Structural and antioxidant properties of cowpea protein hydrolysates

Abstract

Cowpea protein isolates extracted at pH 8.0 (I8) and pH 10.0 (I10) were hydrolysed by alcalase to obtain limited (I8LH and I10LH) and extensive (I8HH and I10HH) hydrolysates. Hydrolysis degree was 2.3% for I8LH, 4.6% for I10LH, 25.8% for I8HH and 24.1% for I10HH. The effect of hydrolysis was assessed by using solubility-pH profile assay, exclusion chromatography, gel electrophoresis, infrared and fluorescence spectroscopy and surface hydrophobicity. Subsequently, ABTS.+, ORAC and HORAC methods were applied to measure antioxidant activity in all samples. Electrophoresis, chromatography and surface hydrophobicity showed different profiles for I8LH and I10LH, presumably, due to the initial extraction pH of protein isolates. Limited hydrolysis increased antioxidant activity in both I8LH and I10LH with values higher than 70% for ABTS.+, 60% for ORAC and 45% for HORAC when compared to their respective isolates. Concerning extensive hydrolysis, I8HH and I10HH yielded similar effects when considering physicochemical, functional and antioxidant properties. Both I8HH and I10HH showed increments above 80% for ABTS.+, 80% for ORAC and 70% for HORAC in comparison to their respective isolates. These results indicate that limited and extensive alcalase hydrolysis of both isolates increases antioxidant activity regardless of the pH for initial protein extraction. Finally, peptides with a molecular weight between 1.8 and 6.5 kDa (I8HH and I10HH from FPLC soluble fractions) exhibited the highest ORAC activity. Thus, cowpea alcalase hydrolysates emerge as viable ingredients to formulate foods with antioxidant properties.