Effect of diet on triglyceride structure and composition of egg yolk lipids

Abstract

Hens were fed a practical diet supplemented and unsupplemented with 5% menhaden oil and a synthetic fat-free diet for a period of 90 days. Egg yolks from hens fed each of the three diets were analyzed for fatty acid composition and positional distribution of the fatty acids by successive chromatographic techniques. The triglycerides were resolved into fractions containing, 0, 1, 2 and 3+ double bonds per molecule. Each of these types was quantitated and analyzed for fatty acid distribution. The positional distribution was determined with the aid of pancreatic lipase hydrolysis. The feeding of the practical diet supplemented with 5% menhaden oil produced an increase in the 14∶0 acid in the intact triglycerides, 2-monoglycerides and 1,3-diglycerides with the majority of this acid being bound in the 1,3 positions. In the monounsaturated triglycerides the 16∶0 acid was linked predominantly at the 1,3 positions. The feeding of the fat-free diet produced a decrease in the 16∶1 acid content of the egg yolk lipids in the monounsaturated series, in the intact triglycerides, the 2-monoglycerides and the 1,3-diglycerides. The 18∶0 acid was linked more often at the 1,3 positions than at the 2 position, and was not affected by the diet consumed by the hens. Hens fed the fat-free diet produced more monounsaturated and diunsaturated triglycerides than those fed the other diets. Linoleic acid exhibited the greatest degree of preference for the 2 position, which was followed in turn by oleic acid. All other major acyl components were found to be preferentially esterified at the 1,3 positions. The difference observed in the fatty acid composition of egg yolk neutral and polar lipids was attributable to the fatty acid content of the diet. In the case of the oleic and linoleic acids, there was less variation in the saturated fatty acid content, which could be traced to the type of diet fed.