Systemic screening of milk protein-derived ACE inhibitors through a chemically synthesised tripeptide library

A tripeptide library consisting of 373 tripeptides (nine repeats) based on bovine α-S1 casein and β-lactoglobulin was synthesised chemically, purified by HPLC and the angiotensin-converting enzyme (ACE) inhibitory activities were assayed. Of the 364 tripeptides assayed, 144 showed a relative ACE inhibitory activity higher than 50% and 43 higher than 60%, at a set concentration of 2.5 mM. More potent tripeptides were found from α-S1 casein than from β-lactoglobulin. The high percentage of Pro/Tyr in caseins could be the reason for this. Fifteen tripeptides with relative activities higher than 50% were selected and assayed for their IC50, using hippuryl-l-histidyl-l-leucine as the substrate. The most potent peptide showed an IC50 of 0.85 μM.