Meat Science 56 (2000) 387±395
www.elsevier.com/locate/meatsci
In¯uence of dietary conjugated linoleic acid on volatile pro®les,
color and lipid oxidation of irradiated raw chicken meat
M. Du, D.U. Ahn *, K.C. Nam, J.L. Sell
Department of Animal Science, Iowa State University, Ames, IA 50011-3150, USA
Abstract
Forty-eight, 27-week-old White Leghorn hens were fed a diet containing 0, 1.25, 2.5 or 5.0% conjugated linoleic acid (CLA) for
12 weeks. At the end of the 12-week feeding trial, hens were slaughtered, and boneless, skinless breast and leg meats were separated
from carcasses. Meats were ground through 9 and 3-mm plates, and patties were prepared. Patties prepared from each dietary
treatment were divided into two groups and either vacuum- or aerobic-packaged. Patties were irradiated at 0 or 3.0 kGy using a
linear accelerator and stored at 4 C. Samples were analyzed for thiobarbituric acid reactive substances, volatile pro®les, color and
odor characteristics at 0 and 7 days of storage. Dietary CLA reduced the degree of lipid oxidation in raw chicken meat during
storage. The content of hexanal and pentanal in raw chicken meat signi®cantly decreased as dietary CLA level increased. Irradiation accelerated lipid oxidation in meat with aerobic packaging, but irradiation e€ect was not as signi®cant as that of the packaging.
Dietary CLA treatment improved the color stability of chicken patties. Color a*-value of irradiated raw chicken meat was higher
than that of the nonirradiated meat. Dietary CLA decreased the content of polyunsaturated fatty acid and increased CLA in
chicken muscles, which improved lipid and color stability and reduced volatile production in irradiated and nonirradiated raw
chicken meat during storage. # 2000 Elsevier Science Ltd. All rights reserved.
Keywords: Conjugated linoleic acid; Volatiles; Color; Raw chicken meat; Lipid oxidation; O€-odor
1. Introduction
Dietary conjugated linoleic acid (CLA) has been
shown to have bene®cial e€ects on human health (Belury, Nickel, Bird & Wu, 1996; Ip, Scimeca & Thompson, 1995). CLA can be incorporated into meat, milk
and egg by supplementing CLA sources in animal diets.
CLA sources are prepared by alkali isomerization of
linoleic acid-rich plant oils, and are available as free
acid forms. Ip et al. (1999) indicated that CLA in butter
from CLA-fed cows (triglyceride form) had higher tissue retention rates and had better anticancer e€ect than
the equal amount of CLA sources (free acid forms) did
in rats. However, dietary CLA may a€ect the sensory
characteristics of meat, milk or egg. Loor and Herbein
(1998) reported that CLA-fed cows produced milk with
far less fat than controls. Ahn, Sell, Jo, Chamruspollert
and Je€ery, (1999) found that hard-boiled eggs from
* Corresponding author. Tel.: +1-515-294-6595; fax: +1-515-2949143.
E-mail address: duahn@iastate.edu (D.U. Ahn).
hens fed CLA-enriched diet were rubbery and elastic,
and were dicult to break using an Instron. In pork,
CLA feeding improved the marbling of loin and
reduced overall fat content (Dugan, Aalhus, Jeremiah,
Kramer & Schaefer, 1999). However, the in¯uence of
dietary CLA on the volatiles, color and odor characteristics of meat has not been studied.
Irradiation treatment is the best method to control
bacterial load in raw meat (Farkas, 1998). However,
ionizing radiation generates free radicals that may
induce lipid peroxidation and other chemical changes,
and in¯uence the quality of foods (Branka, Branka &
Dusan, 1992; Wong, Herald & Hachmeister, 1995).
Poultry meat contains more polyunsaturated fatty acids
(PUFA) than red meat and can be more susceptible to
oxidative changes by irradiation. Dietary CLA is
reported to reduce the content of PUFA in meat (Du,
Ahn & Sell, 1999; Meynier, Genot & Gandemer, 1999).
Therefore, meats from animals fed CLA will be less
susceptible to lipid oxidation, color changes and volatile
production than those from a control diet. Meat odor
and color after irradiation are critical factor that can
0309-1740/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved.
PII: S0309-1740(00)00067-X
388
M. Du et al. / Meat Science 56 (2000) 387±395
in¯uence consumer acceptance of the meat. The objective of this study was to determine the in¯uence of dietary CLA on lipid and color stability, volatile production
and odor characteristics of raw chicken meat with different irradiation and packaging conditions.
2. Materials and methods
2.1. Sample preparation
Forty-eight, 27-week-old White Leghorn hens kept in
individual cages were assigned to one of the four diets
containing 0, 1.25, 2.5 or 5% CLA source containing
about 62% CLA isomers (Conlinco, Inc. Detroit Lakes,
MN). The energy level was maintained by substituting
the CLA source with soybean oil on a weight:weight
basis (Du, et al., 1999). After 12 weeks of feeding with
experimental diets, hens were sacri®ced, and breast and
leg muscles were separated, vacuum-packaged and
stored at ÿ20 C for 6 months. Meats of three birds
from a dietary treatment were pooled and ground together through 9 and 3-mm plates, and used as a replication. Patties (40 g) prepared from each dietary
treatment were divided into two groups and either
vacuum- or aerobic-packaged. Patties were irradiated at
0 or 3.0 kGy using a linear accelerator. Samples were
analyzed for thiobarbituric acid reactive substances
(TBARS) and volatile pro®le at 0 and 7 days of storage
at 4 C. Odor characteristics and color were analyzed at
7 days of storage.
2.2. Separation of lipid classes and fatty acid
composition analysis
Lipid separation and composition analyses were done
as described in Du et al. (1999). Brie¯y, 2 g of meat
patties was weighed into a test tube with 20 ml solvent
(chloroform: methanol=2:1, vol.vol.) and homogenized. Twenty-®ve mg of butylated hydroxyanisole
(BHA, 10%) dissolved in 98% ethanol was added to
sample prior to homogenization. The homogenate was
®ltered into a 100-ml graduated cylinder and 5 ml of
0.88% NaCl solution was added. Then, the ®ltrate was
mixed well. The contents were stored until the aqueous
and organic layers clearly separated. The lower layer
was dried at 50 C under nitrogen.
One ml of methylating reagent (anhydrous methanolic-HCl-3N, Supelco, Bellefonte, PA) was added into
extracted lipid and incubated in a water bath at 60 C
for 40 min. Two ml of hexane was added to extract
methylated fatty acids. The top hexane layer containing
methylated fatty acids was used for gas chromatography±mass spectrometry (GC±MS) analysis. GC±MS
conditions were the same as described in Du et al.
(1999).
2.3. Volatile analysis
A purge-and-trap apparatus connected to a gas
chromatograph (GC) was used to analyze the volatiles
from meat patties. Precept II and Purge-and-Trap
Concentrator 3000 (Tekmer-Dohrman, Cincinnati,
OH) were used to purge and collect volatiles. Two g of
raw meat were placed in a sample vial (40 ml) and then
added in one pack of oxygen absorber (Ageless Type
Z-100, Mitsubishi Gas Chemical America, Inc., New
York). The vials were ¯ushed with helium gas
(99.999%) for 5 s at 40 psi and capped tightly with a
Te¯on-lined, open-mouth cap. Vials were placed in a
refrigerated (4 C) sample-tray. The maximum sample
holding time in the sample tray before volatile analysis
was less than 10 h to minimize oxidative changes during the sample holding time (Ahn, Jo & Olson, 1999b,
1999c). Meat samples were purged with helium gas (40
ml/min) for 15 min, and volatiles were trapped at 20 C
using a Tenax/silica gel/charcoal column (TekmarDorham) and desorbed for 2 min at 220 C. The desorbed volatiles were concentrated at ÿ100 C using a
cryofocusing unit before being thermally desorbed
(220 C) and injected (30 s) into a capillary GC column.
Ramped oven temperature was used. The initial oven
temperature was 0 C and was held for 1.5 min. After
that the oven temperature was increased to 20 C at
4 C per min, increased to 80 C at 10 C per min,
increased to 180 C at 20 C per min and then kept for
4.50 min. The column used was an HP-Wax (7.5 m)
and HP-5 (30 m, Hewlett-Packard Co.) combined column, and the ¯ow pressure was set at 12 psi. A mass
selective detector (MSD, HP 5973, Hewlett-Packard
Co.) was used to determine volatile components. The
ionization potential of the MS was 70 eV, and scan
range was 33.1±450. Identi®cation of volatiles was
achieved by comparing mass spectral data of samples
with those of the Wiley library (Hewlett-Packard Co.)
and also the standards. The area of each peak was
integrated by using ChemStation software (HewlettPackard Co.), and total ion counts104 was reported
as an indicator of volatiles generated from meat
samples.
2.4. TBARS analysis
Three g of meat was weighed into a 50-ml test tube
and homogenized with 15 ml of deionized distilled water
using a Polytron homogenizer (Type PT 10/35, Brinkman Instruments, Inc., Westbury, NY) for 10 s at highest speed. One ml of the meat homogenate was
transferred to a disposable test tube (3100 mm), and
butylated hydroxyanisole (50 ml, 7.2%) and thiobarbituric acid/trichloroacetic acid (TBA/TCA) (2 ml) were
added. The mixture was vortexed and then incubated in
a boiling water bath for 15 min to develop color. The
M. Du et al. / Meat Science 56 (2000) 387±395
sample was then cooled in cold water for 10 min, vortexed again and centrifuged for 15 min at 2000 g. The
absorbance of the resulting supernatant solution was
determined at 531 nm against a blank containing 1 ml of
deionized distilled water and 2 ml of TBA/TCA solution. The amounts of TBARS were determined by
comparing the standard curve of absorbance at 531 nm
for series of malondialdehyde solutions analyzed by the
same method, and expressed as milligrams of malondialdehyde per kilogram of meat (Ahn, Olson, Lee,
Jo, Chen & Wu, 1998).
2.5. Color measurement
The color of meat patties was measured in package
using a Hunter LabScan Colorimeter (Hunter Laboratory, Inc., Reston, VA) and expressed as color L (lightness), a* (redness) and b* (yellowness) values. The same
package materials were used to cover a white standard
plate in order to eliminate the in¯uence of packaging
materials on meat color.
2.6. Sensory analysis
The intensity and descriptive characteristics of odor
of raw chicken meat were determined using a 16-member trained sensory panel. 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.
Four sample sets using packaging and irradiation combinations (vacuum-packaged/nonirradiated, aerobicpackaged/nonirradiated, vacuum-packaged/irradiated
and aerobic-packaged/irradiated) were prepared. Two
sets of samples were presented to sensory panelists with
a 30-min interval. For evaluation of odor, samples in
coded, capped scintillation vials (glass) were presented
to each panelist in isolated booths. A 15-cm linear horizontal scale, anchored with the words `no o€-odor' and
`very strong o€-odor' at opposite ends, was used to rate
the samples on the intensity of o€-odor. The responses
from the panelists were expressed in numerical values
ranging from 0 (no o€-odor) to 15 (strong o€-odor) to
the nearest 0.5 cm. Sensory panelists were also asked to
characterize the odor that best described it.
3. Results and discussion
3.1. TBARS values
The basic chemical composition indicated that there
were no di€erences in total fat and water content, and
pH values in raw chicken meat from hens fed di€erent
dietary CLA. The fatty acid composition analysis,
however, showed that dietary CLA reduced the content
of monounsaturated fatty acids and non-CLA PUFA,
but increased saturated fatty acids content in chicken
meat. Increasing amounts of linoleic acid in raw chicken
meat were replaced by CLA as dietary levels of CLA
increased (Table 1).
TBARS results at day 0 indicated that meats from
hens fed CLA had lower TBARS than controls under
all packaging and irradiation conditions (Table 2). As
dietary CLA levels increased, TBARS in both irradiated
and nonirradiated meat decreased, and maximum
decrease of TBARS value was observed at 5.0% dietary
CLA treatment. The increased storage stability in meats
from hens fed CLA should be caused by the increase in
saturated fatty acid (SAFA) and decreased non-CLA
PUFA in meat. Although CLA itself did not act as an
antioxidant, its conjugated structure made the fatty acid
less susceptible to free radical attacks. Irradiation and
packaging also had signi®cant in¯uence on the TBARS
values (Table 2). Signi®cant interaction between diet
and irradiation, and diet and packaging indicated that
dietary CLA improved the stability of meat lipids during irradiation and storage under aerobic conditions.
After 7 days of storage, the TBARS values of aerobicpackaged raw chicken meat were much higher than that
of the 0 day, indicating signi®cant development of lipid
oxidation in those meats during the storage. The
TBARS values of meat from hens fed CLA produced
less TBARS than the control, and a 2.5% or higher level
of CLA treatment was better than 1.25% in reducing
lipid oxidation in aerobic-packaged chicken meat
Table 1
Fatty acid composition of chicken meat patties prepared from laying
hens fed di€erent levels of CLAa
Fatty acid composition Level of CLA (% of total fatty acids)
2.7. Statistical analysis
The e€ect of dietary CLA on the volatiles, TBARS
and sensory data of cooked meat was analyzed statistically by GLM using SAS1 software (SAS Institute,
1985). Student±Newman±Keuls multiple range test was
used to compare di€erences among mean values
(P<0.05). Mean values and SEM were reported. Tukey
grouping analysis was employed to analyze the possibilities of diet, irradiation and packaging e€ects.
389
Linoleic acid
Arachidonic acid
Total CLA
Total SAFA
Total MUFA
Total PUFA
Total non-CLA PUFA
Control
1.25%
CLA
2.5%
CLA
5.0%
CLA
SEM
26.3a
5.6a
0.0d
31.7a
34.3a
33.8
33.8a
24.8a
4.2b
3.8c
32.8b
30.8b
33.9
30.1b
20.6b
4.0b
7.2b
36.4c
27.7c
32.8
25.6c
14.6c
2.6c
13.9a
39.3c
24.7d
33.1
19.2d
0.87
0.23
0.26
0.73
0.51
0.53
0.32
a
Means within a row with no common letter di€er signi®cantly
(p<0.05); n=4.
390
M. Du et al. / Meat Science 56 (2000) 387±395
lower aldehyde contents in meats from hens fed CLA
diets than the control could be related to the decrease in
non-CLA n-6 fatty acids (linoleic and arachidonic acids)
in those meats (Table 1). The contents of hexanal and
pentanal detected in this study showed that they were
positively related to linoleic acid but negatively related
to CLA content in meat (Table 1). This indicated that
CLA in meat did not participate in lipid oxidation and
suggested that CLA was not susceptible to oxidative
change. N-6 PUFA, such as linoleic acid and arachidonic acid, are suggested to be the precursors for hexanal (Meynier et al., 1999). With vacuum packaging, the
content of 2-propanone in both irradiated and nonirradiated raw meat from 5% dietary CLA treatment
was higher, but that of the hexanal was lower than other
dietary treatments (Table 3). The reason for the
increased 2-propanone and decreased hexanal levels in
raw meat from high dietary CLA (5%) was not clear,
but should not be related to lipid oxidation in the meat,
especially with vacuum packaging.
After 7 days of storage, the amount of total volatiles
in aerobic-packaged raw chicken meat increased from 0
during storage. However, irradiation had no signi®cant
e€ect on the oxidation of raw chicken meat during the
7-day storage (Table 2). No increase in TBARS was
observed in raw chicken meat with vacuum packaging.
3.2. Volatile pro®les
At day 0 with aerobic packaging, nonirradiated raw
meat from hens fed CLA produced signi®cantly lower
amounts of acetaldehyde, propanal, pentanal, hexanal
and total volatiles than the control. The content of 2propanone in meat from hens fed 5% CLA was higher
than that of the other dietary treatments (Table 3).
Volatile pro®les and the e€ect of CLA on the content of
aldehydes, 2-propanone and total volatiles in irradiated
raw chicken meat also had similar trends as in aerobicpackaged. However, the content of hexanal in irradiated
raw chicken meat was several folds higher than that of
the nonirradiated meat, and dietary CLA signi®cantly
reduced it (Table 3). The amounts of aldehydes and
total volatiles in both irradiated and nonirradiated meat
were in good agreement with TBARS (Table 2). The
Table 2
TBARS values (mg/kg) of raw chicken patties after 0 and 7 days of storagea
Nonirradiated
Diet
Aerobic
packaging
Day 0
Control
1.25% CLA
2.5% CLA
5.0% CLA
S.E.M.
Irradiated
Vacuum
packaging
2.88a
1.58b
1.22c
0.73d
0.04
1.07a
0.68b
0.56c
0.52c
0.04
3.61a
1.61b
1.46b
0.77c
0.15
1.28a
0.86b
0.72c
0.56d
0.03
10.55a
7.46b
4.50c
4.20c
0.26
1.22a
0.90b
0.74b
0.56c
0.05
Probability
0.0001
0.0002
0.0001
0.004
0.0001
0.0001
0.04
9.39a
7.21b
6.29b
3.45c
0.304
0.65a
0.58b
0.54b
0.47c
0.02
Diet (D)
Irradiation (IR)
Packaging (P)
DIR
DP
IRP
DIRP
a
Vacuum
packaging
(TBARS values (mg/kg))
Diet (D)
Irradiation (IR)
Packaging (P)
DIR
DP
IRP
DIRP
Day 7
Control
1.25% CLA
2.5% CLA
5.0% CLA
S.E.M.
Aerobic
packaging
Means within a row with no common letters di€er signi®cantly (p<0.05); n=4.
Probability
0.0001
0.06
0.0001
0.0001
0.0001
0.3
0.0001
M. Du et al. / Meat Science 56 (2000) 387±395
391
Table 3
Volatile pro®les of nonirradiated and irradiated raw chicken patties after 0 day of storagea
Volatile compounds
Aerobic packaging (total ion counts104)
Vacuum packaging (total ion counts104)
Control
1.25%
2.5%
5.0%
S.E.M.
Non irritated
Acetaldehyde
1-Heptene
Propanal
Octane
2-Propanone
1-Octene
Pentanal
Hexanal
Butanol
1-Penten-3-ol
Total volatiles
49a
34
133a
36
559b
0
304a
3708a
17
8a
4848a
19b
14
42b
28
791b
0
213ab
1391b
16
4b
2518b
13b
17
28b
48
656b
0
119ab
1614b
12
5ab
2512b
13b
10
16b
34
1112a
0
73b
786b
12
6ab
2062b
Irradiated at 3.0 kGy
Acetaldehyde
1-Heptene
Propanal
Octane
2-Propanone
1-Octene
Pentanal
Hexanal
Butanol
1-Penten-3-ol
Total volatiles
186a
37
63a
53
770b
24
343a
4029a
26
15
5546a
119b
27
30b
50
988ab
26
256ab
2663b
19
7
4185b
122b
23
25b
65
955ab
38
188b
1301c
14
6
2737c
103b
18
18b
55
1351a
16
158b
552d
17
6
2294c
a
Control
1.25%
2.5%
5.0%
S.E.M.
7.7
10.5
17.8
5.6
90.2
0.0
49.1
442
2.9
0.9
346.0
4
0
0
0
732b
21
0
29
7
0
793b
3
0
0
0
613b
20
0
18
9
0
663b
4
0
0
0
645b
17
0
17
6
0
689b
5
0
0
0
1047a
20
0
28
11
0
1111a
1.0
0.0
0.0
0.0
68.2
2.1
0.0
4.4
1.9
0.0
73.7
14.5
11.3
18.4
7.9
138
7.4
40.6
233
2.8
2.8
469.9
11
19
0
0
900b
31
27
505a
7
0
1500
13
16
0
0
1041b
28
33
131b
7
0
1269
13
17
0
0
889b
26
25
98b
10
0
1078
13
14
0
0
1269a
23
24
72b
12
0
1427
2.4
4.9
0.0
0.0
66.9
4.7
4.3
36.7
1.4
0.0
101.7
Means within a row with no common letter di€er signi®cantly (p<0.05); n=4.
day by ®ve- to six-fold. Among the volatiles, the
increases of propanal, pentanal and hexanal were the
most signi®cant in both irradiated and nonirradiated
raw chicken meats (Table 4). A few other aldehydes
such as butanal, 3-methyl butanal, heptanal and octanal, not found in raw chicken meat at day 0, also were
detected. The amounts of aldehydes in chicken meats
from hens fed CLA were lower than the control, but the
proportional increase of aldehydes in CLA meat during
the 7-day storage was higher than the control. This
indicated that CLA itself has no antioxidant e€ect in
meat. This is in agreement with Van den Berg, Cook
and Tribble (1995), who reported that CLA was not an
ecient radical scavenger and had no protective e€ects
on lipid oxidation. CLA is a mixture of linoleic acid
isomers, but CLA is much more stable to oxidative
changes than linoleic acid because of the conjugated
arrangement of double bonds in CLA. Hexanal and
pentanal contents in volatiles were suggested to be good
indicators of oxidation ( Ahn et al., 1998; Liu, Booren,
Gray & Crackel, 1992; Shahidi & Pegg, 1994). In this
study, we also found that there were positive relationships between aldehydes and TBARS values. Aldehydes
composed over 90% of total volatiles in both irradiated
and nonirradiated raw chicken meat after 7 days of
storage, indicating severe lipid oxidation under aerobic
conditions. With vacuum packaging, however, there
was not much change in volatiles content in both irradiated and nonirradiated raw chicken meats during the
7-day storage (Table 4). Thus, raw meats were stable
under vacuum regardless of irradiation conditions. Production of aldehydes in raw meat was strongly in¯uenced by packaging, but diet and irradiation had only
limited impact on those volatiles (Table 5). The irradiation e€ect on the volatiles indicated that 3 kGy irradiation had no in¯uence on the volatile composition of raw
chicken meat after 7 days of storage. Packaging had
signi®cant e€ects on almost all volatiles in raw chicken
meat, showing the importance of oxygen exclusion in
minimizing oxidative changes of meat (Tables 4 and 5).
3.3. Color change
Dietary CLA treatment in¯uenced meat color (Table
6). After 7 days of storage, meat from hens fed a 5.0%
CLA diet had lower L- and b*values, and higher a*
than the control. Visually, the color of meat from the
control diet appeared a little lighter and grayer than
that of the 5.0% CLA diet. This indicated that CLA
improved meat color after 7 days of storage, which may
be related to the improved oxidative stability of meat
from CLA feeding groups. Packaging and irradiation
had signi®cant e€ects on all L, a* and b* values (Table
6). Irradiation increased the a* value of raw chicken
392
M. Du et al. / Meat Science 56 (2000) 387±395
Table 4
Volatile pro®les of nonirradiated and irradiated raw chicken patties after 7 days of storagea
Aerobic packaging (total ion counts104)
Vacuum packaging (total ion counts104)
Volatile compounds
Control
1.25%
2.5%
5.0%
S.E.M.
Nonirradiated
Acetaldehyde
1-Heptene
Propanal
Octane
2-Propanone
1-Octene
Butanal
2-Butanone
3-Methylbutanal
Pentanal
2-Methylpentanal
Hexanal
Heptanal
1-Penten-3-ol
Octanal
Hexanol
Total volatiles
142a
27
975a
133a
992a
15
147
162a
50a
2168a
267a
21 774a
102
335a
43
39
27 371a
81ab
35
640ab
80b
896ab
9
142
130ab
27b
1784ab
177ab
14 485b
136
207b
33
48
18 910b
34b
46
248b
53b
438b
10
51
81c
20b
500c
46b
14 947d
59
67c
19
25
16 644bc
91ab
30
173b
57b
871ab
15
92
104bc
19b
1110bc
34b
8789c
97
54c
28
21
11 566c
21.0
6.3
178
8.7
130
3.4
24.8
12.0
4.4
247
41.6
1166
19.3
24.6
9.4
6.8
1636
21
18
0
30
438
31
0
25
0
0
0
34
0
0
0
5
602
Irradiated at 3.0 kGy
Acetaldehyde
1-Heptene
Propanal
Octane
2-Propanone
1-Octene
Butanal
2-Butanone
3-Methylbutanal
Pentanal
2-Methylpentanal
Hexanal
Heptanal
1-Penten-3-ol
Octanal
Hexanol
Total volatiles
390
39
1645a
186
1241
30
122
148
114
1630
214a
23 397a
364
245a
45a
26
29 836a
235
28
764b
101
1253
22
150
152
58
1694
145ab
12 464b
138
142b
28ab
18
17 391b
196
42
753b
138
1123
19
158
160
96
2119
87ab
13 547b
164
110b
22ab
19
18 753b
147
48
122c
102
1216
16
152
118
65
1683
56b
9143b
164
47b
14b
18
13 111b
60.4
18.7
135
0.6
174.2
3.4
33.2
26.1
26.0
378
35.6
1800
130
29.8
6.6
5.4
2402
9
19
0
36
477
10
0
50
27
126a
0
78
0
0
0
9a
841
a
Control
1.25%
2.5%
5.0%
S.E.M.
8
27
0
32
611
22
0
25
0
0
0
27
0
0
0
10
762
11
34
0
32
581
25
0
23
0
0
0
13
0
0
0
9
728
7
28
0
26
629
29
0
22
0
0
0
18
0
0
0
8
767
3.3
11.8
0.0
7.1
71.8
7.4
0.0
3.0
0.0
0.0
0.0
7.7
0.0
0.0
0.0
1.5
92.0
11
26
0
48
497
19
0
36
18
100a
0
32
0
0
0
8ab
795
11
35
0
37
541
22
0
47
15
37b
0
36
0
0
0
6ab
787
13
31
0
34
720
10
0
52
15
19b
0
22
0
0
0
4b
920
2.1
7.7
0.0
6.0
71.6
5.3
0.0
12.0
3.4
16.2
0.0
13.6
0.0
0.0
0.0
0.9
100.9
Means within a row with no common letter di€er signi®cantly (p<0.05); n=4.
meat, and irradiated meat appeared redder than the
nonirradiated. This result agrees with that of Nanke,
Sebranek and Olson (1998). Large di€erences in all L-,
a*- and b* values between vacuum- and aerobic-packaging indicated that vacuum packaging was helpful in
preserving meat color. Luchsinger et al. (1996) reported
that irradiated vacuum-packaged pork chops appeared
redder and were more stable during storage.
3.4. Sensory analysis
No di€erence in o€-odor among raw chicken meats
from di€erent CLA diets and between packaging within
an irradiation treatment was found (Table 7). However,
irradiation had a signi®cant e€ect on the o€-odor of
raw chicken meat (P<0.0001) after 7 days of storage.
Approximately two-fold higher o€-odor scores in
vacuum-packaged irradiated raw chicken meat compared with nonirradiated meat indicated that the di€erence in o€-odor between irradiated and nonirradiated
meat is not oxidation-related. Heath et al. (1990) and
Hashim, Resurreccion and McWatters (1995) showed
that irradiating raw chicken meat produced a characteristic bloody and sweet aroma. Ahn, Jo and Olson
(1999a) reported that sulfur-containing volatiles, not
lipid oxidation-dependent volatiles, were responsible for
the o€-odor in irradiated pork. Irradiation-dependent
production of sulfur compounds was not dose-dependent at <10 kGy, but was related to radiolytic degradation of amino acids. Batzer and Doty (1955) found
that methyl mercaptan and hydrogen sul®de were important to irradiation odor. Angelini, Merritt, Mendelshon
M. Du et al. / Meat Science 56 (2000) 387±395
393
occur following irradiation are distinctly di€erent from
those of warmed-over ¯avor in oxidized meat. These
results indicated that sulfur-containing compounds
could be the major volatile components responsible for
irradiation odor in meat. Our recent tests with di€erent
column combinations, which detected large amounts of
sulfur-containing compounds in irradiated meats supported this concept (unpublished data). However, no
and King (1975) reported that most sulfur compounds
had low odor thresholds and were considered as important to irradiation odor. 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
Table 5
The probabilities of diet, irradiation and package e€ects on the volatile composition of raw meat patties after 7 days of storagea
Probability
Volatiles
Diet
Irradiation
Packaging
Acetaldehyde
1-Heptene
Propanal
Octane
2-Propanone
Octene
Butanal
2-Butanone
3-Methylbutanal
Pentanal
2-Methylpentanal
Hexanal
Heptanal
1-Penten-3-ol
Octanal
Hexanol
0.004
0.4
0.0001
0.0001
0.2
0.7
0.5
0.2
0.07
0.2
0.0001
0.0001
0.6
0.0001
0.02
0.04
0.0001
0.6
0.007
0.0001
0.002
0.6
0.08
0.004
0.0001
0.04
0.98
0.05
0.1
0.1
0.5
0.002
0.0001
0.1
0.0001
0.0001
0.0001
0.1
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
0.0001
Total volatiles
0.0001
0.1
0.0001
a
Probabilities less than 0.05 were considered as signi®cantly di€erent (n=8).
Table 6
Color values of raw chicken patties after 7 days of storagea
Diet
Nonirradiated
Irradiated
Aerobic packaging
Control
1.25%
2.5%
5.0%
S.E.M.
Vacuum packaging
Aerobic packaging
L
a*
b*
L
a*
b*
L
a*
b*
L
a*
b*
58.5a
56.6b
55.6b
53.2c
0.65
12.9ab
13.3a
12.3b
13.6a
0.23
23.0a
23.0a
20.9b
21.7ab
0.40
53.6a
51.0b
50.1b
49.8b
0.69
18.3
18.9
18.4
17.9
0.28
17.6a
16.8a
15.9b
14.9c
0.30
58.8
57.2
56.3
56.6
0.73
13.8
14.1
14.3
13.6
0.37
22.7a
22.1ab
21.5b
20.1c
0.33
53.7
52.7
51.7
53.6
0.65
20.1
20.2
20.0
19.1
0.36
18.1
17.7
17.0
17.6
0.27
Probability
Treatment
L
a*
b*
Diet (D)
Irradiation (IR)
Packaging (P)
DIR
DP
IRP
DIRP
0.0001
0.0001
0.0001
0.004
0.0003
0.4
0.9
0.1
0.0001
0.0001
0.03
0.08
0.06
0.3
0.0001
0.03
0.0001
0.2
0.2
0.0001
0.0002
a
Vacuum packaging
Means within a row with no common letter di€er signi®cantly (p<0.05), n=4.
394
M. Du et al. / Meat Science 56 (2000) 387±395
Table 7
The o€-odora of raw chicken patties after 7 days of storageb
Nonirradiated
Irradiated
Diet
Aerobic packaginga
Vacuum packaginga
Aerobic packaging
Vacuum packaging
Control
1.25%
2.5%
5.0%
S.E.M.
5.7
5.2
6.2
4.3
0.76
3.6
3.8
4.1
5.6
0.76
6.0
6.7
6.1
4.5
0.70
7.5
7.8
6.5
8.3
0.80
Probability
Diet (D)
Irradiation (IR)
Packaging (P)
DIR
DP
IRP
DIRP
a
b
0.99
0.0001
0.4
0.5
0.007
0.0003
0.9
O€-odor: 0=no o€-odor, 15=strong o€-odor.
Means within a row with no common letter di€er signi®cantly (p<0.05), n=16.
signi®cant amounts of sulfur compounds were detected
in raw chicken meat under the conditions used in this
study.
4. Conclusion
Results showed that the TBARS values of meat patties decreased as the dietary CLA level increased. The
volatile composition of raw chicken meat was signi®cantly in¯uenced by dietary CLA levels and irradiation. Dietary CLA improved color stability, and sensory
panelists could not di€erentiate the odor of meat patties
from four di€erent CLA treatments. Vacuum packaging
virtually protected lipid oxidation and volatile production in both irradiated and nonirradiated raw chicken
meat during storage.
Acknowledgements
Paper No. J-18831 of the Iowa Agriculture and Home
Economics Experiment Station, Ames, IA 50011-3150.
Project No. 3322. This research has been supported by
the Hatch Act and CDFIN.
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