Sequential alcalase and flavourzyme treatment for preparation of α-amylase, α-glucosidase, and dipeptidyl peptidase (DPP)-IV inhibitory peptides from oat protein

The current study reported oat protein as a precursor for alpha-amylase, alpha-glucosidase, and dipeptidyl peptidase (DPP)-IV inhibitory peptides and studied the antidiabetic activities related to their structures. Enzyme inhibition assays in vitro, using oat protein treated by alcalase and flavourzyme fractionated into different molecular weights and hydrophobicity, indicated that the relatively hydrophobic fraction of 1-5 kDa inhibited enzymes related to glucose digestion, absorption, and metabolism activities. The alpha-amylase and DPP-IV were inhibited 57 and 78%, respectively, even at low peptide concentrations. LC-MS/MS analysis of the most effective fractions disclosed two eight amino acid sequences, identified from 12S oat globulin (GDVVALPA and DVVALPAG), and other sequences rich in amino acids like proline, leucine, valine, phenylalanine, and glutamine. The results suggest that proline and hydrophobic amino acids may favor hydrophobic interactions and hydrogen bonding with the target enzymes, especially the Leu-Pro sequence found in potent DPP-IV inhibitors.