Angiotensin i‐converting enzyme inhibitory and antioxidant peptide fractions from hard‐to‐cook bean enzymatic hydrolysates

The acceptability and marketability of hard‐to‐cook (HTC) bean has reduced. Protein isolates from HTC bean were hydrolyzed with one of two sequential enzymatic systems: Alcalase‐Flavourzyme or pepsin‐pancreatin. These hydrolysates were fractionated into five peptide fractions (>10, 5–10, 3–5, 1–3; and <1 kDa) using an ultrafiltration membrane system. Fraction angiotensin I‐converting enzyme (ACE) inhibitory (IC₅₀) and antioxidant activities (trolox equivalent antioxidant capacity [TEAC]) were measured: the <1 kDa fractions exhibited the highest values for both activities. These fractions were further purified by gel chromatography in a Sephadex C‐50 column (Pharmacia, Uppsala, Sweden), producing 11 peptide fractions (F0‐F10) from each <1 kDa fraction. The highest IC₅₀ value (2.7 µg protein/mL) was observed in F6 from the Alcalase‐Flavourzyme hydrolysate, and the highest TEAC value (6,922.0 mM/mg sample) was observed in F10 from the pepsin‐pancreatin hydrolysate. HTC bean protein hydrolysates and their fractions are promising natural ACE inhibitors and antioxidants, and potential ingredients in functional food systems. PRACTICAL APLICATIONS: Biofunctional peptides have the potential to be applied in the formulation of health‐enhancing nutraceuticals with well‐defined pharmaceutical effects. Peptide products that have angiotensin I‐converting enzyme (ACE) inhibitory effect are currently on the market and some of them are at the stage of being tested because of the strict requirements in order to demonstrate the efficacy of these bioactive peptides prior to their widespread utilization as physiologically beneficial functional foods/food ingredients. Many peptides and protein hydrolysates can lower the pace of lipid autoxidation process. They also play a role of the heavy metal acceptors and scavenge‐free radicals. Protein hydrolysates can potentially be applied as additives to many of food products although their darkening and low fat solubility make it impossible to apply them as the antioxidative additives to fats and oils. Hard‐to‐cook bean protein hydrolysates and their peptide fractions are promising natural ACE inhibitors and antioxidants, and potential ingredients in functional food systems.