Proteolytic activity of dairy lactic acid bacteria and probiotics as determinant of growth and in vitro angiotensin-converting enzyme inhibitory activity in fermented milk

Two strains each of Lactobacillus acidophilus (L10 and La 4962), Bifidobacterium spp. ( B. lactis B94 and B. longum B1536), and Lactobacillus casei (L26 and Lc 279), and one strain each of Streptococcus thermophilus (St 1342) and Lactobacillus delbrueckii ssp. bulgaricus (Lb 1466) were assessed for growth characteristics, proteolytic activity and release of in vitro angiotensin-converting enzyme inhibitory peptides in reconstituted skim milk. Single cultures grew well with exception of Lactobacillus delbrueckii ssp. bulgaricus. Despite slow growth, this culture produced substantial amount of lactic acid, second to S. thermophilus. All strains exhibited proteolytic activities with intra- and extracellular specific peptidases including X-prolyl-dipeptidyl aminopeptidase. The latter cleaved proline-containing sequences, which possibly enhanced liberation of various peptides and likely resulted in improved cell growth. The extent of proteolysis varied among strains and appeared to be time dependant. All the cultures released peptides with in vitro ACE-inhibitory activity during growth with B. longum Bl 536 and L. acidophilus L10 having IC50 values of 0.196 and 0.151 mg . mL(-1), respectively.