Lysinoalanine: Production, significance and control in preparation and use of soya and other food proteins

Abstract

Formation of lysinoalanine (LAL) in proteins in response to alkali treatment is a well-known phenomenon. The quantity of LAL formed depends on temperature, the time of exposure to alkali, the type of protein, the concentration of protein and alkali in some instances, and probably the type of cation in the alkaline solution. Higher temperatures, longer exposure times, and higher pH’s generally result in more LAL formation. The addition of mercaptoethanol or cysteine to an alkaline protein solution decreases LAL formation markedly; lanthionine is apparently a major product formed when cysteine is added to an alkaline protein solution. Some LAL is likely to be formed in any protein-containing product that is subjected to alkaline treatment, and has been shown to be formed in some protein products under extreme heat conditions. Proper control of temperature and pH in processing can reduce or eliminate LAL formation. LAL has not been shown to present a toxicological hazard to any species other than the rat. Its presence in large quantities in any protein indicates destruction of cysteine and lysine; the nutritional inferiority of severely alkali- or heat-treated proteins due to LAL formation, amino acid degradation and isomerization, Maillard product formation, and so on is well documented. The small quantities of dietary LAL in food products currently on the market seem to represent no health hazard; the reduced nutritional quality of protein products that contain relatively high levels of LAL should be considered when these products are major sources of dietary protein.