Dietary Conjugated Linoleic Acid with Fish Oil Alters Yolk n-3
and Trans Fatty Acid Content and Volatile Compounds
in Raw, Cooked, and Irradiated Eggs1
G. Cherian,*,2 M. P. Goeger,* and D. U. Ahn†
*Department of Animal Sciences, Oregon State University, Corvallis, Oregon 97331-6702; and
†Department of Animal Sciences, Iowa State University, Ames, Iowa 50011-3150
ABSTRACT We investigated the effect of dietary conjugated linoleic acid (CLA) along with n-3 polyunsaturated
fatty acid (n-3 PUFA) on yolk fatty acid composition and
volatile compounds in eggs that were raw (RA), hardboiled (HB), or hard-boiled, irradiated (HBI, 2.5 kGy).
Single Comb White Leghorn laying hens (n = 40) were
randomly assigned to one of the four experimental diets
containing 0, 0.5, 1.0, or 2.0% CLA. Menhaden oil was
used as the source of n-3 PUFA. Eggs collected after 6
wk of feeding were analyzed for fatty acids and volatile
compounds. The content of docosahexaenoic acid (C22:6
n-3) was reduced (P < 0.05) in eggs from hens fed the 2.0%
CLA diet. Eggs from hens fed 0.5% CLA incorporated the
highest concentration of docosahexaenoic acid (P < 0.05)
with a concomitant reduction in arachidonic acid (P <
0.05). The yolk contents of cis-9 trans-11 CLA and trans10 cis-12 CLA increased linearly (P < 0.05) as the dietary
CLA supply increased. Total monounsaturates were reduced (P < 0.05) with an increase in saturates in yolk. No
difference was observed in the total PUFA content of
eggs. Total volatiles were reduced in RA eggs from 1.0
and 2.0% CLA diets. 2-Propanone, hexane, and methyl
cyclopentane were the major volatiles in RA eggs and
were reduced by dietary CLA at 1.0 and 2.0%. Acetaldehyde, pentane, propanol, acetic acid methyl ester, acetic
acid ethyl ester, propionic acid methyl ester, 2-methylmethyl propionic acid, 2-propanone, and octane were the
major volatiles in HB eggs and were reduced by 2.0%
CLA (P < 0.05). No difference was observed in the acetaldehyde, pentane, propanol, acetic acid ethyl ester, octane,
or total volatile content of HBI eggs.
(Key words: conjugated linoleic acid, egg, n-3 polyunsaturated fatty acid, irradiation, volatiles)
2002 Poultry Science 81:1571–1577
INTRODUCTION
Conjugated linoleic acid (CLA) is the generic name for
a group of positional and geometric conjugated dienomic
isomers of linoleic acid and has received considerable
attention for its anticarcinogenic, antiatherogenic, and hypocholestrolemic properties (Pariza et al., 2001). Other
beneficial effects of CLA include body fat reduction, immuno-modulation, and antioxidant properties (Cook et
al., 1993; Cantwell et al., 1999; DeLany et al., 1999). Humans cannot synthesize CLA; it is contributed to the human diet by food lipids of ruminant origin such as milk
and beef. Current intake of CLA is estimated to be several
hundred milligrams per day (Fritsche et al., 1999). However, considering the variation in CLA content of food
products, these estimates are questionable. Based on ani-
2002 Poultry Science Association, Inc.
Received for publication December 4, 2001.
Accepted for publication May 9, 2002.
1
Journal paper number 11851 of the Oregon Agriculture Experiment
Station, Corvallis, OR 97331-6702; Project No 00501.
2
To whom correspondence should be addressed: gita.cherian
@orst.edu.
mal data, it is estimated that approximately 3 g/d of CLA
would be required to produce beneficial effects in humans
(Ha et al., 1989). However, as Americans are opting for
low-fat dairy products and choosing more poultry foods
than beef, it is likely that dietary contribution of CLA will
further be reduced in a typical US diet.
CLA, when associated with food, has been reported to
have higher tissue retention and better anticancer effects
than commercially available supplements (Ip et al., 1999).
In this respect, CLA-enriched chicken poultry foods may
be an alternative vehicle for delivering health-promoting
fatty acids to consumers.
Feeding CLA to hens can contribute substantially to
the energy content (Sell et al., 2001) and also increase the
CLA content of tissues and yolk (Ahn and Sell, 1999;
Chamruspollert and Sell, 1999; Jones et al., 2000). These
researchers used soy oil or canola oil along with CLA to
feed laying hens. Recently, Cherian et al. (2001) used
Abbreviation Key: CLA = conjugated linoleic acid; HB = hard-boiled;
HBI = hard-boiled, irradiated; MUFA = monounsaturated fatty acids;
PUFA = polyunsaturated fatty acids; SFA = saturated fatty acids; RA
= Raw.
1571
1572
CHERIAN ET AL.
fish oil [as source of n-3 polyunsaturated fatty acid (n-3
PUFA)] along with CLA in the diet of laying hens to
produce n-3 PUFA-CLA-rich eggs. Incorporating PUFA
and CLA into eggs may influence the stability of lipids
and fatty acids and may change the volatiles of eggs.
However, no information is available on the influence
of PUFA and CLA on the volatile profiles of raw and
cooked eggs.
Irradiation of foods including eggs has gained as an
effective tool for assuring food safety and controlling bacteria such as salmonella (Rajkowski and Thayer, 2000).
However, one concern with irradiation is increased lipid
peroxidation due to production of free radicals. Eggs high
in PUFA may be more susceptible to lipid oxidation.
Therefore, irradiation can lead to increased production
of lipid peroxidation products and lower consumer acceptability. Feeding CLA has been reported to reduce
PUFA in eggs (Du et al., 1999). Therefore, PUFA-CLArich eggs may be less susceptible to irradiation-induced
lipid peroxidation. The hypothesis for the present study
is that CLA may reduce the PUFA content of eggs, resulting in the formation of less lipid oxidation products.
The consumer acceptability of PUFA-CLA-modified eggs
also depends on odor and sensory quality characteristics.
The objectives of the present study were to determine the
influence of dietary PUFA and CLA on yolk fatty acids
and CLA incorporation and to determine the volatile profiles of raw (RA), hard-boiled (HB), hard-boiled and irradiated (HBI) eggs.
MATERIALS AND METHODS
These experiments were reviewed by the Oregon State
University Animal Care Committee to ensure adherence
to Animal Care Guidelines.
TABLE 1. Composition and calculated analysis
of the laying hen diets1
Dietary CLA level (%)1
Ingredients
0
0.5
Corn
Soybean meal
Limestone
Calcium phosphate
Layer premix2
Fish oil
CLA
Salt
DL-Methionine
Calculated analyses
Crude protein
ME, kcal/kg
Calcium
Available phosphorus
60.6
24.6
6.0
1.5
0.3
3.0
0.0
0.35
0.1
60.6
24.6
6.0
1.5
0.3
2.5
0.50
0.35
0.1
1.0
2.0
(% of diet)
16.5
2,938.5
3.7
0.8
16.5
2,938.5
3.7
0.8
60.6
24.6
6.0
1.5
0.3
2.0
1.0
0.35
0.1
16.5
2,938.5
3.7
0.8
60.6
24.6
6.0
1.5
0.3
1.0
2.0
0.35
0.1
16.5
2,938.5
3.7
0.8
1
All diets contained corn and soybean meal, with added CLA at 0,
0.5, 1.0, or 2.0%.
2
Supplied per kilogram of the diet the following: vitamin A, 8.25
KIU/kg; vitamin D, 2.64 KIU/kg; vitamin E, 16.5 KIU/kg; riboflavin,
5.28 mg/kg; niacin, 26.4 mg/kg; vitamin B12, 8.91 MCG/kg; biotin, 0.099
mg/kg; pyridoxine, 1.32 mg/kg; thiamine, 1.155 mg/kg; selenium, 0.264
mg/kg; manganese, 90.4 mg/kg; zinc, 92.4 mg/kg.
cooking, and volatile compounds assay (six eggs per treatment per assay).
Egg Cooking
Prior to hard boiling eggs were maintained at room
temperature for 24 h. Eggs (n = 6 per treatment) were
cooked at 98 C for 30 min, cooled in ice water for 20 min,
and equilibrated at room temperature for 15 min (Cherian
et al., 1990). HB and RA eggs were shipped by overnight
express to Iowa State University for volatile analysis.
Birds and Diets
A total of 40 Single Comb White Leghorn laying hens
were kept in individual cages and were fed corn-soybean
meal-based diets with added CLA at 0, 0.5, 1.0, and 2.0%.
The control diet (0% CLA) contained 3% menhaden oil,
and the CLA source was substituted for menhaden oil
on a weight:weight basis. The composition of the diet is
shown in Table 1. The CLA source, which contained 75%
free fatty acid, was obtained from a commercial source
and contained 34.9% cis-9 trans-11, and 35.9% trans-10
cis-12 CLA isomers.3 The diets were prepared biweekly
and kept at 4 C in airtight containers. Hens were fed the
experimental diets for 42 d.
Sample Collection
Eighteen eggs per treatment, collected from Days 40
through 42 of feeding, were taken for fatty acid analysis,
3
Pharmanutrients, Lake Bluff, IL.
Lipid and Fatty Acid Analyses
Total lipids were extracted from egg yolks by the
method of Folch et al. (1957). One gram of yolk was
weighed into a screw-capped test tube with 20 mL of
chloroform:methanol (2:1, vol/vol) and was homogenized with a Polytron for 5 to 10 s at high speed. The
homogenate was filtered through Whatman no. 1 filter
paper into a 100-mL graduated cylinder, and 5 mL of
0.88% sodium chloride solution was added and mixed.
After phase separation, the volume of the lipid layer was
recorded, and the top layer was removed by siphon. Three
milliliters of the lipid extracts was dried in a block heater
under nitrogen atmosphere and used for fatty acid analyses. The dried lipids were redissolved in 2 mL borontrifluoride-methanol methylation solution (Cherian et al.
1996) and were incubated in a boiling water bath for 1 h
at 90 to 100 C (Wang et al., 2000). After cooling to room
temperature, the fatty acid methyl esters were separated
by hexane and distilled water. Analysis of fatty acid composition was performed with a HP 6890 gas chromato-
1573
CONJUGATED LINOLEIC ACID AND EGG VOLATILES
graph4 equipped with an autosampler, flame ionization
detector, and SP-2560 fused silica capillary column (100
m × 0.25 mm × 0.2-µm film thickness).5 Two microliters
of sample was injected with helium as carrier gas (1.0
mL/min) onto the column. The initial column temperature was set at 110 C, held for 0.5 min, increased by 20.0
C/min to 200 C, and held for 50 min. The temperature
was then increased by 10.0 C/min to 230 C and held for
5.0 min. Inlet and detector temperatures were 250 C. Peak
areas and percentages were calculated using HP ChemStation software.4 Fatty acid methyl esters were identified
by comparison with retention times of authentic standards.6 Fatty acid values and total lipids were expressed
as weight percentages.
Irradiation
HB eggs were packaged in oxygen-permeable plastic
bags and irradiated at 0 or 2.5 kGy using a Linear Accelerator.7 The energy and power level used were 10 MeV and
10 kW, respectively, and the average dose rate was 89.0
kGy/min. To confirm the target dose, two alanine dosimeters per cart were attached to the top and bottom surfaces
of the sample. The alanine dosimeter was read using a
104 Electron Paramagnetic Resonance instrument.8
Volatile Compound Analysis
A purge-and-trap apparatus9 connected to gas chromatograph-mass spectrometer4 was used to analyze the volatiles responsible for the off-odor in samples. A 2-g sample
was placed in a 40-mL sample vial that had been flushed
with helium gas (99.99%) for 5 s. The egg sample was
then purged with helium gas (40 mL/min) for 15 min.
Volatiles were trapped at 20 C using a Tenax column,9
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 HP-624 column,
250-µm i.d. with 1.4 µm nominal; a 52-m HP-1 column,
250-µm i.d. with 0.25 µm nominal; and an 8-m HP-wax
column 250-µm i.d. with 0.25 µm nominal combined using zero dead-volume column connectors were used for
volatile analysis. Ramped oven temperature was used (0
C for 2.5 min, increased to 10 C at 2.5 C/min, to 45 C at
10 C/min, to 110 C at 20 C/min, to 180 C at 10 C/min,
and held for 2.5 min). Inlet temperature was 180 C. Liquid
nitrogen was used to cool the oven below ambient temperature. Helium was the carrier gas at constant pressure
of 20.5 psi.
The ionization potential of mass spectrometry was 70
eV and the scan range was 18.1 to 300 m/z. Identification
of volatiles was achieved by comparing mass spectral
4
Hewlett Packard Co., Wilmington, DE.
SP-2560, Supelco, Bellefonte, PA.
6
Matreya Inc, Pleasant Gap, PA.
7
Circe IIIR, Thomson CSF Linac, Saint-Aubin, France.
8
Bruker Instruments Inc., Billerica, MA
9
Tekmar-Dohrmann, Cincinnati, OH.
5
TABLE 2. Major fatty acid composition of egg yolk as influenced
by hen diets containing different levels of conjugated linoleic acid1
Dietary CLA level (%)1
Fatty acids (%)
16:0
18:0
18:1 n-9
18:2 n-6
20:4 n-6
22:6 n-3
Cis-9 trans-11 CLA2
Trans-10 cis-12 CLA
Total CLA
Total SFA
Total MUFA
Total PUFA
0
28.5b
8.7c
38.2a
11.6
0.7ab
3.0c
0.0d
0.0c
0.0d
38.3c
41.4a
16.0
0.5
(% of total
33.8a
16.2b
24.7b
12.2
0.5b
4.2a
0.8c
0.16c
0.97c
51.3b
26.8b
18.1
1.0
2.0
SEM
lipids)
34.7a
19.7a
20.9c
12.0
0.7ab
3.8b
1.6b
0.8b
2.4b
55.5a
22.4c
17.7
35.3a
20.7a
17.4d
12.9
0.8a
2.5d
3.6a
1.6a
5.3a
56.8a
18.7d
17.6
0.46
0.52
0.58
0.52
0.06
0.10
0.06
0.08
0.13
0.67
0.40
0.57
a-d
Means within a row with no common superscript differ (P < 0.05);
n = 6.
1
All diets contained corn and soybean meal, with added CLA at 0,
0.5, 1.0, or 2.0%. CLA was substituted for menhaden oil on a
weight:weight basis.
2
CLA = conjugated linoleic acid; SFA = saturated fatty acids, MUFA
= monounsaturated fatty acids; PUFA = polyunsaturated fatty acids.
data of samples with those of the Wiley Library and standards when available. The area of each peak was integrated using the ChemStation software,4 and the total ion
counts (peak area × s) × 104 were reported as an indicator
of volatiles generated from the egg samples.
Statistical Analyses
The effects of dietary CLA on yolk fatty acids and
volatile compounds were analyzed by ANOVA using
SAS software (SAS Institute, 1985). Student-NewmannKeul’s multiple-range test (Steel and Torrie, 1980) was
used to compare differences among treatment means (P
< 0.05). Means and SEM are reported.
RESULTS AND DISCUSSION
The CLA content of the egg yolk increased significantly
in a dose-dependent manner with the dietary CLA content. At 2.0% CLA, yolks showed the highest incorporation of CLA. The total yolk CLA was 5.3% with the 2.0%
CLA diet but was 0% with the control diet (P < 0.05)
(Table 2). The major CLA isomer in the yolk lipids was
cis-9 trans-11 isomer, which was 0, 0.8, 1.6, and 3.6% in
the yolk lipids of hens fed 0, 0.5, 1.0, or 2.0% CLA diets,
respectively. The content of trans-10 cis-12 CLA isomer
constituted 0, 0.16, 0.8, and 1.6% of yolk lipids from hens
fed diets containing 0, 0.5, 1.0, or 2.0% CLA, respectively.
Addition of 2% CLA to diets resulted in greater than
50% reduction of monounsaturated fatty acids (MUFA)
and was replaced by saturated fatty acids (SFA). These
results also corroborate with those reported by Chamruspollert and Sell (1999) and Du et al. (1999). ∆9-Desaturase
is responsible for the conversion of stearic acid (18:0) to
oleic acid (18:1). Dietary CLA may have inhibitory effect
on desaturases, which may lead to reduction of MUFA.
1574
CHERIAN ET AL.
TABLE 3. Volatile profiles of raw egg yolk as influenced by hen
diets containing different levels of conjugated linoleic acid (CLA)1
Dietary CLA level (%)1
Volatiles
0
Oxybis methane
1,1-Oxybis ethane
2-Propanone
Hexane
Methyl cyclopentane
Total
120d
144ab
1,368a
1,470a
865a
3,966a
0.5
1.0
2.0
SEM
(total ion counts × 104)
338c
534b
770a
113b
147ab
200a
1,071ab
454b
476b
1,159a
623b
329b
1,013a
422b
236b
3,694a
2,180b
2,011b
40
20
206
162
170
314
a,b
Means within a row with no common superscript differ (P < 0.05);
n = 6.
1
All diets contained corn, soybean meal, and fish oil with added CLA
at 0, 0.5, 1.0, or 2.0%. SEM = standard error of the mean.
Choi et al. (2000) also reported that a decrease in mRNA
expression of steroyl coenzyme A in CLA-fed rats affected
the synthesis of MUFA and accumulation of SFA. The
SFA contents of eggs from hens fed 1.0 and 2.0% CLA
were higher (P < 0.05) than hens fed 0 and 0.5% CLA
diets. These results suggest an inhibitory effect of CLA
on enzymes responsible for MUFA synthesis, resulting
in accumulation of SFA. Dietary CLA did not alter the
total n-6 and n-3 PUFA contents of yolk.
The volatile profiles of raw eggs are shown in Table 3.
No volatile unique to eggs from hens fed CLA diets were
identified, indicating that the changes were quantitative.
The total amount of volatiles was reduced (P < 0.05) in
eggs from hens fed diets containing 1.0 and 2.0% CLA.
Alkanes and ketones were the major volatiles in raw eggs
and were reduced in eggs from 1.0 and 2.0% CLA eggs.
The contents of 2-propanone, hexane, and cyclopentane
were reduced (P < 0.05) as the diet concentration of CLA
increased. Production of volatiles is closely related to
oxidative changes in eggs. Irrespective of the higher total
PUFA (n-6 + n-3) content of eggs from the 2.0% CLA diet,
the reduction in volatile components may suggest that
dietary CLA has a protective effect on lipid oxidation,
thereby increasing the oxidative stability.
Cooking resulted in a significant increase in volatile
compounds in HB eggs. Formation of flavor compounds
may be initiated in the lipid portion of food during heating, resulting in an increase in volatiles of HB eggs. A
total of 25 volatiles were identified and quantitated in
the HB eggs (Table 4). Those volatiles in the greatest
concentrations in CLA-rich eggs (1.0 and 2.0% CLA diets)
were pentane and hexane and were reduced (P < 0.05)
by dietary CLA. Volatile classes such as sulfides, furans,
esters and ketones, and total volatiles were reduced in
eggs from hens fed 1.0 and 2.0% CLA diets. Dimethyl
sulfide and other sulfur compounds are derived from
degradation of amino acids and are associated with irradiated odor formation (Ahn et al., 2000). Brown et al. (1986)
reported the odor of dimethyl sulfide as sulfurous, or
“bad eggs,” and was associated with spoilage of egg com-
TABLE 4. Volatile profiles of cooked egg yolk as influenced by hen diets
containing different levels of conjugated linoleic acid (CLA)1
Dietary CLA level (%)1
Volatiles
/
2-Methyl-1-propene
Butane
Acetaldehyde
2-Butene
Pentane
2-Pentene
Propanol
2-Propanone
Thiobismethane
Acetic acid methyl ester
2-Methylpropanal
Hexane
Butanal
2-Butanone
Acetic acid ethyl ester
Propionic acid methyl ester
Benzene
3-Methylbutane
Heptane
2-Methylmethyl propionic acid
2-Ethylfuran
Pentanal
Dimethyl disulfide
Toulene
Octane
Total
0
21b
113c
1,362a
0b
3,545b
0b
718b
713a
671
5,535a
0b
708c
0b
463
3,712
842ab
147a
244a
238
1,237ab
729a
181a
645a
250
82ab
22,153b
0.5
1.0
(total ion counts × 104)
175a
109a
374b
667a
0c
760b
2,644a
0b
5,229b
10,329a
462a
452a
3,729a
1,388b
0b
0b
1,232
319
9,099a
0b
282a
289a
1,417c
5,322a
192a
0b
305
317
17,220
154
1,434a
0b
0b
0b
187b
0c
438
420
1,758a
0b
447b
229c
142a
0b
185b
0b
170
198
185a
158a
a
47,305
21,109b
2.0
SEM
142a
406b
801b
0b
6,659b
569a
1,362b
0b
459
0b
236a
3,304b
0b
803
0
0b
0b
0c
295
0b
302c
0b
0b
209
0b
15,545b
25
66
158
208
936
68
585
0
304
1,175
24
510
34
153
4,437
233
3
18
68
389
25
22
54
23
38
5,926
Means within a row with no common superscript differ (P < 0.05); n = 6.
All diets contained corn, soybean meal, and fish oil with added CLA at 0, 0.5, 1.0, or 2.0%. CLA was substituted
for menhaden oil on a weight:weight basis.
a-c
1
1575
CONJUGATED LINOLEIC ACID AND EGG VOLATILES
TABLE 5. Volatile profiles of cooked egg yolk from hen diets containing
different levels of conjugated linoleic acid (CLA) after irradiation1
Dietary CLA level (%)1
Volatiles
Cyclopropane
2-Methyl propane
2-Methyl-1-propene
Butane
Acetaldehyde
2-Butene
1,4 Pentadienone
1-Pentene
Pentane
2-Pentene
Propanol
2-Propanone
Thiobismethane
Acetic acid methyl ester
2-Methyl propanal
1-Hexene
Hexane
2-Hexene
Butanal
2-Butanone
Acetic acid ethyl ester
Propionic acid methyl ester
Benzene
3-Methylbutane
1-Heptene
Heptane
2-Methyl-methyl propionic acid
2-Ethylfuran
Pentanal
1-Heptyne
1-Methyl-1-4-cyclopentane
Dimethyl disulfide
Toulene
1-Octene
Octane
2-Octene
3-Methyl-2-heptene
Octyne
Total
0
141
193
9,670
9,921
16,023
1,153
0b
4,625
31,993a
1,232b
9,000a
6,161
3,729
442c
2,150
2,953
18,901a
0b
2,122a
2,294b
609
0c
756
1,157
4,358
5,691
156b
243c
425b
552
0b
240b
503
858
1,718ab
0b
0b
0b
139,967
0.5
1.0
(total ion counts × 104)
154
121
197
187
8,972
8,243
6,771
8,087
13,887
23,228
1,310
1,226
78a
0b
3,739
3,939
13,563b
21,171ab
898b
249b
5,428b
13,039a
11,649
12,513
2,231
1,191
12,590a
7,002b
2,089
1,781
2,342
2,236
4,299c
7,683bc
0b
195a
577b
2,030a
1,477b
2,373b
6,521
2,937
1,331a
509b
769
842
1,389
1,709
4,036
3,927
2,911
5,048
823a
604ab
a
1,098
901b
487b
485b
577
597
0b
213a
a
571
307b
518
490
430
929
605b
1,791ab
b
0
505b
0b
501a
0b
374a
114,311
141,410
2.0
SEM
126
218
10,065
9,721
16,143
1,164
0b
4,854
27,675a
20,567a
11,148a
8,810
1,156
562c
2,060
2,835
13,026b
200a
2,241a
4,280a
10,246
0c
940
2,209
4,709
5,946
233b
543c
5,149a
588
223a
292b
576
1,163
2,206a
1,062a
501a
360a
173,797
14
47
678
914
2,696
91
3
389
3,332
4,157
1,144
1,530
807
1,570
273
286
1,864
21
180
459
4,424
127
105
319
581
886
130
60
766
71
29
71
68
209
371
161
71
34
14,530
Means within a row with no common superscript differ (P < 0.05); n = 6.
All diets contained corn, soybean meal, and fish oil with added CLA at 0, 0.5, 1.0, or 2.0%. CLA was substituted
for menhaden oil on a weight:weight basis.
a-c
1
ponents. Dimethyl sulfide is formed by degradation of
sulfur-containing amino acids. The content of methionine
or other sulfur containing amino acids in the CLA eggs
is not known in the present study.
The absence of dimethyl sulfide in eggs from 1.0 and
2.0% CLA eggs may suggest a protective effect of dietary
CLA on the degradation of sulfur containing amino acids.
The two ketones identified in cooked eggs were 2-propanone and 2-butanone and were reduced (P < 0.05) in 1.0
and 2.0% CLA-eggs. Ketones in foods have been implicated with off-flavors referred to as “perfume” rancidity
(Stokoe, 1928). Propanol was the only alcohol detected in
eggs and was higher in eggs from the 0.5% CLA diet
when compared to other treatments. The reason is not
known for low content of propanol in HB eggs from hens
on 1.0 or 2.0% CLA in diet.
The contribution of alcohols to flavors of foods has
been reported to be minor (Heath and Reineccius, 1986).
Aromatic compounds such as benzene were not detected
in eggs from CLA-fed hens. The occurrence of lipid and
fatty acid oxidation is often associated with deleterious
changes in food flavors (Frankel, 1984). PUFA are more
susceptible to lipid oxidation. Fatty acids of the n-6 family
(linoleic and arachidonic acid) are suggested to be the
precursors of hexanal (Meynier et al., 1999). Hexanal and
pentanal contents in volatiles are suggested to be good
indicators of oxidation (Ahn et al., 1998). Pentanal was
not detected in HB eggs from 1.0 and 2.0% CLA diets
when compared to eggs from 0 and 0.5% CLA diets.
Irradiation is one of the most efficient methods available for ensuring microbiological food safety (Rajkowski
and Thayer, 2000). However, irradiation has been reported to increase lipid oxidation and off-odor (Ahn et
al., 1998, 1999). The effects of irradiation on PUFA-CLArich eggs are not known. In the present study, a total of
38 different volatiles were identified and quantitated in
HBI eggs. Irradiation resulted in an increase (P < 0.05) in
the ion counts of total volatiles in all eggs. No difference
1576
CHERIAN ET AL.
was noted in the total volatiles of control or CLA-rich
eggs.
Alkanes, alkenes, and aldehydes were the major volatiles in HBI eggs (Table 5). As the content of CLA in the
eggs increased, irradiation resulted in an increase in the
ion counts of volatiles such as pentanal, pentane, 2-hexene, 2-butanone, 1-methyl-1,4-cyclopentane, octane, 2-octene, 3 methyl-2-heptene, and octyne (P < 0.05). When
molecules absorb ionizing energy, they become reactive
and form ions or free radicals, which further leads to
an increase in oxidation products. Lipid oxidation byproducts are considered important volatiles related to
the off-odor in irradiated meat (Jo and Ahn, 2000). The
presence of dimethyl sulfide in HBI eggs from hens fed
a diet containing 0.5% CLA was higher (P < 0.05) than
all other treatments. The reason for this difference is not
known. No significant changes in the amount of irradiation-sensitive compounds, such as 1-heptene and 1-heptyne, were observed in eggs. The absence of irradiationsensitive compounds in eggs with high PUFA and CLA
may suggest lipid stability and increased sensory quality
of n-3 PUFA-modified eggs. The ion counts of other volatiles related to irradiation, such as 2-methyl butanal was
not different among treatments (P > 0.05).
In conclusion, these studies support the theory that
irradiation leads to high ion counts volatiles in cooked
eggs. However, no specific volatile compounds unique
to irradiation were observed in HBI eggs with high CLA
content. Further elucidation of changes in volatile compounds associated with CLA and n-3 PUFA enrichment
of eggs and their effects on product quality after cooking
and or irradiation may be critical for maintaining overall
flavor quality of eggs and egg products and consumer
acceptability of such egg-based foods.
ACKNOWLEDGMENTS
The Ott Professorship awarded to G. Cherian is acknowledged. The CLA used in this study was kindly
supplied by Pharmanutrients, Lake Bluff, IL. The assistance of the Oregon State University Poultry Farm staff
is acknowledged. The generous donation of menhaden
oil from Omega Protein Inc, Reedville, VA, is appreciated.
Our sincere thanks are also extended to D. Holtan of the
Department of Animal Sciences, Oregon State University,
for gas chromatography help.
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