CHROMATOGRAPHIC QUANTITATION OF FREE AMINO-ACIDS - S-METHYLMETHIONINE, METHIONINE AND LYSINE IN CORN

The Pickering lithium gradient system was used with a modified Hewlett-Packard HPLC and post-column ninhydrin derivatization to separate and visualize the free amino acids and other ninhydrin-positive substances in corn (Zea mays). About 50 major and minor components were discernible, with generally very good separation. Analytical focus was on S-methylmethionine, principal precursor of the volatile flavor component dimethyl sulfide, in several sweet corn genotypes. The standard Pickering gradient program gave excellent separation of S-methylmethionine from the other basic amino acids, permitting detection of as little as 20 pmoles. Quantitation was highly reproducible when canavanine was used as internal standard. Free methionine and lysine were also measured.