Effect of Protein Disruption by Denaturation and Hydrolysis on Egg Yolk Lipid Oxidation

Egg yolk (20%, w/w) was added to 1,3, and 6M guanidinium chloride (Gnd C1) solutions and agitated at 23°C. Thiobarbituric acid reactive substances (TBARS) were measured over a 2 week period. Increasing concentrations of Gnd C1 resulted in more rapid development of TBARS. Disodium ethylenediamine tetraacetate (EDTA; 2.0%) inhibited the formation of TBARS in 6M Gnd CI treated yolk, indicating a metal catalyzed reaction. Protein hydrolysis using 1% papain in the presence of added iron (FeC1 3 ) produced a significant increase (P<0.01) in conjugated dienes (233 nm) and trienes (270 nm). Increased lipid oxidation upon denaturation or hydrolysis of the protein moiety suggests that the ordered structure of lipid in the form of lipoprotein may partially account for the inherent oxidative stability of native yolk.