EFFECT OF PROTEOLYTIC MODIFICATION AND METHIONINE ENRICHMENT ON THE NUTRITIONAL-VALUE OF SOYA ALBUMINS FOR RATS

Proteolytic modification, particularly when combined with methionine e nrichment, significantly reduced the lectin content and modified the t rypsin inhibitor activity of a soya albumin preparation. During both p eptic hydrolysis and enzymatic peptide modification, the amount of soy a bean agglutinin was reduced. This reduction was verified by the decr ease in the intensity of protein staining and immunoblots of the pepti c hydrolysate and of the product produced by enzymatic peptide modific ation, and confirmed by haemagglutination activity measurements and EL ISA technique. The functional activity of Kunitz trypsin inhibitor was also partially abolished whereas that of the Bowman-Birk inhibitor wa s not significantly altered by the enzymatic modifications. In line wi th the reduction in some of the antinutrients, the nutritional perform ance of rats fed a diet containing this enzymatically modified product was significantly improved in comparison with that of the control ani mals fed the original soya albumin but was poorer than the lactalbumin -fed controls. Enzymatic peptide modification of soya albumin fraction s by transpeptidation and covalent methionine enrichment is suitable t o improve their nutritional value partly by compensating for their met hionine deficiency and partly by modifying the structure of the soya a ntinutrients. Changes in the structure by proteolytic hydrolysis and s ynthesis of peptide chains can lead to alteration in protein conformat ion resulting in modified biological activity and increased nutritiona l value.