Stability of Shell Egg and Liquid Yolk to Lipid Oxidation

Abstract Oxidative stability of the lipids, including cholesterol, of shell egg and broken-out liquid yolk was investigated. The oxidation of total yolk lipids was determined by peroxide value and measurement of thiobarbituric acid reactive substances (TBRS), and the presence of oxidized cholesterol derivatives was monitored by gas chromotography. After 18 months of refrigerated storage (4 C), shell egg yolk lipids had undergone very little oxidative deterioration. No measurable peroxides were present in the yolk of fresh, 12-, or 18-month eggs. Measurements of TBRS gave relatively low values that did not increase during storage. Chromatograms of yolk sterols indicated very little difference between fresh and 18-month eggs. None of the typical cholesterol oxides were detected based on relative retention time. During 3 weeks of storage, liquid yolk held at 45 and 55 C underwent partial gelation prior to increases in TBRS while yolk stored at lower temperatures (23 and 35 C) did not show measurable oxidative deterioration. In view of its high content of susceptible lipid constituents, egg yolk manifests an unusual stability toward lipid oxidation.