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 conju- 0.05). The yolk contents of cis-9 trans-11 CLA and trans- gated linoleic acid (CLA) along with n-3 polyunsaturated 10 cis-12 CLA increased linearly (P < 0.05) as the dietary fatty acid (n-3 PUFA) on yolk fatty acid composition and CLA supply increased. Total monounsaturates were re- < volatile compounds in eggs that were raw (RA), hard- duced (P 0.05) with an increase in saturates in yolk. No boiled (HB), or hard-boiled, irradiated (HBI, 2.5 kGy). difference was observed in the total PUFA content of Single Comb White Leghorn laying hens (n = 40) were eggs. Total volatiles were reduced in RA eggs from 1.0 and 2.0% CLA diets. 2-Propanone, hexane, and methyl randomly assigned to one of the four experimental diets cyclopentane were the major volatiles in RA eggs and containing 0, 0.5, 1.0, or 2.0% CLA. Menhaden oil was were reduced by dietary CLA at 1.0 and 2.0%. Acetalde- used as the source of n-3 PUFA. Eggs collected after 6 hyde, pentane, propanol, acetic acid methyl ester, acetic wk of feeding were analyzed for fatty acids and volatile acid ethyl ester, propionic acid methyl ester, 2-methyl- compounds. The content of docosahexaenoic acid (C22:6 methyl propionic acid, 2-propanone, and octane were the < n-3) was reduced (P 0.05) in eggs from hens fed the 2.0% major volatiles in HB eggs and were reduced by 2.0% CLA diet. Eggs from hens fed 0.5% CLA incorporated the CLA (P < 0.05). No difference was observed in the acetal- highest concentration of docosahexaenoic acid (P < 0.05) dehyde, pentane, propanol, acetic acid ethyl ester, octane, with a concomitant reduction in arachidonic acid (P < 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 mal data, it is estimated that approximately 3 g/d of CLA would be required to produce beneficial effects in humans Conjugated linoleic acid (CLA) is the generic name for (Ha et al., 1989). However, as Americans are opting for a group of positional and geometric conjugated dienomic low-fat dairy products and choosing more poultry foods isomers of linoleic acid and has received considerable than beef, it is likely that dietary contribution of CLA will attention for its anticarcinogenic, antiatherogenic, and hy- further be reduced in a typical US diet. pocholestrolemic properties (Pariza et al., 2001). Other CLA, when associated with food, has been reported to beneficial effects of CLA include body fat reduction, im- have higher tissue retention and better anticancer effects muno-modulation, and antioxidant properties (Cook et than commercially available supplements (Ip et al., 1999). al., 1993; Cantwell et al., 1999; DeLany et al., 1999). Hu- In this respect, CLA-enriched chicken poultry foods may mans cannot synthesize CLA; it is contributed to the hu- be an alternative vehicle for delivering health-promoting man diet by food lipids of ruminant origin such as milk fatty acids to consumers. and beef. Current intake of CLA is estimated to be several Feeding CLA to hens can contribute substantially to hundred milligrams per day (Fritsche et al., 1999). How- the energy content (Sell et al., 2001) and also increase the ever, considering the variation in CLA content of food CLA content of tissues and yolk (Ahn and Sell, 1999; products, these estimates are questionable. Based on ani- 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 2002 Poultry Science Association, Inc. Received for publication December 4, 2001. Accepted for publication May 9, 2002. 1Journal paper number 11851 of the Oregon Agriculture Experiment Abbreviation Key: CLA = conjugated linoleic acid; HB = hard-boiled; Station, Corvallis, OR 97331-6702; Project No 00501. HBI = hard-boiled, irradiated; MUFA = monounsaturated fatty acids; 2To whom correspondence should be addressed: gita.cherian PUFA = polyunsaturated fatty acids; SFA = saturated fatty acids; RA @orst.edu. = Raw. 1571 1572 CHERIAN ET AL. fish oil [as source of n-3 polyunsaturated fatty acid (n-3 TABLE 1. Composition and calculated analysis of the laying hen diets1 PUFA)] along with CLA in the diet of laying hens to produce n-3 PUFA-CLA-rich eggs. Incorporating PUFA Dietary CLA level (%)1 and CLA into eggs may influence the stability of lipids Ingredients 0 0.5 1.0 2.0 and fatty acids and may change the volatiles of eggs. However, no information is available on the influence (% of diet) of PUFA and CLA on the volatile profiles of raw and Corn 60.6 60.6 60.6 60.6 Soybean meal 24.6 24.6 24.6 24.6 cooked eggs. Limestone 6.0 6.0 6.0 6.0 Irradiation of foods including eggs has gained as an Calcium phosphate 1.5 1.5 1.5 1.5 Layer premix2 0.3 0.3 0.3 0.3 effective tool for assuring food safety and controlling bac- Fish oil 3.0 2.5 2.0 1.0 teria such as salmonella (Rajkowski and Thayer, 2000). CLA 0.0 0.50 1.0 2.0 However, one concern with irradiation is increased lipid Salt 0.35 0.35 0.35 0.35 DL-Methionine 0.1 0.1 0.1 0.1 peroxidation due to production of free radicals. Eggs high Calculated analyses in PUFA may be more susceptible to lipid oxidation. Crude protein 16.5 16.5 16.5 16.5 Therefore, irradiation can lead to increased production ME, kcal/kg 2,938.5 2,938.5 2,938.5 2,938.5 Calcium 3.7 3.7 3.7 3.7 of lipid peroxidation products and lower consumer ac- Available phosphorus 0.8 0.8 0.8 0.8 ceptability. Feeding CLA has been reported to reduce 1All diets contained corn and soybean meal, with added CLA at 0, PUFA in eggs (Du et al., 1999). Therefore, PUFA-CLA- 0.5, 1.0, or 2.0%. rich eggs may be less susceptible to irradiation-induced 2Supplied per kilogram of the diet the following: vitamin A, 8.25 lipid peroxidation. The hypothesis for the present study KIU/kg; vitamin D, 2.64 KIU/kg; vitamin E, 16.5 KIU/kg; riboflavin, is that CLA may reduce the PUFA content of eggs, re- 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 sulting in the formation of less lipid oxidation products. mg/kg; manganese, 90.4 mg/kg; zinc, 92.4 mg/kg. 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 cooking, and volatile compounds assay (six eggs per treat- and CLA incorporation and to determine the volatile pro- ment per assay). files of raw (RA), hard-boiled (HB), hard-boiled and irra- diated (HBI) eggs. Egg Cooking MATERIALS AND METHODS Prior to hard boiling eggs were maintained at room temperature for 24 h. Eggs (n = 6 per treatment) were These experiments were reviewed by the Oregon State cooked at 98 C for 30 min, cooled in ice water for 20 min, University Animal Care Committee to ensure adherence and equilibrated at room temperature for 15 min (Cherian to Animal Care Guidelines. et al., 1990). HB and RA eggs were shipped by overnight express to Iowa State University for volatile analysis. Birds and Diets Lipid and Fatty Acid Analyses A total of 40 Single Comb White Leghorn laying hens were kept in individual cages and were fed corn-soybean Total lipids were extracted from egg yolks by the meal-based diets with added CLA at 0, 0.5, 1.0, and 2.0%. method of Folch et al. (1957). One gram of yolk was The control diet (0% CLA) contained 3% menhaden oil, weighed into a screw-capped test tube with 20 mL of and the CLA source was substituted for menhaden oil chloroform:methanol (2:1, vol/vol) and was homoge- on a weight:weight basis. The composition of the diet is nized with a Polytron for 5 to 10 s at high speed. The shown in Table 1. The CLA source, which contained 75% homogenate was filtered through Whatman no. 1 filter free fatty acid, was obtained from a commercial source paper into a 100-mL graduated cylinder, and 5 mL of and contained 34.9% cis-9 trans-11, and 35.9% trans-10 0.88% sodium chloride solution was added and mixed. cis-12 CLA isomers.3 The diets were prepared biweekly After phase separation, the volume of the lipid layer was and kept at 4 C in airtight containers. Hens were fed the recorded, and the top layer was removed by siphon. Three experimental diets for 42 d. milliliters of the lipid extracts was dried in a block heater under nitrogen atmosphere and used for fatty acid analy- Sample Collection ses.