The proteolytic activity of various strains of yoghurt and probiotic bacteria, particularly their amino-, di-, tri- and endo-peptidase activities was studied. Nine strains of
Streptococcus thermophilus, 6 strains of Lactobacillus delbrueckii ssp. bulgaricus, 14 strains of Lactobacillus acidophilus and 13 strains of Bifidobacterium ssp. were screened for proteolytic activity by using the o-phthaldialdehyde based spectrophotometric assay. Those strains showing the highest and lowest proteolytic activity were further studied for their peptidase activities at the extracellular and intracellular levels. Aminopeptidase
activities were measured using chromogenic substrates (p-nitroanilide derivatives of Lanomers of leucine, lysine, alanine, proline, arginine, and methionine). Dipeptidase
activities were measured using dipeptides including Ala-Met, Leu-Tyr, Leu-Gly, Ala-His, and Pro-lLe as substrates. Endopeptidase and tripeptidase activities were detected using thin-layer chromatography.