Formation of Ne-carboxymethyllysine in raw and heat-treated hen eggs: Effects of egg freshness

This study aimed to evaluate the effects of storage duration (0, 8, 16, 24, 32 d; 22 C, 75% relative humidity) or freshness of hen eggs on the levels of protein-bound Ne-carboxymethyllysine (CML) in the albumen and yolk of raw eggs and their heat-treated (80 C, 6 min; 100 C, 30 min) counterparts. The mean CML level of raw albumen was significantly affected (p = 0.001) by the storage time of eggs, which was increased by 127% during the 32 d of storage. In addition, after 8, 16, 24 and 32 d storage of raw eggs, the average CML levels in their heat-treated albumen increased by 17%, 23%, 113%, and 157%, respectively, compared to that without storage (3.56 +/- 2.32 mg/kg). This promoting effect of increased storage duration of raw eggs on the CML formation in albumen was somewhat tied to the continuous increase of pH and decrease of Haugh units. However, the storage time of eggs had no noticeable effect on the CML levels of either raw or heat-treated yolk, implying the great disparity in the major compounds and/or chemical reactions contributing to CML formation between the yolk and albumen of hen eggs.