᎐firm᎐dry.
U
Irradiation odor intensity: 0, no irradiation odor; 15, very strong
irradiation odor.
UU
Acceptance of meat odor: 0, not preferable; 15, highly preferable.
UUU
S.E.M.: standard error of the means among meats within an
irradiation dose.
UUUU
S.E.M.: standard error of the means among irradiation dose
within a meat type.
sweet aroma that remained after the thighs were
cooked, but was not detectable after the breasts were
cooked. Panelists could easily distinguish odors of irradiated and non-irradiated meat, but not among the
three meat types.
4. Conclusion
Irradiation increased redness, off-odor intensity, and
S-containing volatiles regardless of the pH of vacuumpackaged pork. Irradiation of pork with vacuum packaging increased the red color even in PSE pork. With
vacuum packaging, irradiated PSE and DFD pork were
not different from the normal pork in lipid oxidation,
volatile production, and sensory preference. Therefore,
DFD pork, which is more susceptible to rapid bacterial
growth due to its high pH than the others, could
benefit the most from irradiation because the shelf-life
of DFD meat can be extended significantly by the
method of both vacuum packaging and irradiation.
Irradiation and vacuum-packaged storage of meat may
be desirable for long-term storage, but may reduce the
acceptance of irradiated meat due to its retained high
level of S-volatiles. Double packaging ᎏ individual
packaging of meat with oxygen permeable film and
repackaging multiple individual packages in large vacuum-packaging bags for irradiation and storage ᎏ and
opening the outside vacuum packaging bag 1᎐2 days
before sale, is recommended to reduce irradiation odor.
79
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