Angiotensin I-converting enzyme inhibitory properties of whey protein digests:: concentration and characterization of active peptides

The aim of this study was to identify whey-derived peptides with angiotensin I-converting enzyme (ACE) inhibitory activity. The bovine whey proteins alpha-lactalbumin and beta-lactoglobulin were hydrolysed with pepsin, trypsin, chymotrypsin, pancreatin, elastase or carboxypeptidase alone and in combination. The total hydrolysates were fractionated in a two step ultrafiltration process, first with a 30 kDa membrane and then with a 1 kDa membrane. Inhibition of ACE was analysed spectrophotometrically. The peptides were isolated by chromatography and identified by mass and sequencing analysis. The most potent inhibitory peptides were synthesized by the 9-fluorenylmethoxycarbonyl solid phase method. Inhibition of ACE was observed after hydrolysis with trypsin alone, and with an enzyme combination containing pepsin; trypsin and chymotrypsin. Whey protein digests gave a 50 % inhibition (IC50) of ACE activity at concentration ranges within 345-1733 mu g/ml. The IC50 values for the 1-30 kDa fractions ranged from 485 to 1134 mu g/ml and for the < 1 kDa fraction from 109 to 837 mg/ml. Several ACE-inhibitory peptides were isolated from the hydrolysates by reversed-phase chromatography, and the potencies of the purified peptide fractions had IC50 values of 77-1062 mu M. The ACE-inhibitory peptides identified were cr-lactalbumin fractions (50-52)1 (99-108) and (104-108) and beta-lactoglobulin fractions (22-25), (32-40), (81-83). (94-100), (106-111) and (142-146).