Structural characterization of peroxyl radical oxidative products of antioxidant peptides from hydrolyzed proteins

This work aimed to characterize oxidative products of five unique antioxidant peptides (P1: YFDEQNEQFR, P2: GQLLIVPQ, P3: SPFWNINAH, P4: NINAHSVVY, P5: RALPIDVL) from hydrolyzed oat proteins. Peptides were reacted with 2,2'-Azobis(2-amidinopropane) dihydrochloride, a common peroxyl radical generator. Chromatographic data showed that peptide P3 was the most oxidized (67 ± 4 %) while also displaying the most ability to scavenge radicals in the oxygen absorbance capacity assay (ORAC) with an activity of 2.16 ± 0.09 μM Trolox equivalents/μM peptide. Structural characterization using mass spectrometry showed the presence of four oxidative products of P3, three of which were mono-oxygenated and the fourth di-oxygenated. The identification of these oxidative products is new and provides an opportunity to investigate their biological function. A good correlation (r = 0.889) between the degree of oxidation and the ORAC data, demonstrates the usefulness of using oxidative peptide data to predict their radical scavenging activities.