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 angiotensi n I-converting enzyme (ACE) inhibitory activity. The bovine whey proteins a lpha-lactalbumin and beta-lactoglobulin were hydrolysed with pepsin, trypsi n, chymotrypsin, pancreatin, elastase or carboxypeptidase alone and in comb ination. The total hydrolysates were fractionated in a two step ultrafiltra tion process, first with a 30 kDa membrane and then with a 1 kDa membrane. Inhibition of ACE was analysed spectrophotometrically. The peptides were is olated by chromatography and identified by mass and sequencing analysis. Th e most potent inhibitory peptides were synthesized by the 9-fluorenylmethox ycarbonyl solid phase method. Inhibition of ACE was observed after hydrolys is with trypsin alone, and with an enzyme combination containing pepsin; tr ypsin and chymotrypsin. Whey protein digests gave a 50 % inhibition (IC50) of ACE activity at concentration ranges within 345-1733 mu g/ml. The IC50 v alues for the 1-30 kDa fractions ranged from 485 to 1134 mu g/ml and for th e < 1 kDa fraction from 109 to 837 mg/ml. Several ACE-inhibitory peptides w ere isolated from the hydrolysates by reversed-phase chromatography, and th e potencies of the purified peptide fractions had IC50 values of 77-1062 mu M. The ACE-inhibitory peptides identified were cr-lactalbumin fractions (5 0-52)1 (99-108) and (104-108) and beta-lactoglobulin fractions (22-25), (32 -40), (81-83). (94-100), (106-111) and (142-146).