Fatty Acid Distribution in Egg Yolk as Influenced by Type and Level of Dietary Fat

Abstract

Hens were fed diets containing 5, 10, 15, 22.2 or 30% of safflower oil; 22.2 or 30% of linseed oil; and 10% of cottonseed, corn, or soybean oil. The total fatty acids of the yolk fat were determined by alkaline isomerization and by gas-liquid chromatography and their distribution compared with that of eggs produced on a stock diet or on a low-fat diet. The linoleic acid content of eggs from hens fed safflower oil or cottonseed oil was approximately proportional to the level of linoleic acid in the diet. In eggs from hens fed diets containing linolenic acid (corn oil, soybean oil, linseed oil) linoleic acid was not deposited as efficiently as in those from hens fed safflower oil or cottonseed oil, suggesting an antagonistic or inhibitory effect of linolenic acid toward incorporation of linoleic acid into yolk fat. On all diets, except the linseed oil diets, the principal change accompanying an increase in linoleic acid was a corresponding decrease in oleic and palmitoleic acids. Only at about 40% of linoleic acid was there a slight decrease in palmitic acid level. No change occurred in the level of stearic acid. On the linseed oil diets the increases in yolk levels of polyunsaturated fatty acids were accompanied by decreases, not only in the monoenoic acids but also of palmitic acid, even though stearic acid remained unchanged. Levels of tetraenoic, pentaenoic and hexaenoic acids were low and variable on all diets. No changes that could be ascribed to the diet used were found in these acids.