Fractionation and identification of ACE-inhibitory peptides from α-lactalbumin and β-casein produced by thermolysin-catalysed hydrolysis

The thermolysin catalysed hydrolysates of alpha-lactalbumin and beta-casein were fractionated by size-exclusion chromatography (SEC) and reversed-phase high performance liquid chromatography (RP-HPLC) in order to identify the peptides responsible for the high ACE-inhibitory activity of these hydrolysates. The SEC fractionation separated many co-eluting peptides into different fractions allowing individual peptides to be isolated in one or two subsequent semi-preparative RP-HPLC fractionation steps. Five potent ACE-inhibitory peptides from alpha-lactalbumin were isolated. They all contained the C-terminal sequence -PEW, corresponding to amino acid residues 24-26 in alpha-lactalbumin, and had IC50 values of 1-5 mu m. From one SEC fraction of the beta-casein hydrolysate two potent ACE-inhibitory peptides were isolated and identified as f58-76 and f59-76 of beta-casein A2. They both contained IPP as the C-terminal sequence and had IC50 values of 4 and 5 mu m. From another SEC fraction a new but less ACE-inhibitory peptide from beta-casein was identified (f192-196; LYQQP). (C) 2007 Elsevier Ltd. All rights reserved.