STUDIES ON THE FORMATION OF LYSINOMETHYLALANINE AND HISTIDINOMETHYLALANINE IN MILK-PRODUCTS

From reaction mixtures consisting of N-acetyldehydroaminobutyric acid methyl ester and N(alpha)-acetyl-L-lysine or N(alpha)-acetyl-L-histidi ne, respectively, distinct amounts of the cross-link amino acids silon )-(2-amino-2-carboxy-l-methyl-ethyl)-L-lysine (lysinomethylalanin, LMe AL) and -(2'-amino-2'-carboxy-1'-methyl-ethyl)-L-histidine (histidinom ethylalanine, HMeAL) were isolated via praparative ion-exchange chroma tography and identified by H-1- and C-13-nuclear magnetic resonance. I n the amino acid chromatogram, both compounds eluted clearly separated from other basic amino acids. However, neither LMeAL nor HMeAL could be detected in numerous acid hydrolysates of a range of milk products. In model studies, threonine showed a significantly lower tendency for an alkali-induced beta-elimination reaction compared to serine. The r eactivity of the resulting dehydroaminobutyric acid towards nucleophil es was more than tenfold lower as compared to dehydroalanine. Thus, th e formation of LMeAL as well as of HMeAL during food processing is neg ligible.