The composition of avian egg yolk glycerides

A study was conducted to ascertain the influence of diet on the composition of chicken egg yolk glycerides. Triglycerides were isolated and characterized by successive chromatographic techniques. The fatty acid composition of vitelline phospholipids was determined by gas-liquid chromatography. Birds receiving a practical diet supplemented with 0 or 5% menhaden oil produced similar proportions of yolk triglyceride types with 0 to 3 or more double bonds per molecule. Hens fed a synthetic "fat-free" diet synthesized less triglycerides with 0 or 3+ ethylenic linkages per molecule but more mono- and di-unsaturated triglycerides than those on practical rations. These changes were related to the supply of exogenous linoleic acid and thus to the availability of this compound for triglyceride biosynthesis. Dietary polyunsaturated fatty acids present in menhaden oil were incorporated in yolk phospholipids to a greater extent than in vitelline triglycerides. The amount of linoleic acid found in yolk glycerides was commensurate to the content of this compound in the diet. Oleic effectively substituted linoleic acid in yolk glycerides when the latter was absent from the hen's diet. Preference for esterification at the 2- position of yolk triglycerides was linoleic > oleic > palmitic. The deposition of saturated acids in yolk glycerides was impervious to the type of diet fed to the laying hens.