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

The in vitro dipeptidyl peptidase-IV (DPP-IV) inhibitory activity of a Brewers' spent grain proteinen-iched isolate (BSG-PI) AlcalaseTM 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 (IC50) 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 SAlcH, 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 SAlcH, fraction 28 was identified as having highest mean DPP-IV inhibitory activity. Two novel DPP-IV inhibitory peptides, ILDL and ILLPGAQDGL, with IC50 values of 1121.1 and 145.5 mu M, respectively, were identified within fraction 28 of SAlcH 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.