Hard-to-cook bean (Phaseolus vulgaris L.) proteins hydrolyzed by alcalase and bromelain produced bioactive peptide fractions that inhibit targets of type-2 diabetes and oxidative stress

The objective was to evaluate the effect of bioactive peptide fractions from de-hulled hard-to-cook (HTC) bean on enzyme targets of type-2 diabetes and oxidative stress. Protein isolates from Pinto Durango and Negro 8025 beans were hydrolyzed (120 min) with either alcalase® or bromelain and separated into five peptide fractions (< 1, 1-3.5, 3.5-5, 5-10, and > 10 kDa) using an ultrafiltration membrane system. The < 1 kDa pinto Durango-bromelain fraction showed the best inhibition of α-amylase (49.9 ± 1.4%), and the < 1 kDa pinto Durango-alcalase fraction inhibited both, α-glucosidase (76.4 ± 0.5%), and dipeptidyl peptidase-IV (DPP-IV, 55.3 ± 1.6%). Peptides LLSL, QQEG and NEGEAH were present in the most potent fractions. Hydrolysates and peptide fractions showed antioxidant capacity (ORAC: 159.6 ± 2.9 to 932.6 ± 1.1 mmol TE/g) and nitric oxide inhibition (57.5 ± 0.9 to 68.3 ± 4.2%). Hydrolysates and fractions < 1 and 1-3 kDa were able to increase glucose-stimulated insulin secretion from iNS-1E cells up to 57% compared to glucose control. Hydrolysates from HTC beans inhibited enzymes related to diabetes management, being the smallest peptides (< 1 kDa) the most potent. HTC bean could be a source of protein to produce bioactive peptides with potential antidiabetic properties.