JFS:
Sensory and Nutritive Qualities of Food
Lipid Oxidation, Color, Volatiles, and Sensory
Characteristics of Aerobically Packaged and
Irradiated Pork with Different Ultimate pH
K.C. NAM, D.U. AHN, M. DU, AND C. JO
ABSTRACT: Irradiation and storage increased lipid oxidation of normal and pale-soft-exudative (PSE) muscles,
whereas dark-firm-dry (DFD) muscle was very stable and resistant to oxidative changes. Irradiation increased
redness regardless of pork-quality type, and the increases were proportional to irradiation dose. Irradiation increased the production of sulfur-containing volatiles, but not lipid oxidation products. The total volatiles produced
in normal and PSE pork were higher than the DFD pork. Some volatiles produced in meat by irradiation evaporated
during storage under aerobic packaging conditions. Nonirradiated normal and DFD pork had higher odor preference scores than the nonirradiated PSE, but irradiation reduced the preference scores of all 3 pork-quality types.
Key Words: irradiation, pork ultimate pH, color, lipid oxidation, volatiles
I
technology to control microorganisms and parasites and to extend shelf
life in raw meats. Nutritional disadvantages of irradiation have not been reported other than that thiamin is reduced in irradiated beef; more thiamin,
however, is lost when beef is cooked
than irradiated (Giroux and Lacroix
1999). Many researchers have reported
that irradiation induces oxidative chemical changes, the formation of off odor,
and color changes. Irradiation also increases 2-thiobarbituric acid (TBARS)
values in meats. Initiators of lipid oxidation in irradiated meat are considered
to be hydroxyl radicals generated by
the interaction of ionizing energy with
water molecules in muscle tissues or in
meat products (Thakur and Singh
1994). Regardless of packaging type, irradiated raw pork patties produced
more volatiles than nonirradiated ones
and developed a characteristic aroma
immediately after irradiation (Ahn and
others 1998). Hashim and others (1995)
showed
that
irradiating
uncooked
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. Millar and
others (1995) reported that the redness
of chicken breast increased after ionizing irradiation in oxygen-permeable
film. The changes in meat color after irradiation were highly dependent on animal species, muscle type, and location
in a muscle (Nanke and others 1998).
© 2001 Institute of Food Technologists
The impacts of irradiation on meat color could be related to oxygen availability and the amount of free radicals
formed at the time of irradiation.
The ultimate pH of meat is also
known to be a crucial factor for meat
quality. Pork, depending on the ultimate pH, can be classified as normal,
pale-soft-exudative (PSE), or darkfirm-dry (DFD); and each classification
has its own distinctive color, texture,
and flavor characteristics. The distribution and proportion of free and
bound water in normal, PSE, and DFD
pork are different. PSE pork upon irradiation would be more susceptible to
oxidative changes and produce more
off-flavor volatiles than irradiated normal or DFD meat due to its denatured
muscle structure. Chen and Waimaleongora-Ek (1981) reported that the
lower the pH value in the raw chicken
meat sample, the higher the TBARS
values. Silva and others (1999) showed
that DFD pork was more susceptible to
bacterial spoilage and was less flavorful than the normal pork. In addition,
the response of normal, PSE, and DFD
muscles to color changes upon irradiation could be different from each other. However, little work has been done
to determine the effect of irradiation
on the quality changes of raw pork
with different ultimate pH.
The objective of this study was to determine and compare the effects of irradiation on lipid oxidation, off-odor
volatiles, and color of aerobically packaged normal, PSE, and DFD pork during
refrigerated storage.
Materials and Methods
Sample preparation
Twenty-four pork loin (Longissimus
dorsi) muscles, 8 each of normal (pH
5.7 to 5.8), PSE (pH 5.4 or less) and
DFD (pH 6.2 to 6.8) meat, were purchased from a local packing plant. The
pork loins were trimmed of all fat from
the surface, and the lean muscle was
sliced to 3-cm thick steaks and packaged in polyethylene oxygen permeable bags. After packaging, they were
stored overnight at 4 ⬚C and then irradiated using a Linear Accelerator (Circe IIIR, Thomson CSF Linac, SaintAubin, France). The target doses of
irradiation were 0, 2.5, and 4.5 kGy.
The energy and power level used were
10 MeV and 10 kw, respectively, and
the average dose rate was 92.0 kGy/
min. The max/min ratio was approximately 1.12 for 2.5 kGy and 1.15 for 4.5
kGy. To confirm the target dose, 2 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 (Bruker Instruments Inc., Billerica, Mass., U.S.A.).
The pork steaks were stored at 4 ⬚C for
up to 10 d. The pH of meat samples
was measured after 0, 5, and 10 d of
storage after homogenizing samples
with 9 vol. of deionized distilled water
(DDW). Color and lipid oxidation in
aerobically packaged irradiated pork
loins were determined at 0, 5, and 10 d,
volatile production at 0 and 10 d, and
sensory analysis at 7 d of storage.
Vol. 66, No. 8, 2001—JOURNAL OF FOOD SCIENCE
1225
SensoryandNutritiveQualitiesofFood
Introduction
RRADIATION IS THE BEST AVAILABLE
Irradiation Impact on the Quality of Pork with Different Ultimate pH . . .
Table 1—The pH of aerobically packaged normal, PSE, and DFD pork
Longissumus dorsi muscle affected by irradiation dose and storage time at
4 ⬚C
Storage
0 kGy
2.5 kGy
4.5 kGy
time
Norm
PSE
DFD
Norm
PSE
DFD
Norm
PSE
Day 0
Day 5
Day 10
SEM2
5.69b
5.63b
5.64b
0.04
5.47c
5.46bc
5.45cd
0.04
6.39a
6.42a
6.53a
0.06
5.64b
5.60b
5.59bc
0.03
5.46c
5.40c
5.40d
0.03
6.35a
6.42a
6.47a
0.06
5.67b 5.50c
5.66b 5.46bc
5.58bc 5.49bcd
0.04
0.02
DFD SEM1
6.32a 0.04
6.30a 0.05
6.40a 0.04
0.05
a-dDifferent letters within a row are different (P ⬍ 0.05), n = 8.
1 SEM: Standard errors of the mean among different meat type x irradiation within a storage time.
2 SEM: Standard errors of the mean among different storage time within a meat type.
Color measurement
Color measurements were conducted on the surface of samples with a
LabScan
spectrophotometer
(Hunter
Associated Labs. Inc., Reston, Va.,
U.S.A.) that had been calibrated against
white and black reference tiles. Hunter
L- (lightness), a- (redness), and b- (yellowness) values were obtained (American Meat Science Assn. 1991) using a
setting of D65 (daylight, 65-degree light
angle). An average value from 2 random
locations on each sample surface was
used for statistical analysis.
TBARS value
SensoryandNutritiveQualitiesofFood
The fluorometric 2-thiobarbituric
reactive substances (TBARS) method
(Jo and Ahn 1998) was used to determine the extent of lipid oxidation in raw
meat. Minced sample (3 g) was weighed
and placed in a test tube (50 mL). Nine
mL of deionized distilled water (DDW)
was added, and the mixture homogenized with 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 (0.5 mL),
sodium dodecylsulfate (8.1% 200 ␮L),
hydrochloric acid (0.5 M, 1.5 mL),
thiobarbituric acid (20 mM, 1.5 mL),
butylated hydroxytoluene (7.2%, 50 ␮L),
and DDW (250 ␮L) were added in 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-butanol/pyridine solution (15:1, v/v) were added.
The sample was vortexed and centrifuged 3000 ⫻ g for 15 min, and the resulting upper layer was read by a fluorometer
(Model
450,
Barnstead/
Thermolyne, Dubuque, Iowa, U.S.A.)
with 520 nm excitation and 550 nm
emission. The amounts of TBARS were
expressed as milligrams of malondialdehyde per kilogram of meat.
Volatiles compound analysis
A
1226
purge-and-trap
apparatus
(Pre-
cept II and purge-and-trap 3000, Tekmar-Dohrmann) connected to a gas
chromatograph/mass
spectrometry
(GC/MS, Hewlett-Packard) was used to
analyze the volatiles responsible for the
off odor in samples. Two-g of minced
sample and 1 pack of oxygen absorber
(Ageless type Z-100, Mitsubishi Gas
Chemical America Inc., New York, N.Y.,
U.S.A.) were placed in a 40-mL sample
vial. The vials were then flushed with
helium gas (99.999%) for 5 s. The maximum holding time in a refrigerated
(4 ⬚C) sample tray before analysis was
less than 10 h to minimize the oxidation
during the holding time. The meat sample was purged with helium gas (40 mL/
min) for 11 min. Volatiles were trapped
at 30 ⬚C using a Tenax/Silica gel/Charcoal column (Tekmar-Dohrmann) and
desorbed for 2 min at 220 ⬚C, focused in
a cryofocusing unit at –100 ⬚C, and then
thermally desorbed into a column for
30 s at 220 ⬚C. A combined column—an
HP-624 (8 m, 250 ␮m i.d., 1.4 ␮m nominal) column with an HP-1 column (44
m, 250 ␮m i.d., 0.25 ␮m nominal) using
a zero dead-volume column connector—was used for volatile analysis.
Ramped oven temperature was used
(0 ⬚C for 2.5 min, increased to 10 ⬚C at
2.5 ⬚C/min, increased to 80 ⬚C at 10 ⬚C/
min, increased to 150 ⬚C at 20 ⬚C/min,
increased to 180 ⬚C at 10 ⬚C/min, and
held for 1 min). Inlet temperature was
180 ⬚C. Liquid nitrogen was used to cool
the oven below ambient temperature.
Helium was the carrier gas at a constant pressure of 20.5 psi. The ionization potential of MS was 70 eV, and the
scan range was 18.1 to 300 m/z.
Identification
of
volatiles
was
achieved by comparing mass spectral
data of samples with those of the Wiley
library (Hewlett-Packard) and standards, when available. The area of each
peak was integrated using ChemStationTM software (Hewlett Packard), and
the total peak area (pA*sec) ⫻ 10 4 was
reported as an indicator of volatiles
JOURNAL OF FOOD SCIENCE—Vol. 66, No. 8, 2001
generated from the meat samples. The
peaks produced by mass spectral data
were grouped into 5 major volatile
classes—ketones, alcohols, aldehydes,
sulfur (S)-containing compounds, and
hydrocarbons—and reported.
Sensory analysis
The intensity of off odor and preference for the odor of meat samples were
determined at 7 d of storage using 76
sensory panelists. For evaluation of
odor, samples containing 3-g muscle in
coded, capped glass scintillation vials
were presented to each panelist in isolated booths. A 15-cm linear hedonic
scale, anchored at opposite ends with
the words “no off odor” and “very
strong odor,” and “not preferable” and
“highly preferable,” was used to rate the
samples on the intensity of irradiation
odor and on the preference for the irradiation odor. The responses from the
panelists were expressed in numerical
values ranging from 0 (no off odor or
not preferable) to 15 (very strong odor
or highly preferable) to the nearest 0.1
cm.
Statistical analysis
The experimental design was to determine the effects of different meat
type, irradiation, and storage time on
lipid oxidation, volatiles content, and
color changes in samples during the 10d storage. Data were analyzed using
SAS software (SAS Institute Inc. 1985)
by the generalized linear model procedure; the Student-Newman-Keul’s multiple range test was used to compare
differences among means. Mean values
and standard error of the means (SEM)
were reported. Significance was defined
at P ⬍ 0.05.
Results and Discussion
pH
The pH values for the nonirradiated
and irradiated normal, PSE, and DFD
pork (Table 1) showed that irradiation
had no effect on the pH of all 3 quality
types of pork Longissimus dorsi muscle
with aerobic packaging. The original ultimate pH of normal, PSE, and DFD
meat has been maintained throughout
the 10-d storage.
Color
The lightness, redness, and yellowness of 3 different grades of pork loins
with aerobic packaging were compared
by irradiation dose and storage time
(Table 2). The most important factor influencing L-values was meat type (P
Irradiation Impact on the Quality of Pork with Different Ultimate pH . . .
Storage
time
L-value
Day 0
Day 5
Day 10
SEM2
a-value
Day 0
Day 5
Day 10
SEM2
b-value
Day 0
Day 5
Day 10
SEM2
0 kGy
Norm
PSE
48.1by
51.3bcx
48.9cy
0.8
2.5 kGy
4.5 kGy
DFD SEM1
DFD
Norm
PSE
DFD
Norm
PSE
54.9a
53.5ab
51.9bc
0.9
42.3c
41.9d
44.8d
1.1
49.5b
52.1b
51.7bc
1.0
56.7a
55.9bc
58.1a
1.0
37.0dy
43.1ax
44.6dx
1.4
47.5b
49.5c
50.2bc
1.0
54.9a
52.8abc
53.1b
1.0
42.2c
42.2d
42.1d
0.9
7.1dey
9.1ay
9.8abcx
0.4
6.6ey
7.8abcxy
9.1bcx
0.5
7.0dey
5.6dy
9.1bcx
0.5
8.6cdy
7.9abcy
10.3abx
0.3
8.9cdx
6.5cdz
7.8cy
0.2
10.5bcx
7.0bcy
12.0ax
0.7
13.2ax
8.9az
11.1aby
0.6
11.9abx
7.3bcz
9.5bcy
0.5
12.5ax 0.5
8.5aby 0.4
11.8ax 0.6
0.7
11.0by
13.2abx
13.6abx
0.2
12.7az
13.8ay
14.6ax
0.2
9.5cdy 10.9bz
9.8cy 13.4aby
11.8cx 14.4ax
0.5
0.2
12.7ay
14.1ax
14.9ax
0.3
8.6dy
10.0cy
12.6bcx
0.5
11.0bz
12.5by
14.4ax
0.3
12.6az
13.6aby
14.6ax
0.3
10.2bcy 0.4
9.8cy 0.3
11.7cx 0.4
0.3
1.1
0.9
1.1
a-e Different letters within a row are significantly different ( P ⬍ 0.05), n = 8.
x-z Different letters within a column of same color value are significantly different (P ⬍ 0.05).
1 SEM: Standard errors of the mean among different meat type x irradiation within a storage time.
2 SEM: Standard errors of the mean among different storage time within a meat type.
Table 3—TBARS values of aerobically packaged normal, PSE, and DFD pork
Longissumus dorsi muscle affected by irradiation dose and storage time at
4 ⬚C
Storage
0 kGy
2.5 kGy
4.5 kGy
time
Norm
PSE
DFD
Norm
PSE
DFD
Day 0
Day 5
Day 10
SEM2
0.10cy
0.10cy
0.10c
0.10cy
0.12aby
0.10c
0.24bx
0.25bx
0.04
0.20bxy 0.09c
0.23bx 0.09b
0.03
0.01
0.32ax 0.26aby
0.35abx 0.64ax
0.06
0.10
0.11c
0.11b
0.01
Norm
0.13ay
PSE
DFD SEM1
0.13aby
0.10cy 0.01
0.28abxy 0.28abxy 0.12cx 0.04
0.38abx 0.47abx 0.12bx 0.09
0.07
0.07
0.01
a-c Different letters within a row are significantly different ( P ⬍ 0.05), n = 8.
x-y Different letters within a column are significantly different ( P ⬍ 0.05).
1 SEM: Standard errors of the mean among different meat type x irradiation within a storage time.
2 SEM: Standard errors of the mean among different storage time within a meat type.
0.01). PSE pork, which has low pH, had
the highest L-value, whereas DFD pork
had the lowest L-value among the 3
meat types. Irradiated pork loin had
(P ⬍ 0.01) greater a-values than nonirradiated pork chops regardless of meat
type, and the increase in a-values was
proportional to irradiation dose. Furthermore, the redness was not decreased during the 10-d storage period
even in aerobic packaging conditions.
Although there have been several inconsistent results (Satterlee and others
1971; Luchsinger and others 1996) in
terms of the stability of increased redness in irradiated meat, the red/pink
pigment formed by irradiation in this
experiment was not easily oxidized.
Therefore, irradiation could have a desirable effect on improving the color of
PSE pork, which has a detrimental pale
color and reduced pigment stability
(Livingston and Brown 1981; Sorheim
and others 1997). The b-values of PSE
loin meats were higher (P ⬍ 0.01) than
the normal and DFD samples at 0 d of
storage. Color b-value increased during
storage in all 3 pork types, but yellowness usually does not have much impact on the overall color of meat. Irradiation had no effect on the b-values of
pork loin.
TBARS values
Meat type, irradiation, and storage
time all influenced lipid oxidation of
aerobic-packaged pork loin (Table 3).
Irradiation and storage time increased
(P ⬍ 0.01) the TBARS values of normal
and PSE loin muscles, whereas DFD
loin was not influenced by irradiation.
DFD loin was very stable and resistant
to the quality changes by irradiation
and storage. DFD meat has high water
holding capacity and intact membrane
structure, which can act as a barrier
against the attack of free radicals, such
as hydroxyl radicals. Therefore, irradiation could be more useful for DFD
meat than for the normal and PSE
meats. Because DFD meat is more susceptible to bacterial spoilage than other
pork types, its use as a meat ingredient
or for retail cuts is highly limited. However, if combined with irradiation, DFD
meat could be an excellent meat source
for further processing or for retail cuts.
PSE pork was more susceptible to
lipid oxidation than the normal and
DFD porks when irradiated and stored
under aerobic conditions (Table 3). Our
result agreed with Yasosky and others
(1984) who reported that the ultimate
pH of ground pork was negatively correlated with the TBARS values after 12 d
of storage at 2 ⬚C. Cooked meat is highly susceptible to lipid oxidation because
the cooking process denatures antioxidant components, damages cell structure, and exposes membrane lipids to
the environment (Ahn and others 1998).
The antioxidant effect was more notable when the irradiated raw turkey patties were loosely packaged than when
they were vacuum-packaged (Ahn and
others 1997). As in cooked meat, the
membrane structure of PSE pork would
be leaky because of protein denaturation by low pH and high carcass temperature at early postmortem. Through
the holes generated by denatured
membrane proteins, water molecules
can easily get into membrane bilayers.
Along with the water, free ionic iron
and iron proteins confined inside of
cells under normal conditions may also
get into membrane bilayers and promote oxidative reactions when free radicals are available. Hydroxyl radicals
can be formed from water molecules in
all meat conditions upon irradiation,
and the reaction of hydroxyl radicals is
site specific because of their short halflife (10 –6 s). Therefore, the distribution
of water and its location are critical for
the irradiation-dependent initiation of
lipid oxidation. Also, the susceptibility
of muscle tissues to lipid oxidation is
closely related to the nature, proportion, degrees of unsaturation of the fatty acids in the lipids, and the composition of phospholipids in the cell
membrane (Gray and others 1996).
Volatile compounds
Meat type as well as storage time affected (P ⬍ 0.05) the production and
the composition of volatiles in aerobically packaged pork loins (Table 4). At d
0 of storage, nonirradiated normal pork
loins produced the higher amount of
ketones than the PSE and DFD porks,
but PSE pork produced the higher
amount of alcohols and total volatiles
than the normal and DFD porks. The
Vol. 66, No. 8, 2001—JOURNAL OF FOOD SCIENCE
1227
SensoryandNutritiveQualitiesofFood
Table 2—Color L-, a-, and b-values of aerobically packaged normal, PSE, and
DFD pork Longissumus dorsi muscle affected by irradiation dose and storage
time at 4 ⬚C
Irradiation Impact on the Quality of Pork with Different Ultimate pH . . .
Table 4—Relative production of volatiles in aerobically packaged normal, PSE,
and DFD pork Longissumus dorsi muscle affected by irradiation dose at different storage times at 4 ⬚C
also influenced by irradiation, but their
changes by irradiation were not as severe as those of other volatile groups.
Storage
0 kGy
2.5 kGy
4.5 kGy
As storage time increased, the comtime
Norm PSE
DFD Norm PSE
DFD
Norm PSE
DFD SEM1 position of volatiles in pork changed
significantly. Large amounts of ketones
Peak area (pA*sec) ⫻ 104
from nonirradiated normal and alcoDay 0
hols from nonirradiated PSE pork after
Ketones
15867a 550c
3041c
761c
195c
335c
5308b 189c
218c
733
10 d of storage were found in aerobicb
a
b
b
b
b
b
b
b
Alcohols
2402
26350
4014
160
1192
0
420
370
52
86
Aldehydes
1055bc 763bc 1863a
472bc
844bc
684bc
633bc 1161b 399c
156 packaging conditions. After 10 d of storS-compounds
185d
1738c
65d
10037a 4643b 1274c 5143b 2979bc 2684c 592 age, the amounts of most volatile
Hydrocarbons 2167c 2066cd 1991cd
3918a 2403bc 1049e 3174ab 3112ab 1183de 253 groups (except for ketones) decreased
Total volatiles 23145b 32796a 11639cd 16905c 9830d 3727d 16125c 7379d 4937d 1944 (P ⬍ 0.05) from those at d 0, and the
Day 10
differences in irradiation effect by meat
Ketones
6040b
196c 3517bc 4357bc
0c
5718b 13128a 536c 1562bc 1248 type decreased. In particular, the
Alcohols
127c
7664a 3067bc
165c
4913b 1199c
238c 1608c 131c
879 amounts of S-containing volatiles in irAldehydes
276c
388ab
470ab
239c
845a
445ab
390ab 781ab 341bc 106
radiated samples decreased drastically,
S-compounds
139d
182d
112d
267d
632c
2146a
448c
387c 1169b
94
Hydrocarbons 1305c 1679c 1291c
1713c 5203a 1395c 1959c 3031b 1768c 294 and their differences among meat types
Total volatiles 8411b 10579ab 9294ab
7124b 12391ab 12519ab 16853a 7070b 6128b 1853 also disappeared except for the DFD
samples irradiated at 2.5 kGy. This result
a-e Different letters within a row are significantly different (P ⬍ 0.05), n = 4
SEM: Standard errors of the mean among different meat type x irradiation within a volatile group.
indicated that the volatiles produced by
irradiation were escaped during storage
under aerobic-packaging conditions.
The disappearance rate of S-containing
volatile compounds of irradiated DFD
Table 5—Sensory characteristics of aerobically packaged irradiated normal, pork was slower than that of the normal
PSE, and DFD pork Longissumus dorsi muscle refrigerated for 7 d
or PSE pork.
Irradiation
Off-odor intensity3
0 kGy
2.5 kGy
4.5 kGy
SEM2
Preference for the meat odor4
0 kGy
2.5 kGy
4.5 kGy
SEM2
Norm
PSE
DFD
2.90by
4.00ay
3.12by
6.91x
7.33x
0.32
6.72x
7.32x
0.34
6.47x
6.79x
0.32
9.12ax
7.12y
6.37y
0.33
8.14bx
6.75y
6.56y
0.33
9.36ax
7.44y
7.06y
0.34
SEM1
Sensory characteristics
0.26
0.35
0.36
0.33
0.31
0.35
a-b Different letters within a row are significantly different (P ⬍ 0.05), n = 76.
x-yDifferent letters within a column of the same question are significantly different ( P ⬍ 0.05).
1 SEM: Standard errors of the mean among different meat type within an irradiation dose.
2 SEM: Standard errors of the mean among different irradiation dose within a meat type.
3 Off-odor intensity: 0, no odor; 15, very strong odor.
4 Preference for the meat odor: 0, not preferable; 15, highly preferable.
SensoryandNutritiveQualitiesofFood
amounts of ketones and alcohols in
meat decreased significantly after irradiation. The production of sulfur-containing volatile compounds in pork increased
by
irradiation,
but
no
difference in S-compounds between 2.5
kGy and 4.5 kGy was observed. DFD
pork produced the least amount of Scontaining volatiles among the 3 meat
types at each irradiated and nonirradiated conditions (Table 4). The pH of the
meat system could have an important
role in producing S-containing volatile
compounds by irradiation. Shu and
others (1985) reported that a vigorous
thermal degradation of cysteine into
volatile components was occurring at
the isoelectric point of cysteine. The
major S-containing volatile compounds
found in irradiated pork include mer1228
captomethane, dimethyl sulfide, carbon
disulfide, methyl thioacetate, and dimethyl disulfide. Patterson and Stevenson
(1995) found that dimethyl trisulfide is
the most potent off-odor compound,
and the changes that occur following irradiation are distinctively different
from those of the warmed-over flavor
in oxidized meat. Ahn and others (2000)
reported that S-containing volatiles
such as 2,3-dimethyl disulfide produced
by radiolytic amino acids were responsible for the off odor in irradiated pork.
They also assumed that the off-odor
volatiles in irradiated pork were the result of compounding effects of volatiles
from lipid oxidation and other reactions, such as radiolysis of amino acid
side chains. The production of aldehydes and hydrocarbons in pork were
JOURNAL OF FOOD SCIENCE—Vol. 66, No. 8, 2001
Meat type and irradiation dose affected (P ⬍ 0.05) the intensity of off
odor and the preference for a meat
odor (Table 5). The off-odor intensity of
PSE was higher than normal and DFD
meats in nonirradiated samples. Irradiation increased (P ⬍ 0.05) the intensity
of irradiation odor, which was not significantly different among irradiated
normal, PSE, and DFD meats. The preference for a meat odor also was consistent with the result of intensity of off
odor. As the off odor in meat became
more intense, the preference for the
meat odor decreased because most
trained panelists considered irradiation
odor as an off odor. Huber and others
(1953) reported that meat sterilized by
irradiation developed a characteristic
odor, which has been described as metallic, sulfide, wet dog, wet grain, or
burnt.
In nonirradiated samples, the preference for a meat odor for normal and
DFD meats was higher than the PSE
meat. After irradiation, however, there
was no difference in odor preference
for the 3 pork types. Ahn and others
(2000) reported that sensory characteristics of irradiated meat were described
as having a barbecued corn-like odor,
and sensory panels showed no objection to the odor. However, irradiation
of pork at the 2.5 kGy level decreased
(P ⬍ 0.05) the odor preference for all 3
pork types in this study.
Irradiation Impact on the Quality of Pork with Different Ultimate pH . . .
I
RRADIATION INCREASED TBARS AND
off odor in aerobically packaged
pork. But DFD pork, which usually is
underutilized because of its microbial
susceptibility, was more stable and resistant to lipid oxidation and off-odor
production by irradiation than the normal pork. This suggests that irradiation
can significantly increase the utilization
of DFD pork, and can greatly benefit
pork and beef industries.
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MS 20000509
Journal Paper Nr J-18852 of the Iowa Agriculture and Home
Economics Experiment Station, Ames, IA 50011. Project Nr
3322, supported by the Food Safety Consortium.
Authors are with the Animal Science Dept., Iowa
State Univ., Ames, IA 50011-3150. Direct inquiries
to author Ahn (E-mail: duahn@iastate.edu).
Vol. 66, No. 8, 2001—JOURNAL OF FOOD SCIENCE
1229
SensoryandNutritiveQualitiesofFood
Conclusion