Determination of bioactive peptide production capacities of some Enterococcus species in milk

Milk proteins are recognized as rich sources of bioactive peptides. It has however been demonstrated that the effect of bioactive peptides on angiotensin converting enzyme (ACE) inhibition is dependent upon bacterial strains/species and time. In the present work, 21 wild strains of two different Enterococcus species (Ent. faecium and Ent. faecalis) isolated from traditional fermented dairy products were tested regarding their ACE-I inhibition activities. In this regard, UHT milks were inoculated with Enterococcus strains separately and the fermented milks were stored 30 days at 4 ? C. Results obtained indicated that no clear correlation was evident between the counts of Ent. faecium and Ent. faecalis colonies and their ACE inhibition capacities. In all samples, the ACE inhibition ratios were between 46.13% and 89.61% at the beginning of storage period. The variation in the ACE inhibition capacities of the strains tested over the time course showed a strain-dependent characteristics. The ACE inhibiton capacities of six strains of Ent. faecium decreased by 2.95%-19.16% during cold storage, the ACE inhibition capacities of nine strains incraesed by 7.15%-32.43 in the same period. These figures were recorded as 1.0%-28.73% (four strains) and 1.80%-36.92% (two strains) for Ent. faecalis. No direct relationship was also recorded between OPA proteolysis, electrophoresis and %ACE inhibition ratios of the strains. Regarding IC50 values, the ACE inhibition capacities of the strains were well below the medicines used in treatment of hypertension.