Angiotensin I-converting enzyme inhibitory activity of enzymatic hydrolysates of goat milk protein fractions

Casein and whey protein fractions from goat milk were hydrolysed by subtilisin and trypsin, individually and in combination, to release angiotensin converting enzyme (ACE)-inhibitory peptides. Selected hydrolysates were fractionated by size exclusion chromatography (SEC) and further characterised. The highest ACE-inhibitory activity was obtained from the casein fraction hydrolysed by the combination of enzymes. SEC presented 4 fractions with fraction F2 (<2.3 kDa) containing the highest concentration of peptides and the highest activity. F2 contained a number of peptides not previously identified from caprine caseins but with structural similarity to other ACE-inhibitory peptides. The most active fraction in relation to protein content was F4 with IC50 between 9.3 and 5.1 μg mL−1. This fraction contained a compound tentatively identified as WY, an active dipeptide not previously reported from caseins. The high inhibitory capacity of these fractions points towards the advantage of implementing a membrane process to concentrate the most active peptides.