Analysis for and Generation of Cholesterol Oxidation Products in Egg Yolk by Heat Treatment

Certain oxidation products of cholesterol exhibit a much greater biopotency for inducing atherogenesis, cell cytotoxicity, and inhibiting cholesterol biosynthesis than cholesterol. Early studies involving the feeding of cholesterol may have been complicated by the presence of unsuspected contamination by these oxidation products. As a result, investigations were undertaken to develop methods of analysis for cholesterol oxides and to determine if these substances are present in fresh egg yolk and in egg yolk heated in air. Both reversed phase high pressure liquid chromatography and direct adsorption high pressure liquid chromatography were applied to show that fresh egg yolk contains small amounts of polar cholesterol derivatives. Those given tentative identification by cochromatography with known standards are: 25-hydroxycholesterol, 7-hydroxycholesterol, and 7-ketocholesterol. Heating egg yolk for 100 hr at 100 C in air increased the amounts of these compounds fourfold and changed the amount of other unidentified polar substances. The metabolic and biological significance of these findings remain to be determined.