Study of enzyme activities and physicochemical parameters during hydrolysis of soy peptides by Prevotella ruminicola

The breakdown of soy peptides by two strains of Prevotella ruminicola was s tudied. The percentage degradation by P ruminicola 23 was 30.8% (+/-0.6) an d that by S17/3 was 14.3% (+/-4.0). Separation of the peptides by HPLC show ed that the 2-3 kDa fraction decreased greatly during the course of ferment ation when the 23 strain was present. Peptide analysis after 0 and 16 h of incubation by the S17/3 strain revealed an accumulation of peptides with a molecular weight of 1-2 kDa. This study shows that the growth of P ruminico la is dependent on small peptides (<1 kDa). Among the peptidase activities that were studied, only the dipeptidyl amino peptidase type I(DAP-1) activi ty was expressed by both strains of P ruminicola. The hydrolysis of peptide s by P ruminicola 23 is strongly dependent, therefore, on alanine aminopept idase and does not seem to be correlated with DAP-1 activity. In contrast, the hydrolysis of soy peptides by the S17/3 strain, which does not possess alanine aminopeptidase, is correlated with the activity of DAP-1. The rever se-phase HPLC and the analysis of the amino acid composition of the residua l peptides were unable to show any enrichment of the culture medium in hydr ophobic peptides during the growth phase of P ruminicola. The amino acid an alysis corresponding to the hydrolysis of soy peptides by P ruminicola 23 s howed a strong decrease in the proportion of Glu and an increase in the pro portions of Ala, Val and Thr (P < 0.05) during the course of fermentation. The amino-acid composition corresponding to the hydrolysis of soy peptides by P ruminicola S17/3 did not change significantly. (C) 1998 Society of Che mical Industry.