Antioxidant and metal chelating activities of peptide fractions from phaseolin and bean protein hydrolysates

Bean protein isolate and phaseolin were hydrolysed using pepsin and pancreatin, and the resulting hydrolysates were filtered through a 1 kDa cut-off membrane and fractionated by size exclusion chromatography. Three fractions corresponding to MW 0.7–1.0 kDa, 0.43–0.7 kDa and <0.43 kDa (A1, A2, and A3 for protein isolate fractions, and B1, B2, and B3 for phaseolin fractions) were assayed for antioxidant and metal chelating activity and they were also subjected to amino acid and SDS–PAGE analysis. Fractions A1 and B1 had the highest copper chelating activity (78% and 82%, respectively), while iron chelating activity was the highest in fractions A1 and B3 (36% and 16%, respectively). Fractions A2 and B3 had the highest antioxidant activity as determined by inhibition of reducing power and β-carotene bleaching, while the highest ABTS radical scavenging activity was found in A3 and B3. Thus, fractions coming from the isolate and phaseolin had similar activities except for iron chelation, suggesting that phaseolin is the major contributor to the antioxidant and copper chelating activities of the hydrolysed protein isolate.