Proteolytic profiles of yogurt and probiotic bacteria

Abstract

Nine strains of Streptococcus thermophilus, 6 strains of Lactobacillus delbrueckii ssp. bulgaricus, 14 strains of Lactobacillus acidophilus and 13 strains of Bifidobacterium spp. were screened for proteolytic, amino-, di-, tri- and endopeptidase activity by using the o-pthaldialdehyde-based spectrophotometric assay. Strains showing the highest and lowest proteolytic activity were further studied for their peptidase activities at the extracellular and intracellular levels. The amounts of free amino groups released by S. thermophilus, L. delbrueckii ssp. bulgaricus and L. acidophilus strains were higher than by Bifidobacterium strains. Aminopeptidase activity was detected for all bacterial strains both at the extracellular and intracellular levels. The specific activity towards the six substrates studied was higher at the intracellular level for all strains. High dipeptidase activity was demonstrated by all bacterial strains for L. delbrueckii ssp. bulgaricus, L. acidophilus, and Bifidobacterium spp. whereas S. thermophilus had greater dipeptidase activity at the extracellular level. All bacterial cultures tested were able to hydrolyse large biologically active peptides, bradykinin, Ala-Ala-Ala-Ala-Ala and the tripeptide substrate Gly-Ala-Tyr at both the extracellular and intracellular levels. However, with the substrates ending with a C-terminal of phenylalanine, the hydrolysis only occurred at the intracellular level. (C) 2000 Elsevier Science Ltd.