Antidiabetic Potential of Protein Hydrolysates and Peptide Fractions from Lima Bean (Phaseolus lunatus L): An In Vitro Study

Characterized by uncontrolled, long-term high blood sugar levels, diabetes mellitus affects ever increasing numbers of people worldwide. Type 2 diabetes is the most common, accounting for 95% of reported cases. The main objective of this article was to evaluate the in vitro antidiabetic effects of hydrolysates from Lima bean (Phaseolus lunatus L.) proteins. The hydrolysates were produced with either the Alcalase (R)-Flavourzyme (R) (AF) or pepsin-pancreatin (PP) sequential systems and peptide fractions (F > 10, F5-10, F3-5, 1-3 and < 1 kDa) isolated from them. Assays of in vitro inhibitory activity against the enzymes alpha-amylase, alpha-glucosidase, and dipeptidyl peptidase IV (DPP-IV) were done for all the hydrolysates and peptide fractions. Degree of hydrolysis (DH) was highest in the AF hydrolysates. Protein hydrolysates (PH) or ultrafiltered peptide fractions (UFPF) test concentrations (mg protein mL(-1)) were in alpha-amylase, PP (100 mg mL(-1)) and AF (50 mg mL(-1)); alpha-glycosidase, PP (200 mg mL(-1)) and AF (10 mg mL(-1)); and DPP-IV, PP and AF (10 mg mL(-1)). Among the AF products, inhibitory activities were highest in the F > 10 kDa fraction against alpha-amylase (IC50 = 54.61 +/- 1.76 mg protein mL(-1)), the F5-10 kDa (IC50 = 124.14 +/- 3.05) against alpha-glucosidase and the F5-10 kDa (IC50 = 1.93 +/- 0.20) against DPP-IV. For the PP products, inhibitory activities were highest in the F < 1 kDa (IC50 = 55.79 +/- 1.06). None of the highly inhibitory hydrolysates or peptide fractions exhibited cytotoxicity in vitro versus Vero cells. These fractions are potential ingredients for inclusion in functional foods aimed at controlling type 2 diabetes.