Angiotensin I-converting-enzyme (ACE)-inhibitory activity of tryptic peptides of ovine beta-lactoglobulin and of milk yoghurts obtained by using different starters

The aim of this study was to investigate the angiotensin I-converting-enzyme ( ACE)inhibitory activity of tryptic hydrolysates of ovine beta-lactoglobulin, and of yoghurts made by using different starters. Ovine beta-lactoglobulin ( a mixture of variants A and B at a ratio of 50/50) was subjected to trypsin activity. The degree of hydrolysis of native whole beta-lactoglobulin reached 56, 72, 93 and 95\% after 1, 2, 8 and 24 h, respectively. ACE-inhibitory activity of tryptic hydrolysates increased with the time of hydrolysis, yielding 85, 88 and 92\% after 2, 12 and 24 h, respectively. The determination of ACE-inhibitory activity of some tryptic peptides separated by RP-HPLC and identified by mass spectroscopy showed that the more hydrophilic peptides showed the higher activity. Yoghurts obtained by fermentation of ovine milk with four different sets of starters, and their fractions soluble or not at pH 4.6 also showed an ACE-inhibitory activity. The maximum activity was obtained in the case of insoluble fractions at pH 4.6 of yoghurts made with the set of starters YC-183.