Isolation of peptides from a novel brewers spent grain protein isolate with potential to modulate glycaemic response

Summary The in vitro dipeptidyl peptidase‐ IV ( DPP ‐ IV ) inhibitory activity of a Brewers’ spent grain protein‐enriched isolate ( BSG ‐ PI ) Alcalase™ hydrolysate (AlcH), which had previously been identified as a relatively potent angiotensin‐converting enzyme ( ACE ) inhibitor, was determined. The half maximal DPP ‐ IV inhibitory concentration ( IC 50 ) value of AlcH following 240‐min digestion was 3.57 ± 0.19 mg mL −1 . Ultrafiltration fractionation did not significantly increase the DPP ‐ IV inhibitory activity of the AlcH fractions. Subjection of AlcH to simulated gastrointestinal digestion ( SGID ), which yielded SA lcH, resulted in a significant increase in DPP ‐ IV inhibitory activity ( P  <   0.05), particularly after the intestinal phase of digestion. Following semi‐preparative reverse phase high performance liquid chromatography ( RP ‐ HPLC ) fractionation of SA lcH, fraction 28 was identified as having highest mean DPP ‐ IV inhibitory activity. Two novel DPP ‐ IV inhibitory peptides, ILDL and ILLPGAQDGL , with IC 50 values of 1121.1 and 145.5 μ m , respectively, were identified within fraction 28 of SA lcH following ultra‐performance liquid chromatography ( UPLC )‐tandem mass spectrometry ( MS / MS ). BSG protein‐derived peptides were confirmed as having dual ACE and DPP ‐ IV inhibitory activities.