ACE-inhibition and imunomodulant activity of milk fermented with lactic acid bacteria isolated from traditional Italian dairy products

Milk proteins are precursors of different biologically active peptides. They are inactive within the sequence of the precursor proteins but can be released by enzymatic proteolysis, e.g. during the production of fermented milk by selected bacterial strains. Two of the most interesting biological activities recognised in milk peptides are angiotensin-I converting enzyme (ACE) inhibitory and immunomodulatory activity. The present work uses an enzymatic assay to identify ACE-inhibitory activity of standard milk fermented by two bacterial strains, Enterococcus faecalis TH563 and Lactobacillus delbrueckii subsp. bulgaricus LA2, isolated from local dairy products and selected for their different proteolytic activity. In addition, fermented milks were evaluated for immunomodulatory activity by studying the proliferation of bovine peripheral blood lymphocytes taken from nine nonpregnant, non-lactating, clinically healthy cows by the MTT test. Cells were incubated (3*106 cell mL-1) for 48h in a 96-well microplate with increasing concentrations of the two fermented milks, with or without concanavalin A (conA; 2μg mL-1). E. faecalis TH563 produced a fermented milk with a greater ACE-inhibitory activity (69.43%±3.12) than L. delbrueckii subsp. bulgaricus LA2 (60.86%±1.01) (P<0.05). These data may be due to the potential capacity of TH563 strain to produce peptides from proteins, suggested also by its highest proteolytic activity. The evaluation of immunomodulatory activity showed a great inter-animal variability. The administration of different concentrations of both fermented milks in absence of conA did not significantly affect BPBL proliferation, while milk fermented by L. delbrueckii subsp. bulgaricus LA2 significantly inhibited BPBL proliferation at concentration of 5-25-50 μg mL-1 in presence of conA (P<0.05; 83% in comparison with the control). E. faecalis TH563 did not significantly modify cell proliferation at any concentration used. In conclusion, L. delbrueckii subsp. bulgaricus LA2 could be a suitable strain for the production of fermented milk with biofunctional activity. Further studies should be carried out to evaluate its application for the production of milk derived foods.