Factors Governing Lysinoalanine Formation in Soy Proteins

Exposing soy protein to alkaline conditions (pH 8‐14) for various time periods (10‐480 min), and temperatures (25‐95°C at 10°C intervals) destroyed all of the cystine and part of arginine, lysine, serine, and threonine residues. These losses were accompanied by the appearance of lysinoalanine (LAL) and unidentified ninhydrin‐positive compounds. Acylation of the proteins minimized LAL formation. Addition of cysteine, copper salts, dimethyl sulfoxide and glucose also suppressed LAL production. Oxygen, with one possible exception, did not affect LAL formation. Free and protein‐bound lysinoalanine is stable to acid but not basic conditions used for protein hydrolysis. Mechanisms are described to explain the observed influence of these variables on LAL generation.