Antioxidant activity of peptide fractions from whey protein hydrolysates as measured by electron spin resonance

Whey protein isolate (WPI) was hydrolysed for 0.5–8 h using Alcalase, and the 5-h hydrolysate, identified to possess the strongest reducing ability, was subjected to column fractionation and antioxidant activity assays. Sephadex G-10 gel filtration chromatography of the 5-h hydrolysate yielded four fractions (I, II, III and IV) that were composed of peptides of >40k, 2.8–40k, 0.1–2.8k, and <0.1k, respectively. Fraction III exhibited the strongest free radical scavenging effects, which was evidenced by the electron spin resonance (ESR) of 1,1-diphenyl-2-picrylhydrazyl radicals (DPPH) and of trapped hydroxyl (OH) and superoxide (O2-) radicals. The results indicated that antioxidant activity of whey protein hydrolysates depended on peptide molecular weight, with peptides of 0.1–2.8k possessing the strongest radical scavenging activity.