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

Abstract

The breakdown of soy peptides by two strains of Prevotella ruminicola was studied. The percentage degradation by P ruminicola 23 was 30·8% (±0·6) and that by S17/3 was 14·3% (±4·0). Separation of the peptides by HPLC showed that the 2–3 kDa fraction decreased greatly during the course of fermentation 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 ruminicola is dependent on small peptides (<1 kDa). Among the peptidase activities that were studied, only the dipeptidyl amino peptidase type I (DAP-1) activity was expressed by both strains of P ruminicola. The hydrolysis of peptides by P ruminicola 23 is strongly dependent, therefore, on alanine aminopeptidase 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 reverse-phase HPLC and the analysis of the amino acid composition of the residual peptides were unable to show any enrichment of the culture medium in hydrophobic peptides during the growth phase of P ruminicola. The amino acid analysis corresponding to the hydrolysis of soy peptides by P ruminicola 23 showed a strong decrease in the proportion of Glu and an increase in the proportions 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. © 1998 Society of Chemical Industry.