In vitro study of molecular weight, hydrophobicity and amino acid composition of peptides during breakdown of a casein hydrolysate by two strains of Prevotella ruminicola.

The molecular weight, amino acid composition and hydrophobicity of the peptide residue produced by hydrolysis of protein by two strains of Prevotella ruminicola (23 and S17/3) were determined. These last two characteristics could play a role in the control of proteolysis. Both strains produced dipeptidyl peptidases (DAP-1) but only P. ruminicola 23 synthesised alanine aminopeptidase. The area of 3-5 kDa peptides decreased, while the peptides directly assimilable by bacteria (0.5-1 kDa and < 0.5 kDa) increased with strain S17/3, but decreased with P. ruminicola 23. The amino acid compositions showed that the proportions of these compounds changed little with time and there was proline enrichment. Similarly, reverse phase HPLC showed no evidence of enrichment of the culture medium by hydrophobic peptides during the growth phase of P. ruminicola. These experiments show that the changes in the various peptide classes resulting from the hydrolysis and uptake of peptides by P. ruminicola differed with time and depended on the strain used. The nature of the enzyme activity and the use of other nitrogen sources may explain the difference between the two strains.