Selective release of ACE-inhibiting tryptophan-containing dipeptides from food proteins by enzymatic hydrolysis

Enzymatic hydrolysis of hen egg white lysozyme led to hydrolysates with pronounced inhibition of angiotensin I-converting enzyme (ACE). Two dipeptides, alanyl-tryptophan (AW) and tryptophanyl-tryptophan (WW), were identified for the first time in lysozyme hydrolysates by LC–ESI-TOF-MS and quantified by RP-HPLC-UV/fluorescence. Hydrolysis conditions were established for enhanced release of ACE-inhibiting tryptophan-containing dipeptides from alpha-lactalbumin and hen egg white lysozyme. The highest ACE inhibition potency and release of tryptophan-containing dipeptides were observed for the hydrolysates prepared by chymotrypsin followed by thermolysin. All identified dipeptides showed a significant and competitive inhibitory effect on ACE activity (AW: IC50 = 20 μmol/L; WW: IC50 = 68 μmol/L, IW: IC50 = 0.7 μmol/L, WL: IC50 = 10 μmol/L) in vitro and proved to be moderate resistant towards simulated gastrointestinal digestion. Protein hydrolysates containing tryptophan-containing dipeptides are interesting candidates as ingredients for functional foods with possible blood pressure-lowering effect, but also as a good source for the amino acid tryptophan.