Meat Science 54 (2000) 209±215
www.elsevier.com/locate/meatsci
Analysis of volatile components and the sensory characteristics of
irradiated raw pork
$
D.U. Ahn*, C. Jo, D.G. Olson
Department of Animal Science, Iowa State University, Ames, IA 50011-3150, USA
Received 22 March 1999; accepted 11 June 1999
Abstract
Longissimus dorsi muscle strips, approximately 20 mm long, 40 mm wide, and 5 mm thick (4 g), of pig were randomly placed in a
single layer into labeled bags (four strips per bag) and packaged either aerobically or under vacuum. Samples in the bags were
irradiated at 0, 5, or 10 kGy and stored at 4 C for 5 days. Lipid oxidation, the amount and identity of volatile components and
sensory characteristics of raw pork strips were determined at 0 and 5 days of storage. Irradiated muscle strips produced more 2thiobarbituric acid reactive substances (TBARS) than nonirradiated only in aerobic packaging during storage. Irradiation had no
e€ect on the production of volatiles related to lipid oxidation, but produced a few sulfur-containing compounds not found in
nonirradiated meat. This indicates that the major contributor of o€-odor in irradiated meat is not lipid oxidation, but radiolytic
breakdown of sulfur-containing amino acids. Many of the irradiation-dependent volatiles reduced to 50 to 25% levels during the 5days storage under aerobic conditions. Irradiated muscle strips produced stronger irradiation odor than nonirradiated, but no
irradiation dose or storage e€ect was found. Irradiation had no negative e€ect on the acceptance of meat, and approximately 70%
of sensory panels characterized irradiation odor as barbecued-corn-like odor. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction
Buzby and Roberts (1995) reported that microbial
pathogens in food cause between 6.5 million and 33
million cases of human illness and up to 9000 deaths in
the United States each year, and the estimated annual
cost of human illness caused by food-borne pathogens
ranges from $5.6 billion to $9.4 billion. Irradiation is
among the best known methods for control of potentially pathogenic microorganisms in raw meat (Gants,
1996). Although recent consumer surveys and market
analysis indicated that about 70% of consumers were
willing to pay a premium price for irradiated chicken
breast (Hayes, Shogren, Fox & Kliebenstein, 1995), one
of the major concerns in irradiating meat is its e€ect on
the generation of o€-odor and lipid oxidation, either of
which can impact negatively upon acceptance of such
Journal paper no. J-18261 of the Iowa agriculture and home economics experiment station, Ames, IA. Project no. 3322, and supported
by the National Pork Producers Council.
* Corresponding author. Tel.: +1-515-294-6595; fax: +1-515-2949143.
E-mail address: duahn@iastate.edu (D.U. Ahn).
$
treated meat products in the marketplace. Considering a
series of recent outbreaks of pathogenic bacteria in
meat, the expanded application of irradiation technology in meat and meat products becomes especially
important to improve safety and public con®dence. Little
attention, however, has been paid to these quality
aspects of meat in irradiation studies, especially at lowdose irradiation (<10 kGy).
Huber, Brash and Waly (1953) reported that sterilized
meat through irradiation developed a characteristic
odor, which has been described as metallic, sul®de, wet
dog, wet grain, or brunt. They assumed that the o€odor was the result of free radical oxidation that was
initiated by the irradiation process. Patterson and Stevenson (1995) found that dimethyltrisul®de is the most
potent o€-odor compound, and the changes that occur
following irradiation are distinctly di€erent from those
of warmed-over ¯avor in oxidized meat. Thayer, Fox
and Lakritz (1993) reported that irradiation dose, processing temperature, and packaging conditions strongly
in¯uence microbial and nutritional quality of meat.
Heath, Owens, Tesch and Hannah (1990) reported that
irradiating uncooked chicken breast and thigh at 2 or 3
kGy produced a hot fat, burned oil, or burned feathers
0309-1740/99/$ - see front matter # 1999 Elsevier Science Ltd. All rights reserved.
PII: S0309-1740(99)00081-9
210
D.U. Ahn et al. / Meat Science 54 (2000) 209±215
odor that remained after the thighs were cooked.
Hashim, Resurreccion and MaWatters (1995) reported
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.
Irradiation-induced oxidative chemical changes are
dose-dependent, and the presence of oxygen has a signi®cant e€ect on the rate of oxidation (Katusin-Razem,
Mihaljevic & Razen 1992). Diehl (1995) indicated that
there is a substantial di€erence between the radiation
chemistry of pure substances and of the same substances
when they are components of complex food systems.
The di€erences, however, are mostly quantitative,
rather than qualitative. Ahn, Olson, Jo, Chen, Wu and
Lee (1998a) indicated that irradiated meat, regardless of
packaging methods, produced more volatiles than nonirradiated patties and developed a characteristic aroma
after irradiation. Raw meat has very strong antioxidant
e€ects unless it is heated, denatured, or contains added
prooxidants. Irradiation accelerated lipid oxidation of
raw pork patties when stored in oxygen-permeable bags
during and after irradiation (Ahn et al., 1998). Chen, Jo,
Wu, Lee and Ahn (1999) reported that irradiation
before cooking did not in¯uence lipid oxidation of
cooked pork during storage. Cooked meat, however, is
highly susceptible to lipid oxidation because the cooking
process denatures antioxidant components, damages
cell structure, and exposes membrane lipids to the
environment (Ahn, Olson, Lee, Jo, Chen and Wu,
1998b). Irradiation dose a€ected production of volatiles
in vacuum- and aerobic-packaged cooked pork sausage,
but its e€ect on 2-thiobarbituric acid reactive substances
(TBARS) was minor (Ahn et al., 1998b).
The objectives of this study are to identify and quantify volatile compounds produced in raw pork by irradiation, and to determine sensory characteristics of
irradiated raw pork.
2. Materials and methods
2.1. Sample preparation
Longissimus dorsi muscles from four di€erent pigs
were obtained within 48 h after slaughter and used for
the irradiation treatments and sample analysis. Muscle
strips, approximately 20 mm long, 40 mm wide and
5 mm thick (4 g), were prepared. Four muscle strips
(one strip per each pig) were placed in a single layer into
each labeled bag and either aerobic or vacuum packaged. Polyethylene oxygen permeable bags were used
for aerobic packaging and nylon/polyethylene bags (9.3
mL O2/m2/24 h at 0 C; Koch, Kansas City, MO) were
used for vacuum packaging. Samples in the bags were
irradiated at 0, 5, or 10 kGy and stored at 4 C for
5 days. The meat from each of the four pigs represented
four experimental replications. Fluorescence TBARS
method (Jo & Ahn, 1998) was used to analyze lipid
oxidation, and a purge-and-trap/gas chromatographymass spectrometry (GC±MS) method was used to determine the amount and identity of volatiles components.
2.2. Volatile compounds analysis
A purge-and-trap apparatus connected to a GC unit
was used to analyze the volatiles potentially responsible
for the o€-odor in meat. Precept II and Purge-and-Trap
Concentrator 3000 (Tekmar-Dorham, Cincinnati, OH)
were used to purge and trap volatiles from the samples.
A GC unit (Model 6890, Hewlett Packard Co., Wilmington, DE) equipped with a mass selective detector
(MSD, HP 5973, Hewlett Packard) was used to characterize and quantify the volatile compounds in¯uenced
by headspace oxygen during sample holding periods. A
®ve-gram sample was used for raw meat and a threegram sample was used for cooked meat analyses. Meat
sample was placed in a sample vial (40 ml) and purged
with helium gas (40 ml/min) for 15 min. Volatiles were
trapped at 30 C using a Tenax/Silica gel/Charcoal column (Tekmar-Dorham) and desorbed for 1 min at
220 C. A split inlet (split ratio, 39:1) was used to inject
volatiles into a GC column (HP-5MS capillary column,
0.25-mm i.d., 30 m, and 0.25-mm ®lm thickness, Hewlett
Packard), and ramped oven temperature conditions
(30 C for 2 min, increased to 40 C @ 2 C/min,
increased to 50 C @ 5 C/min, increased to 100 C @
10 C/min, increased to 140 C @ 20 C/min, increased to
200 C @ 30 C/min, and held for 4.5 min) were used.
Inlet temperature was 180 C. Helium was used as a
carrier gas, and column ¯ow was 1.1 ml/min. The ionization potential of MS was 70 eV, scan range was 45 to
400 m/z, and scan velocity was 3.21 scan/s. The identi®cation of volatiles was achieved by comparing mass
spectral data with those of the Wiley library (Hewlett
Packard). The area of each peak was integrated using
ChemStation software (Hewlett Packard), and total ion
counts 103 was reported as an indicator of volatiles
generated from the meat samples.
2.3. Sensory analysis
The intensity and descriptive characteristics of odor
of meat samples were determined using 13 trained sensory panelists. 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 evaluation of odor, samples in coded, capped scintillation vials
(glass) 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
D.U. Ahn et al. / Meat Science 54 (2000) 209±215
odor', and `not acceptable' and `highly acceptable' at
opposite ends, were used to rate the samples on the
intensity of irradiation odor and acceptance of irradiation odor. The responses from the panelists were
expressed in numerical values ranging from 0 (no irradiation odor or not acceptable) to 15 (strong irradiation
odor or highly acceptable) to the nearest 0.5 cm. Sensory panels were also asked to characterize the odor
that best describe it. The relationship between lipid
oxidation, volatile composition, and odor intensity
and characteristics was evaluated using correlation
coecients.
2.4. Statistical analysis
The experiment was designed primarily to determine
the e€ect of irradiation dose on lipid peroxidation,
volatiles, and o€-odor production in muscle strips with
di€erent packaging. The TBARS, volatiles, and o€odor production of raw pork were analyzed independently by SAS software (SAS Institute, 1989). Analyses
of variance were conducted to test the e€ects of
irradiation dose and packaging, and the Student±Newman±Keuls multiple range test was used to compare
di€erences among mean values. The relationship
between lipid oxidation, volatile production, and odor
intensity was evaluated using correlation coecients.
Mean values and standard errors of the mean (SEM)
were reported when necessary.
3. Results and discussion
3.1. Lipid oxidation
Irradiation produced more TBARS than nonirradiated control, but only in aerobic-packaged muscle
strips at day 0. Longissimus dorsi muscle strips stored
for 5 days in aerobic packaging produced higher
TBARS than those of 0-day storage (Table 1). Ahn,
Olson, Lee et al. (1998) reported that irradiation and
high fat content accelerated the lipid oxidation in raw
pork patties during storage. However, oxygen availability during storage was more important than irradiation on the lipid oxidation and volatiles of raw and
cooked meat (Ahn et al., 1998b; Ahn, Olson, Jo, Love &
Jin, 1999).
3.2. Volatiles production of Longissimus dorsi muscle
strips
At Day 0 with vacuum packaging, irradiated muscle
strips produced a few volatiles that were not found in
nonirradiated meat (Table 2). They were thiobismethane, 3-methoxy-1-propene, thioacetic acid methyl
ester, 2,3-dimethyl disul®de, toluene, and 2,3-dimethyl
211
Table 1
TBARS values of irradiated pork Longissimus dorsi muscle strips with
di€erent packaginga±d
Vacuum packaging
IR (kGy)
0 days
5 days
Aerobic packaging
SEM
0 days
5 days
SEM
TBARS value (mg MDA/kg meat)
0
0.42
0.48
0.061
5
0.41
0.60
0.075
10
0.54
0.60
0.022
SEM
0.037
0.072
0.33by
0.52bx
0.50bx
0.038
0.86a
0.93a
1.04a
0.095
0.112
0.047
0.030
a
Samples were analyzed using a ¯uorometric method (n=4).
a,b; Di€erent letters within a row with same packaging are signi®cantly di€erent (p<0.05).
c
x,y; Di€erent letters within a column are signi®cantly di€erent
(p<0.05).
d
Abbreviations: TBARS, 2-thiobarbituric acid reactive substances;
MDA, malonaldehyde.
b
trisul®de. Most of the newly created volatiles were
sulfur compounds, and the amount of 2,3-dimethyl disul®de was the highest, which accounted for approximately 75% of all the total new volatiles produced by
irradiation. We assume that these new volatile compounds are responsible for the irradiation odor and are
originated from proteins by radiolytic reactions of irradiation. However, irradiation-dose e€ect on the production of new radiolytic products was signi®cant only
for 3-methoxy-1-propene, 2,3-dimethyl disul®de, and
toluene. On the other hand, the amount of carbon disul®de, 1-octanol, 3-chloropyridine, piperdine carboxyaldehyde, 2,2,8-trimethyl decane, 2,2,4,6,6-pentamethyl
heptane, 2,6-dimethyl octane, and 2,8-dimethyl undecane in vacuum-packaged muscle strips at day 0 were
decreased by irradiation. The amounts of lipid oxidation products, such as aldehydes, ketones, and alcohols,
were either not in¯uenced or decreased by irradiation.
This indicates that the major contributor of o€-odor in
vacuum-packaged irradiated meat is not lipid oxidation,
but radiolytic breakdown of sulfur-containing amino
acids (Table 2). Champaign and Nawar (1969) found
that hydrocarbons are the major radiolytic products in
fat and are related to the fatty acid composition of the
fat. Merritt, Angelini and Graham (1978) postulated
that carbonyls are formed in irradiated meats due to the
reactions of hydrocarbon radicals with molecular oxygen, which follows the same pathway as normal lipid
oxidation. Hansen, Chen and Shieh (1987) reported that
the amount of octane, 1-octene, hexanal, and nonane in
irradiated chicken increased with the irradiation dose,
but the volatile compounds were not unique products of
irradiation.
At day 0 with aerobic packaging, all the new volatiles,
except for 2,3-dimethyl trisul®de, found in vacuumpackaged irradiated muscle strips also were found in
aerobic-packaged meat (Table 2). The amount of carbon
212
D.U. Ahn et al. / Meat Science 54 (2000) 209±215
Table 2
Production of volatiles in irradiated pork Longissimus dorsi muscle strips after 0 days storagea,b
Vaccum packaging
Aerobic packaging
Volatiles
0 kGy
5 kGy
10 kGy
SEMc
0 kGy
5 kGy
10 kGy
Area (ion counts1000)
Propanol
Dimethyl sul®de
Carbon disul®de
3-Methoxy-1-propene
2-Ethyl-1-propene
Cloroform
1-Octanol
Thioacetic acid methyl ester
2,3- Dimethyl disul®de
Toluene
3-Chloropyridine
3-Ethyl-4-methyl hexane
2,3-Dimethyl trisul®de
Piperdine carboxyaldehyde
2,2,8-Trimethyl decane
2,2,4,6,6-Pentamethyl heptane
3,5-Dimethyl octane
Undecane
2,6-Dimethyl octane
2,5-Dimethyl undecane
2,8-Dimethyl undecane
673
ndbd
457a
ndc
99
131
461a
ndb
ndb
ndc
1225a
241
ndb
534a
317a
142a
940
92
524a
271a
276a
622
216a
19b
132b
94
87
187b
158a
2701a
191b
568b
93
121a
218b
103b
41b
844
52
206b
103b
90b
803
138a
20b
271a
119
72
163b
191a
3044b
321a
492b
138
69ab
265b
188b
77b
908
77
342ab
171ab
167b
92.4
42.2
25.3
29.5
12.1
26.9
63.3
45.1
401.1
14.1
130.9
40.5
28.5
67.0
38.4
16.9
148.2
17.4
66.5
31.7
31.8
557
ndb
241a
ndc
80
62
47
ndb
ndc
ndb
206
169
nd
184
260
106
1077
85
542
275
270
633
61a
65b
96b
100
58
40
53ab
685b
133a
169
214
nd
231
400
170
1274
124
804
421
405
729
95a
44b
175a
86
73
25
122a
1457a
224a
136
298
nd
208
527
223
1592
162
1026
537
516
74.2
11.8
38.5
8.2
16.9
10.4
13.3
25.4
192.9
33.7
53.2
74.8
±
48.4
127.4
59.5
277.4
36.6
221.1
114.3
109.8
6382
6844
8033
792.2
4159
6143
8253
1127.4
Total volatiles
a
b
c
d
SEM
Samples (4-g) were purged immediately after sampling (n=4).
a±c; Di€erent letters within a row with same packaging are signi®cantly di€erent (p<0.05).
SEM, standard error of the mean.
nd, not detected.
disul®de in aerobic-packaged irradiated meat was also
signi®cantly lower than that in vacuum-packaged irradiated meat. However, the amounts and the changes of
volatiles in¯uenced by irradiation were smaller in aerobic packaging than in vacuum packaging. This indicates
that most of these volatiles either newly produced or
in¯uenced by irradiation are highly volatile (Table 2).
After 5 days of storage in vacuum packaging, the
volatile compounds found in muscle strips were very
similar to those at day 0, but the compositions of volatiles in muscle strips were di€erent from those of day 0
(Table 3). The amount of dimethyl sul®de increased
by four to sixfold and propanal by 50%, but that of
octanol was decreased to 40±70%, 3-chloropyridine to
25±50%, 2,3-dimethyl disul®de to 50±70%, piperdine
carboxyaldehyde to 25±30%, and 3,5-dimethyl octane
to 50±60% of the day 0 values over the 5-days storage
period. 1-Butene, not found at day 0, was also found in
muscle strips at day 5. However, these changes in volatiles during the 5-days storage in vacuum packaging
were not of sucient magnitude to in¯uence overall
odor characteristics of the muscle strips (Table 3).
After 5 days of storage in aerobic packaging, the
amount of all volatile components except propanal,
dimethyl sul®de, and carbon disul®de decreased to 25 to
50% of the day 0 values. Many of the new volatile
compounds formed by irradiation disappeared or
reduced to very low levels during the 5-days storage in
aerobic conditions, and the amounts of total volatiles
were also reduced to 50 to 25% of the original levels.
The amounts of total volatiles in aerobic-packaged
muscle strips were less than one-half or one-third of
those found in vacuum packaged meat with the same
irradiation dose (Table 3). Results from Tables 2 and 3
indicate that irradiation has the strongest, packaging
the intermediate, and storage time the lowest e€ect on
the volatile production and composition in raw muscle
strips. Irradiation-induced oxidative chemical changes
are dose dependent, and the presence of oxygen has a
signi®cant e€ect on the development of oxidation and
odor intensity (Huber et al., 1953; Katusin-Razem et al.,
1992; Merritt, Angelini, Wierbicki & Shuts, 1975). Ahn
et al. (1999) reported that irradiated meat produced
more volatiles than found in nonirradiated patties, and
the proportion of volatiles varied by the packagingirradiation conditions of the patties.
With vacuum packaging, only 2,5-dimethyl undecane
had a signi®cant negative correlation with TBARS
of nonirradiated muscle strips. 3-Methoxy-1-propene,
toluene, 3-ethyl-4-methyl hexane, 2,2,8-trimethyl decane,
D.U. Ahn et al. / Meat Science 54 (2000) 209±215
213
Table 3
Production of volatiles in irradiated pork Longissimus dorsi muscle strips after 5-day storage at 4 Ca,b
Vaccum packaging
Aerobic packaging
Volatiles
0 kGy
5 kGy
10 kGy
SEMc
0 kGy
5 kGy
10 kGy
Area (ion counts1000)
1-Butene
Propanol
Dimethyl sul®de
Carbon disul®de
3-Methoxy-1-propene
2-Ethyl-1-butanol
Cloroform
1-Octanol
Thioacetic methyl ester
2,3-Dimethyl disul®de
Toluene
3-Chloropyridine
3-Ethyl-4-methyl hexane
2,3-Dimethyl trisul®de
Piperdine carboxyaldehyde
2,2,8-Trinethyl decane
2,2,4,6,6-Pentamethyl heptane
3,5-Diemthyl octane
Undecane
2,6-Dimethyl undecane
2,5-Dimethyl undecane
2,8-Dimethyl undecane
37c
889
36b
780a
ndbd
88
110
323a
nd
ndb
ndb
608a
68
ndc
148
125
52
562
50
399
271
187
248b
960
1387a
413ab
160a
84
94
77b
87
1947a
113a
203b
74
28b
72
86
36
417
34
249
105
92
358a
1185
554b
233b
214a
153
95
40b
180
1765a
155a
132b
93
59a
68
141
54
606
38
341
197
183
18.1
108.7
172.2
123.6
20.1
19.0
15.8
34.3
55.6
333.3
13.4
75.1
13.6
5.3
20.7
23.7
11.0
75.6
9.3
75.5
58.4
40.2
ndc
601
ndc
248
54b
60
42a
nd
nd
nd
ndb
132
37
nd
42
67
30
386
21
236
126
136
76b
841
76a
134
105a
53
ndb
nd
nd
nd
40a
97
29
nd
39
45
23
260
22
171
85
88
169a
762
38b
91
132a
46
ndb
nd
nd
nd
155a
49
44
nd
28
74
31
348
27
237
111
105
11.4
82.8
9.4
42.8
11.2
8.5
7.1
±
±
±
13.4
23.4
8.7
±
3.8
16.5
4.2
58.7
4.0
52.8
30.2
38.4
Total volatiles
4729
6963
6832
613.5
2217
2182
2351
261.5
a
b
c
d
SEM
Samples (4-g) were purged immediately after sampling (n=4).
a±c; Di€erent letters within a row with the same packaging are signi®cantly di€erent (p<0.05).
SEM, standard error of the mean.
nd, not detected.
2,2,4,6,6-pentamethyl heptane, 2,5-dimethyl undecane,
and 2,8-dimethyl undecane were positively correlated
with TBARS of irradiated muscle strips (Table 4).
However, the reasons why these speci®c branched
hydrocarbons were signi®cantly correlated to TBARS
of vacuum packaged meat are not understood. With
aerobic packaging, 3-methoxy-1-propene, 1-octanal,
and piperdine carboxyaldehyde had signi®cant correlations with TBARS of nonirradiated muscle strips.
However, none of the volatiles produced in irradiated
muscle strips had signi®cant correlations with TBARS
(Table 4). This indicates that volatiles produced in
aerobic-packaged nonirradiated meat are related to lipid
oxidation, but most of the volatiles produced by irradiation are not related to lipid oxidation. Apparently, the
majority of the branched hydrocarbons listed in Tables
2 and 3 should be originated from lipids and sulfurcontaining compounds from amino acids. Therefore,
the compositions of fatty acid and amino acid in meat
should have signi®cant e€ect on the pro®les of the
volatiles. However, the contribution of lipids and protein (amino acids) interactions on the production of new
volatiles during irradiation and subsequent storage
should not be overlooked. It is dicult to draw any
conclusion on the mechanisms of o€-odor production in
irradiated meat with current study.
In vacuum packaging, irradiated Longissimus dorsi
muscle strips produced signi®cantly stronger irradiation
odor than found in nonirradiated, but no irradiation
dose or storage e€ect was found (Table 5). Many of the
sensory panels characterized irradiation odor as barbecued corn-like odor, but some described it as burnt,
bloody, sweet, old, sulfur, or pungent. Many sensory
panels were used to barbecued corn-like odor and
showed little objection to the irradiation odor. As in
vacuum packaging, irradiation produced a signi®cant
irradiation odor in aerobic-packaged muscle strips.
Irradiation of muscle strips at 10 kGy produced stronger irradiation odor than that at 5 kGy, and 5-day storage reduced the intensity of irradiation odor in muscle
strips, but the reduction was signi®cant in samples irradiated at 5 kGy. Irradiation had no negative e€ect on
the acceptance of meat under all packaging and storage
conditions (Table 5).
Huber et al. (1953) reported that meat sterilized
through irradiation developed a characteristic odor,
which has variously been described as ``metallic,'' ``sul®de,'' ``wet dog,'' ``wet grain,'' or ``burnt''. Batzer and
214
D.U. Ahn et al. / Meat Science 54 (2000) 209±215
Table 4
Correlation coecients between the amount of volatile compounds and TBARS of irradiated and nonirradiated pork Longissimus dorsi muscle
stripsa
Vacuum packaging
Aerobic packaging
Volatiles
Nonirradiated
Irradiated
Nonirradiated
Irradiated
1-Butene
Propanol
Dimethyl sul®de
Carbon disul®de
3-Methoxy-1-propene
2-Ethyl-1-butanol
Cloroform
1-Octanol
Thioacetic acid methyl ester
2,3-Dimethyl disul®de
Toluene
3-Chloropyridine
3-Ethyl-1-methyl hexane
2,3-Dimethyl trisul®de
Piperdine carboxyaldehyde
2,2,8-Trimethyl decane
2,2,4,6,6-Pentamethyl heptane
3,5-Dimethyl octane
Undecane
2,6-Dimethyl octane
2,5-Dimethyl undecane
2,8-Dimethyl undecane
ÿ0.24
ÿ0.43
ÿ0.37
ÿ0.50
±
ÿ0.26
0.04
0.32
±
±
±
0.33
0.17
±
0.35
ÿ0.03
ÿ0.04
ÿ0.19
ÿ0.18
ÿ0.50
ÿ0.81*
ÿ0.55
ÿ0.13
ÿ0.06
ÿ0.48
ÿ0.46
0.53*
0.28
ÿ0.21
0.37
ÿ0.15
0.12
0.52*
0.33
0.57*
ÿ0.02
0.38
0.64**
0.62*
0.42
0.38
0.40
0.58*
0.61*
±
ÿ0.31
±
0.30
ÿ0.74*
0.11
0.56
0.90**
±
±
±
0.61
0.68
±
0.79*
0.59
0.49
0.68
0.59
0.49
0.43
0.32
0.32
ÿ0.28
ÿ0.41
ÿ0.17
0.39
ÿ0.44
ÿ0.10
ÿ0.20
0.09
0.03
ÿ0.10
ÿ0.27
ÿ0.23
±
ÿ0.35
ÿ0.23
ÿ0.25
ÿ0.23
ÿ0.25
ÿ0.23
ÿ0.23
ÿ0.23
Total volatiles
ÿ0.19
0.25
0.60
ÿ0.21
a
n=8 for nonirradiated and n=16 for irradiated.
Table 5
Sensory characteristics of irradiated pork Longissimus dorsi muscle
strips refrigerated for 5 daysa±c
Vacuum packaging
Irradiation
0 days
5 days
Aerobic packaging
SEM
0 days
5 days
SEM
Irradiation odor intensityd
0 kGy
3.49y
3.27y
5 kGy
9.90x
8.40x
10 kGy
10.49x
8.94x
SEM
0.730
0.768
0.808
0.804
0.670
5.09y
8.19ax
9.27x
0.858
3.10z
5.26by
7.72x
0.652
0.966
0.769
0.577
Acceptance of meat donore
0 kGy
7.40
5.63
5 kGy
6.11
4.68
10 kGy
6.15
3.74
SEM
1.039
0.864
0.889
1.000
1.049
5.07
5.40
6.22
1.055
6.61
5.10
6.30
0.841
0.884
0.916
1.154
a
Pork strip (5-g) was put in a sample vial (20-ml), capped, and
stored at 4 C until analyzed. Thirteen trained sensory panels were used.
b
a,b; Di€erent letters within a row with the same packaging are
signi®cantly di€erent (p<0.05).
c
x±z; Di€erent letters within a column are signi®cantly di€erent
(p<0.05).
d
Irradiation odor intensity: 0, no irradiation odor; 15, very strong
irradiation odor.
e
Acceptance of meat odor: 0, not acceptable; 15, highly acceptable.
Doty (1955) found that methyl mercaptan and hydrogen sul®de were important to irradiation odor, and the
precursors of the undesirable odor compounds in irradiated meat were sulfur-containing compounds that
were water soluble. GC separation and odor evaluation
of volatiles indicated that hydrocarbons have very high
odor thresholds. However, most sulfur and carbonyl
compounds had low odor thresholds and were considered as important to irradiation odor (Angelini,
Merritt, Mendelshon & King, 1975; Wick, Murray,
Mitzutani & Koshika, 1967). These results indicate that
sulfur-containing compounds could be the major volatile components responsible for irradiation odor in
meat. Patterson and Stevenson (1995) found that dimethyl trisul®de is the most potent o€-odor compound,
followed by cis-3- and trans-6-nonenals, oct-1-en-3-one,
and bis(methylthio-)methane in irradiated chicken meat.
These studies also provided evidence to support the
concept that the changes that occur following irradiation are distinctly di€erent from those of warmed-over
¯avor in oxidized meat.
4. Conclusion
Sulfur-containing volatiles, not lipid oxidationdependent volatiles, were responsible for the o€-odor in
irradiated pork. Irradiation-dependent production of
sulfur compounds was not dose-dependent at <10 kGy
level, but was related to radiolytic degradation of amino
acids. Studies are needed to determine the interactions
of sulfur-containing and other volatile compounds from
D.U. Ahn et al. / Meat Science 54 (2000) 209±215
amino acids and lipid groups, and the lowest irradiation
dose level that produces sulfur compounds in meat.
Irradiation produced irradiation odor but the odor was
found to be acceptable. The sensory characteristics of
irradiated meat were characterized as barbecued cornlike odor, and sensory panels showed no objection to
the odor. We assume that this would be true for the
majority of US customers, but more detailed sensory
studies are required to con®rm it.
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