Quantification of racemization of amino acids in alkaline-treated duck eggs by micellar capillary electrophoresis

Duck eggs were pickled in 4.2% NaOH/5% NaCl solution for 20 days to prepare the traditional Chinese Pidan. The extent of racemization of compositional amino acid in egg albumen and yolk over the alkaline pickling period was investigated with micellar capillary electrophoresis (MCE) using beta-cyclodextrin as chiral selector. The racemization value of amino acids in egg albumen was in the order serine > aspartic acid > glutamic acid > phenylalanine > leucine > valine > threonine = isoleucine, whereas the order in egg yolk was aspartic acid > glutamic acid > phenylalanine > leucine > valine. Therefore, the tendency of amino acid racemization appeared to be closely related to the properties of its residual side chain, as well as the pH and alkaline treating period. Moreover, racemization of most of the amino acids was remarkably induced by the alkaline treatment during the initial pickling period.