Lipid Extraction and Distribution Studies of Egg Yolk Lipoproteins

The three lipoproteins of egg yolk, α- and β-lipovitellin and the low-density fraction (LDF), have been isolated and their lipid compositions determined. α- and β-lipovitellin comprise 22 to 26% lipid, of which 61% is phospholipid, 35% is triglyceride, and 4% is cholesterol and its esters. LDF contains about 89% lipid having 27% phospholipid, 69% triglyceride, and 4% cholesterol and cholesterol esters. The phospholipids of the three lipoproteins are similar, i.e., 74% lecithins, 18% cephalins, and 8% minor phospholipids. The fatty acid compositions of the neutral lipids, lecithins, and cephalins of the α- and β-lipovitellins were also similar, with only minor differences.Gentle extraction of the LDF solutions with ethyl ether readily removes about 85% of the total lipid and 55% of the phospholipid, while subsequent changes are slow. The lipoprotein residue contains 52% lipid which is mostly phospholipid; when the residual ether is removed, five sedimenting components are observed in the ultracentrifuge.