Seki_2020_J.Agric.Food.Chem__

Proteolytic products of bonito stock residue inhibit dipeptidyl peptidase-IV (DPP-IV). Here, we isolated, purified, and identified the components of its N5 fraction obtained after using neutral protease from Aspergillus oryzae. A 10%-ethanol eluent (N5-2 fraction) from column chromatography was sequenced, yielding 18 peptides. Of these, Glu-Val-Phe, Ala-Va-Phe, and Gly-Val-Phe were identified as novel (IC50 values for DPP-IV inhibition were 525.56, 5466.49, and 2870.87 microM , respectively), whereas Trp-Val is the primary peptide (IC50 value of 36.99 microM, 1359 unit (mL/100g-N5-2 fraction) = (yield (mg/)/100g-N5-2 fraction)/ IC50(microg/mL). Furthermore, the N5-2 fraction significantly decreased DPP-IV activity in Caco-2 intestinal epithelial cells (p<0.05). From the oral glucose tolerance test using ICR mice, the N5-2 fraction significantly attenuated the rise in serum glucose levels compared with the control (p<0.05) through cell-surface DPP-IV inhibition. We discuss the novelty, the significance and relevance of finding study as well as its broad applications of prevention with diabetes.