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 pept ide residue produced by hydrolysis of protein by two strains of Prevotella ruminicola (23 and S17/3) were determined. These last two characteristics c ould play a role in the control of proteolysis. Both strains produced dipep tidyl peptidases (DAP-1) but only P. ruminicola 23 synthesised alanine amin opeptidase. The area of 3-5 kDa peptides decreased, while the peptides dire ctly assimilable by bacteria (0.5-1 kDa and < 0.5 kDa) increased with strai n S17/3, but decreased with P. ruminicola 23. The amino acid compositions s howed that the proportions of these compounds changed little with time and there was no proline enrichment. Similarly, reverse phase HPLC showed no ev idence of enrichment of the culture medium by hydrophobic peptides during t he growth phase of P. ruminicola. These experiments show that the changes i n the various peptide classes resulting from the hydrolysis and uptake of p eptides 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 m ay explain the difference between the two strains. (C) Inra/Elsevier, Paris .