Meat Science 56 (2000) 203±209
www.elsevier.com/locate/meatsci
Quality characteristics of pork patties irradiated and stored in
di€erent packaging and storage conditions
D.U. Ahn *, C. Jo, M. Du, D.G. Olson, K.C. Nam
Department of Animal Science, Iowa State University, Ames, IA 50011-3150, USA
Received 1 February 2000; received in revised form 6 April 2000; accepted 6 April 2000
Abstract
Patties were made from pork loin, individually vacuum- or aerobic-packaged and stored either at 4 or ÿ40 C. Refrigerated patties were irradiated at 0, 1.5, 3.0 or 4.5 kGy absorbed dose, and frozen ones were irradiated at 0, 2.5, 5.0, or 7.5 kGy. Samples were
analyzed for lipid oxidation, volatile production and odor characteristics. Refrigerated samples were analyzed at 0, 1 and 2 weeks,
and frozen ones after 0, 1.5 and 3 months of storage. With vacuum packaging, the lipid oxidation (TBARS) of both refrigerated
and frozen patties was not in¯uenced by irradiation and storage time except for the patties irradiated and refrigerated at 7.5 kGy.
With refrigerated storage, panelists could detect irradiation odor at day 0, but not after 1 week at 4 C. With frozen storage, however, irradiation odor was detected even after 3 months of storage. With aerobic packaging, the TBARS of refrigerated pork patties
increased with storage time. The TBARS of pork patties increased as irradiation dose increased at day 0, but the e€ect disappeared
after 1 week at 4 C. Nonirradiated patties were preferred to the irradiated ones at day 0 because of the signi®cant irradiation odor
in the irradiated ones, but the o€-odor disappeared after 1 week at 4 C. With frozen storage, patties irradiated at 7.5 kGy had
higher TBARS than those irradiated at lower doses. Nonirradiated patties had higher preference scores than the irradiated ones for
1.5 months in frozen storage. Sulfur-containing compounds were responsible for most of the irradiation o€-odor, but these volatilized quickly during storage under aerobic conditions. Overall, vacuum packaging was better than aerobic packaging for irradiation
and subsequent storage of meat because it minimized oxidative changes in patties and produced minimal amounts of volatile
compounds that might be responsible for irradiation o€-odor during storage. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Irradiation; Storage temperature; Lipid oxidation; Odor; Volatile compounds
1. Introduction
The number of reported outbreaks of Escherichia coli
has increased rapidly and it is estimated to cause more
than 20,000 infections and 250 deaths each year (Boyce,
Swerdlow & Grin, 1995). Olson (1998) indicated that
low-dose (<10 kGy) irradiation can kill at least 99.9%
of salmonella in poultry and an even higher percentage
of E. coli O157:H7. The Food and Drug Administration
(FDA) approved irradiation for poultry and red meats
to control foodborne pathogens and extend product
shel¯ife (Gants, 1998). One of the major concerns with
irradiating meat, however, is its e€ect on lipid oxidation,
color and o€-odor production.
The mechanisms of lipid oxidation in irradiated meat
are not fully understood, but they are likely to be similar
* Corresponding author. Tel.: +1-515-294-6595; fax: +1-515-2949143.
E-mail address: duahn@iastate.edu (D.U. Ahn).
to those in nonirradiated meat. Therefore, the susceptibility of irradiated muscle tissues to lipid oxidation is
closely related to the nature, proportion, degrees of
saturation in fatty acids and the composition of phospholipids in cell membrane (Gray, Gomma & Buckley,
1996). Ang and Lyon (1990) reported that hexanal and
pentanal had a strong correlation with TBARS and o€odor related to lipid oxidation in meat. But, lipid oxidation
alone cannot produce the characteristic irradiation odor
because meat irradiated in an oxygen-impermeable
package, which theoretically stops lipid oxidation, still
produces irradiation odor.
Ahn, Jo and Olson (1999) suggested that volatile
compounds responsible for o€-odor in irradiated meat
are produced by radiation impact on protein and lipid
molecules and are di€erent from those of lipid oxidation. Patterson and Stevenson (1995) showed that
dimethyltrisul®de is the most potent o€-odor compound
in irradiated raw chicken meat. Our recent study (Jo &
Ahn, 2000) showed that irradiation produced characteristic volatile compounds from a meat model system
0309-1740/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0309-1740(00)00044-9
204
D.U. Ahn et al. / Meat Science 56 (2000) 203±209
containing leucine, valine, isoleucine, phenylalanine,
methionine or cysteine by radiolytic degradations. This
indicated that both radiolysis of proteins and lipid oxidation are important for o€-odor generation in irradiated
meat. But, the quality changes in irradiated raw meat
with di€erent packaging and storage conditions are not
clear yet. The objective of this study was to elucidate the
e€ect of di€erent doses of irradiation on lipid oxidation,
odor and volatile compound production in vacuum- or
aerobic-packaged pork patties during refrigerated or
frozen storage.
2. Materials and methods
2.1. Sample preparation and irradiation
Pork loins were purchased (less than 4 days after
slaughter) from four di€erent local stores and were
individually ground twice through a 9-mm plate. Patties
(approximately 80 g each) were made and packaged in
bags of two di€erent packaging materials: one half of the
patties were packaged (ÿ1.0 bar) in oxygen-impermeable
nylon/polyethylene bags (9.3 ml O2/m2/24 h at 0 C; Koch,
Kansas City, MO) and the other half in oxygen-permeable
polyethylene zipper bags (46, 2 MIL, Associated Bag
Company, Milwaukee, WI). To minimize oxidative changes
between sample preparation and delay before irradiation,
those patties packaged with oxygen-permeable bags
were repackaged in large vacuum-packaging bags (eight
to 10 small packs per large vacuum-packaging bag, ÿ1.0
bar). One half of the patties packaged each in oxygenpermeable bags and in oxygen-impermeable bags were
stored in a 4 C cooler and the other half in a ÿ40 C
freezer overnight. The next day, individually packaged
patties were removed from the big vacuum packs and
placed in a single layer on carts. An electron-beam irradiation was performed using a Linear Accelerator (Circe
IIIR, Thomson CSF Linac, Saint-Aubin, France). The
target doses of refrigerated pork patties were 0, 1.5, 3.0
and 4.5 kGy and those of frozen patties were 0, 2.5, 5.0
and 7.5 kGy. The energy and power level used were 10
MeV and 10 kw, respectively, and the average dose rate
was 98.0 kGy/min. The max/min ratio was approximately 1.130.14 for 2.5 kGy, 1.110.18 for 4.5 kGy,
and 1.090.12 for 7.5 kGy. To con®rm 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 (Bruker Instruments Inc., Billerica, MA).
2.2. Lipid oxidation
The ¯uorescence 2-thiobarbituric reactive substances
(TBARS) method (Jo & Ahn, 1998) was used to determine the extent of lipid oxidation in raw meat patties.
Sample (5 g) was taken into a test tube (50 ml), 15 ml of
deionized distilled water (DDW) was added, and
homogenized with a Brinkmann polytron (Type PT 10/
35, Brinkmann Instrument Inc., Westbury, NY) for 10 s
at high speed. The meat homogenate (0.5 ml), sodium
dodecylsulfate (8.1%, 200 ml), hydrochloric acid (0.5 M,
1.5 ml), thiobarbituric acid (20 mM, 1.5 ml), butylated
hydroxytoluene (7.2%, 50 ml) and DDW (250 ml) were
added into 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 nbutanol/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 used for ¯uorescence reading.
2.3. Volatile compound analysis
A Precept II and a Purge-and-Trap concentrator 3000
(Tekmar-Dohrmann, Cincinnati, OH) were used to
purge and trap volatile compounds as described by Ahn
et al. (1999), with some modi®cations. A gas chromatograph (GC, Model 6890, Hewlett Packard Co., Wilmington, DE) equipped with a mass selective detector
(MSD, Model 5973, Hewlett Packard Co.) was used to
qualify and quantify volatile compounds. Sample (3 g)
was transferred to a 40-ml sample vial, and headspace
was ¯ushed with helium gas (99.999% purity) for 5 s to
minimize oxidative changes in meat during the waiting
period before analysis. Sample was purged with helium
(40 ml/min) for 14 min at 40 C. Volatile compounds
were trapped using a Tenax/silica/charcoal column
(Tekmar-Dohrmann) and desorbed into a column in the
GC for 1 min at 220 C. A modi®ed column was used to
improve separation of volatile compounds. An HP-Wax
(7.5 m, 250 mm i.d., 0.25 mm nominal) column was
combined with an HP-5 column (30 m, 250 mm i.d., 0.25
mm nominal) using a Glass Press-®t connector (Hewlett
Packard Co.). A split inlet (split ratio, 49:1, inlet temperature 175 C) was used to inject volatile compounds
into the column and a ramped oven temperature was
used (7 C for 2.5 min, increased to 25 C at 3 C/min, to
120 C at 10 C/min, and to 200 C at 20 C/min). Liquid
nitrogen was used to cool the oven below the ambient
temperature. Helium was the carrier gas at a constant
¯ow of 1.2 ml/min. The temperature of transfer lines
was maintained at 155 C. The ionization potential of
MS was 70 eV; the scanned mass range was 46.1 to 550
to eliminate carbon dioxide peak, and the scan velocity
was 2.94 scan/s. The identi®cation of volatile compounds was achieved by comparing mass spectral data
with those of the Wiley library (Hewlett Packard Co.).
Selected standards were used to verify the identities of
some volatiles. Each individual standard was diluted
with methanol, put in a 40-ml sample vial of the Precept
II, purged and analyzed using the same method used for
D.U. Ahn et al. / Meat Science 56 (2000) 203±209
meat samples. n-Hexanal and 2,3-dimethyldisul®de were
purchased from Chromatography Research Supplies
Inc. (Addison, IL) and Aldrich (Milwaukee, WI),
respectively. The peak area (total ion counts103) was
reported as the amount of volatile compounds released.
2.4. Odor intensity and preference
An 11-member trained panel was used to evaluate the
irradiation odor intensity and odor preference of both
refrigerated and frozen pork loin patties. Training was
performed at the initial stage for panelists to be able to
determine characteristic irradiation odor and intensity
using fresh pork patties irradiated at 5 and 10 kGy.
Refrigerated patties were tempered about 20 min at
room temperature (22 C) and frozen patties were
thawed for 2 h at 22 C before presenting them to the
sensory panel. Samples (3 g) were presented in a tightly
capped scintillation vial (20 ml) and a 15-cm linear scale
was used to rate the samples on each sensory attribute.
Three questions were asked: irradiation odor intensity
(very weak=0 and very strong=15) odor preference
(highly acceptable=0 and not acceptable=15), and
odor description. Panelists were given a sucient time
(20 min or more) to evaluate four samples.
2.5. Statistical analysis
Two-way Analyses of Variance (SAS, 1989) was used
to determine the e€ect of irradiation dosage and storage
conditions on the quality parameters of pork loin. Pork
loins purchased from each of four di€erent stores were
used as replication, and signi®cance level was determined
at P<0.05. The Student±Newman±Keul's multiple
range test was used to compare di€erences among mean
values. Mean values and standard errors of the means
(S.E.M.) were reported.
3. Results and discussion
3.1. Lipid oxidation
The TBARS of vacuum-packaged patties irradiated at
1.5, 3.0 or 4.5 kGy and stored at 4 C were not much di€erent from those of the nonirradiated control at each storage
time. However, the TBARS value of pork patties stored at
4 C for 1 week showed the highest among all storage periods. Vacuum packaging changes the gaseous environment
at the meat surface: respiration of microorganisms at the
meat surface or the meat itself produces CO2 and eventually the oxygen concentration within the pack falls below
1% while the CO2 concentration rises to 20% or more
(Eustace, 1981). The compositional changes of gas could
have involved the control of oxygen-dependent microorganisms or oxidative degradation of meat in the bag.
205
The patties that were aerobic-packaged and irradiated
at 4.5 kGy had higher TBARS values than those irradiated at 1.5 kGy or the nonirradiated control (Table 1)
at Day 0. The TBARS values increased sharply during
refrigerated storage in aerobic packaging, but the e€ect
of irradiation was not found at 2 weeks of storage. This
result agreed with our previous work (Jo, Lee & Ahn,
1999) and could be interpreted as showing that storage
condition or oxygen availability was more important for
the development of lipid oxidation than irradiation.
With frozen storage, the TBARS of pork patties irradiated at 7.5 kGy was higher than that of the nonirradiated control at day 0, but was not di€erent after
1.5 and 3 months of storage (Table 2). Jo and Ahn
(2000) also reported that the TBARS was higher in
irradiated, vacuum-packaged pork sausage at 4.5 kGy
dose at ®rst, but the irradiation e€ect disappeared during
storage. Luchsinger et al. (1997) showed that TBARS
values of both chilled and frozen boneless pork chops
were stable, regardless of display day, dose and irradiation sources. Aerobic-packaged patties irradiated at 7.5
kGy had the highest TBARS, and the sample irradiated
at 5 kGy had higher TBARS than those with 2.5 kGy or
nonirradiated control during frozen storage (Table 2).
TBARS decreased in patties irradiated at 2.5 and 7.5
kGy during the 3-month frozen storage, but the changes
were small. This result indicated that the radiation
chemistry of refrigerated and frozen meat could be different. Tarte (1996) reported that temperature has signi®cant e€ects on the formation of radiolytic products,
and that the reactive intermediates of water radiolysis
were trapped in deep-frozen materials and thus were
kept from reacting with each other or with the substrates. During the warming process, however, they tend
to react with each other rather than with the substrates
(Diehl, 1995).
3.2. Irradiation odor intensity and odor preference
Sensory tests indicated that the panel clearly detected
irradiation odor from irradiated and refrigerated pork
patties at day 0, but could not separate irradiation dose
e€ect in both vacuum-and aerobic-packaged patties
(Table 3). Rating samples that were in refrigerated storage
for 1 and 2 weeks, the panel rated the intensity of irradiation odor in nonirradiated samples as high, indicating
that by-products from lipid oxidation or other chemical
reactions could mislead the panelists. The fact that
nonirradiated pork patties stored for 1 or 2 weeks
scored higher irradiation odor than the irradiated ones
at day 0 supported this interpretation (Table 3).
Although vacuum packaging minimized oxygen contact
with pork patties, the residual oxygen inside of the bag
and transferred oxygen from outside through the
packaging ®lm could be responsible for the development
of a certain degree of lipid oxidation and odor changes.
206
D.U. Ahn et al. / Meat Science 56 (2000) 203±209
Table 1
TBARS values (mg malondialdehyde/kg meat) of pork patties irradiated and stored at 4 Ca,b
Irradiation dose (kGy)
Vacuum packaging
Aerobic packaging
Storage (week)
0
1.5
3.0
4.5
S.E.M.c
0
1.5
3.0
4.5
S.E.M.
0
1
2
0.08c
0.22a
0.14b
0.08c
0.21a
0.12b
0.09b
0.24a
0.15b
0.10b
0.32a
0.16b
0.01
0.03
0.01
0.08by
0.34a
0.40a
0.07cy
0.45b
0.85a
0.11cxy
0.43b
0.65a
0.12cx
0.43b
0.82a
0.01
0.06
0.12
0.02
0.01
0.02
0.02
0.03
0.08
0.07
0.10
S.E.M.
a
b
c
Means with a di€erent letter (a±c) within a column of the same sensory category is di€erent (P < 0.05).
Means with a di€erent letter (x,y) within a row with the same packaging method is di€erent (P < 0.05).
S.E.M., standard errors of the mean.
Table 2
TBARS values (mg malondialdehyde/kg meat) of pork patties irradiated and stored atÿ40 Ca,b
Irradiation dose (kGy)
Vacuum packaging
Aerobic packaging
Storage (month)
0
2.5
5.0
7.5
S.E.M.c
0
2.5
5.0
7.5
S.E.M.
0
1.5
3
0.15y
0.16
0.13
0.18xy
0.18
0.14
0.21xy
0.18
0.15
0.23ax
0.20ab
0.12b
0.02
0.02
0.02
0.15z
0.15y
0.11z
0.19az
0.21ay
0.12bz
0.29y
0.28x
0.24y
0.39ax
0.32abx
0.26bx
0.03
0.02
0.03
S.E.M.
0.01
0.01
0.02
0.02
0.01
0.02
0.03
0.03
a
b
c
Means with a di€erent letter (a,b) within a column of the same sensory category is di€erent (P < 0.05).
Means with a di€erent letter (x,y) within a row with the same packaging method is di€erent (P < 0.05).
S.E.M., standard errors of the mean.
Table 3
Irradiation odor intensitya and odor preferenceb of pork patties irradiated and stored at 4 Cc,d
Irradiation dose (kGy)
Vacuum packaging
Storage (week)
1.5
3.0
4.5
S.E.M.e
0
1.5
3.0
4.5
S.E.M.
10.3x
9.8
9.0
10.7x
10.3
9.6
9.9x
10.6
9.8
1.0
1.1
1.0
1.9y
5.7
6.5
7.8x
5.5
6.6
9.4x
6.6
5.4
7.7x
6.4
7.1
1.2
1.3
1.4
1.3
0.8
1.0
1.0
1.3
1.2
1.3
1.4
7.1b
13.2a
10.5ab
10.1
11.1
8.1
9.4
11.5
9.0
9.3
9.2
8.9
3.8by
7.9a
8.8a
9.4x
7.8
9.9
9.5ax
8.1ab
5.7b
8.7x
7.2
6.9
1.2
1.1
1.2
1.3
1.1
1.2
1.1
1.1
0
Irradiation odor intensity
0
2.9by
1
9.5a
2
8.9a
S.E.M.
Odor preference
0
1
2
S.E.M.
a
b
c
d
e
Aerobic packaging
1.3
1.2
1.2
0, very weak; 15, very strong.
0, strongly like; 15, strongly dislike.
Means with a di€erent letter (a,b) within a column of the same sensory category is di€erent (P < 0.05).
Means with a di€erent letter (x,y) within a row with the same packaging method is di€erent (P < 0.05).
S.E.M., standard errors of the mean.
1.1
1.1
1.1
D.U. Ahn et al. / Meat Science 56 (2000) 203±209
207
Generally, frozen patties with aerobic packaging were
described as bland and had no strong odor as did
vacuum-packaged or refrigerated pork patties.
No irradiation dose e€ect was found on the odor preference of pork patties with vacuum packaging (Table
3), but panelists preferred the odor of aerobic-packaged,
nonirradiated samples to that of irradiated ones at day 0.
Nonirradiated patties stored for 1 or 2 weeks in vacuum
and aerobic packaging showed lower odor preference
(higher score) than those of the day 0 (Table 3).
Irradiation odor intensity increased in a dose-dependent
manner in vacuum-packaged and frozen pork patties
(Table 4). Irradiation odor lasted longer in frozen than
in refrigerated pork patties and panelists could detect
irradiation odor even after 3 months of frozen storage.
Little changes in the TBARS of frozen samples during
storage indicated that lipid oxidation may not be the
major cause of irradiation o€-odor. Panelists also
detected irradiation odor in aerobic-packaged frozen
samples at day 0, and the irradiation odor lasted for 1.5
months (Table 4). Panel preferred nonirradiated patties
to irradiated ones until 1.5 months of frozen storage,
which coincided with the intensity of irradiation odor in
pork patties. Panelists characterized vacuum-packaged,
irradiated and frozen meat odor as the following: rotten
egg, sweet, bloody, cooked meat or barbecued corn,
burnt, sulfur, metallic, alcohol or acidic. Those words
were also found in other studies (Heath, Owens, Tesch
& Hannah, 1990; Huber, Brasch & Waly, 1953). Similar
odor description was obtained from aerobic-packaged,
irradiated and refrigerated pork at 0 weeks, but other
sensory traits such as sour, pungent, spicy, acidic and/or
rancid appeared after 1 week of storage, probably
because of volatile compounds formed by microbial and
oxidative degradation of fat and other meat components.
3.3. Volatile compound analysis
Pork patties irradiated at 4.5 kGy and refrigerated for
1 week produced higher n-hexanal than other irradiation
doses with vacuum packaging (Table 5), but the amount
of n-hexanal in patties nonirradiated or irradiated at 1.5
kGy increased at 1 and 2 weeks of storage. Irradiation
had no e€ect on the production of n-hexanal in refrigerated, aerobic-packaged pork patties. Storage in
aerobic conditions, however, signi®cantly increased the
production of n-hexanal in all irradiated pork patties
(Table 5). This indicates that oxygen availability is
important for the progress of oxidative chain-reactions.
Jo et al. (1999) indicated that both TBARS and volatile
compounds in meat should be used to determine oxidative changes in irradiated meat accurately because the
amount of hexanal decreased after 3 days of storage in
both aerobic and vacuum packaging. Ahn et al. (1999)
reported that irradiated muscle strips produced a few
volatile compounds that were not found in nonirradiated meat. Most of them were sulfur-containing
compounds and the amount of 2,3-dimethyldisul®de
was the highest. Jo and Ahn (2000) reported that 2,3dimethyldisul®de was produced from irradiated oil
emulsion containing methionine. The amount of 2,3dimethylsul®de in refrigerated and vacuum-packaged
pork patties at 0 time rapidly increased with the increase
of irradiation doses (Table 5), but nonirradiated sample
Table 4
Irradiation odor intensitya and odor preferenceb of pork patties irradiated and stored atÿ40 Cc,d
Irradiation dose (kGy)
Vacuum packaging
Aerobic packaging
2.5
5.0
7.5
S.E.M.e
0
Irradiation odor intensity
0
1.5az
1.5
5.1b
3
2.9aby
4.6yz
5.4
6.0xy
7.3xy
8.6
7.7x
10.4x
8.5
9.6x
1.1
1.1
1.3
1.1by
2.0by
5.8a
4.8x
8.7x
7.5
S.E.M.
0.8
1.3
1.2
1.4
0.9
1.3
Odor preference
0
1.5
3
3.5by
7.3a
6.4a
6.8xy
7.3
6.5
8.2x
8.6
7.6
9.2x
8.2
9.3
S.E.M.
0.9
1.2
1.1
1.4
Storage (month)
a
b
c
d
e
0
1.2
0.8
1.3
3.1by
6.2aby
8.3a
1.1
2.5
6.0bxy
10.3ax
8.2ab
1.1
0, very weak; 15, very strong.
0, strongly like; 15, strongly dislike.
Means with a di€erent letter (a,b) within a column of the same sensory category is di€erent (P < 0.05).
Means with a di€erent letter (x,y) within a row with the same packaging method is di€erent (P < 0.05).
S.E.M., standard errors of the mean.
5.0
7.5
S.E.M.
7.8x
7.3x
6.9
7.7x
7.9x
8.9
1.2
1.1
1.3
1.4
1.4
7.3bx
10.0ax
6.3b
1.0
7.8x
7.8xy
8.2
1.2
1.1
1.0
1.1
208
D.U. Ahn et al. / Meat Science 56 (2000) 203±209
signi®cantly from day 0 because of the high volatility of
this odor compound. Patterson and Stevenson (1995)
suggested that dimethyltrisul®de was the primary contributor to the irradiation o€-odor in meat.
The amount of hexanal in irradiated sample was not
changed during the 3 months of frozen storage in
vacuum packaging except for the pork patties irradiated
at 5 kGy (Table 6). However, irradiation increased the
hexanal content in frozen samples. It demonstrates that
irradiation can accelerate lipid oxidation in meat to
produced no 2,3-dimethyldisul®de. During the 2-week
storage, the amount of 2,3-dimethyldisul®de decreased
signi®cantly except for the samples irradiated at 1.5
kGy. The pork patties with aerobic packaging also
showed that the amount of 2,3-dimethyldisul®de in
irradiated meat at 0 time increased dramatically with
the increase of irradiation doses, but vacuum-packaged
patties retained more 2,3-dimethyldisul®de than aerobic-packaged ones (Table 5). After 2 weeks of storage at
4 C, the amount of 2,3-dimethyldisul®de decreased
Table 5
n-Hexanal and 2,3-dimethyldisul®de production (ion count1000) of pork patties irradiated and stored at 4 Ca,b
Irradiation dose (kGy)
Vacuum packaging
Aerobic packaging
Storage (week)
0
1.5
3.0
4.5
S.E.M.c
0
1.5
3.0
4.5
S.E.M.
n-Hexanal
0
1
2
0b
35ay
26ab
0b
43ay
29a
30
59xy
134
21
116x
253
8
19
98
54b
173b
634a
31a
160ab
306b
46b
299b
1923a
48b
812ab
1976a
8
240
442
S.E.M.
9
7
60
97
138
52
397
397
2,3-Dimethyldisul®de
0
0z
1
0
2
0y
255z
142
72y
5338ay
104b
871by
10239ax
1670b
3946bx
0z
0y
0y
430az
55bxy
25bxy
3498ay
50bxy
64bx
6706ax
77bx
73bx
S.E.M.
166
563
1040
±
70
321
153
a
b
c
±
297
742
657
313
16
15
Means with a di€erent letter (a,b) within a column of the same sensory category is di€erent (P < 0.05).
Means with a di€erent letter (x±z) within a row with the same packaging method is di€erent (P < 0.05).
S.E.M., standard errors of the mean.
Table 6
n-Hexanal and 2,3-dimethyldisul®de production (ion count1000) of pork patties irradiated and stored at ÿ40 Ca,b
Irradiation dose (kGy)
Vacuum packaging
Aerobic packaging
Storage (month)
0
2.5
5.0
7.5
n-Hexanal
0
1.5
3
0z
0y
0y
52y
52y
110xy
55by
92by
260ax
99x
270x
270x
S.E.M.
±
19
49
2,3-Dimethyldisul®de
0
1.5
3
0
0
0
0
607
0
S.E.M.
±
350
a
b
c
S.E.M.c
0
2.5
5.0
7.5
S.E.M.
10
44
43
0by
0by
96az
74by
154ay
188ayz
99by
857ax
302by
288bx
1190ax
555bx
30
134
42
48
24
18
42
158
121
830
0
1605
150
0
414
374
±
0z
0y
0y
0bz
121ay
0y
48y
502xy
0y
127x
1100x
96x
12
257
17
251
479
8
115
275
±
Means with a di€erent letter (a,b) within a column of the same sensory category is di€erent (P < 0.05).
Means with a di€erent letter (x±z) within a raw with the same packaging method is di€erent (P < 0.05).
S.E.M., standard errors of the mean.
D.U. Ahn et al. / Meat Science 56 (2000) 203±209
some extent in vacuum-packaged conditions. Similarly,
the amount of hexanal in aerobically-packaged, irradiated and frozen samples was higher than that of the
nonirradiated samples with the same packaging and
storage conditions (Table 6). The hexanal content in
nonirradiated patties or irradiated ones at 2.5 kGy
increased during storage. However, the amount of hexanal in patties irradiated at 5.0 and 7.5 kGy increased at
1.5 months and decreased at 3 months of storage, which
could be caused by further oxidation of hexanal to hexanoic acid during the longer-term storage.
The amount of 2,3-dimethyldisul®de in the patties
stored at frozen conditions was relatively small and
mostly disappeared during the 3-month storage (Table 6).
No irradiation dose e€ect was found on the production of
2,3-dimethyldisul®de from vacuum-packaged, frozen
pork patties except for day 0, mainly because of large
variation in its content among replications (Table 6). In
addition to 2,3-dimethyldisul®de, several other irradiation-dependent volatile compounds such as 2-propenal,
methanethiol, and 2,3-dimethyltriul®de, 2-methylbutanal and 3-methylbutanal were also found.
4. Conclusion
The use of vacuum packaging is more bene®cial than
the use of aerobic packaging for irradiated meat because
vacuum packaging minimizes oxidative changes. Aerobic packaging is not a good practice for the long-term
storage of meat. But, aerobic packaging may be useful
for short-term storage of irradiated pork patties because
compounds that are responsible for irradiation o€-odor
can be reduced during the storage period.
Acknowledgements
Journal Paper No. J-18758 of the Iowa Agriculture
and Home Economics Experiment Station, Ames, IA.
Project No. 3322, and supported by the Food Safety
Consortium.
209
References
Ahn, D. U., Jo, C., & Olson, D. G. (1999). Analysis of volatile components and the sensory characteristics of irradiated raw pork. Meat
Science, 54, 209±215.
Ang, C. Y. W., & Lyon, B. G. (1990). Evaluation of warmed-over
¯avor during chill storage of cooked broiler breast, thigh and skin
by chemical, instrumental and sensory methods. Journal of Food
Science, 55, 644±648. 673.
Boyce, T. D., Swerdlow, D. L., & Grin, P. M. (1995). Escherichia
coli O157:H7 and the Hemolytic-Uremic Syndrome. New England
Journal of Medicine, 333, 364±368.
Diehl, J. F. (1995). Safety of irradiated foods (2nd ed.). New York:
Marcel Dekker Inc.
Eustace, I. J. (1981). Some factors a€ecting oxygen transmission rates
of plastic ®lms for vacuum packaging of meat. Journal of Food
Technology, 16(1), 73±80.
Gants, R. (1998). Irradiation: weighing the risks and bene®ts. Meat
and Poultry, April, 34±42.
Gray, J. I., Gomma, E. A., & Buckley, D. J. (1996). Oxidative quality
and shelf-life of meats. Meat Science, 43, S111±S123.
Heath, J. L., Owens, S. L., Tesch, S., & Hannah, K. W. (1990). E€ect
of high-energy electron irradiation of chicken on thiobarbituric acid
values, shear values, odor, and cook yield. Poultry Science, 69, 313±
319.
Huber, W., Brasch, A., & Waly, A. (1953). E€ect of processing conditions on organoleptic changes in foodstu€s sterilized with high
intensity electrons. Food Technology, 7, 109±115.
Jo, C., & Ahn, D. U. (1998). Fluorometric analysis of 2-thiobarbituric
acid reactive substances in turkey. Poultry Science, 77, 475±480.
Jo, C., & Ahn, D. U. (2000). Production of volatile compounds from
irradiated oil emulsion containing amino acids or proteins. Journal
of Food Science (In press).
Jo, C., Lee, J. I., & Ahn, D. U. (1999). Lipid oxidation, color, and
volatile changes in irradiated pork sausages with di€erent fat content and packaging during storage. Meat Science, 51, 355±361.
Luchsinger, S. E., Kropf, D. H., Garcia-Zepeda, C. M., Hunt, M. C.,
Stroda, S. L., Marsden, J. L., & Kastner, C. L. (1997). Color and
oxidative properties of irradiated ground beef patties. Journal of
Muscle Foods, 8, 445±464.
Olson, D. G. (1998). Irradiated food. Food Technology, 52, 56±62.
Patterson, R. L. S., & Stevenson, M. H. (1995). Irradiation-induced
o€-odor in chicken and its possible control. British Poultry Science,
36, 425±441.
SAS (1989). SAS user's guide1. Statistical Analysis Institute Institute.
NC: Cary.
Tarte, R. (1996). Sensitivity of Listeria to irradiation in raw ground
meat, as a€ected by type of radiation, products temperature,
packaging atmosphere and recovery medium. PhD dissertation,
Iowa State University, Ames, IA.