Characterization and analysis of antioxidant activity of walnut-derived pentapeptide PW5 via nuclear magnetic resonance spectroscopy

•Nuclear Magnetic Resonance (NMR) characterization of walnut-derived peptide PW5.•PW5 exhibited significant antioxidant activity using ABTS assay in vitro.•The oxidized products after PW5 reacted with ABTS were explored by NMR.•Trp residue was the most critical determining factor for PW5 antioxidant activity.•NMR method may be a useful way to explore antioxidant mechanisms of peptides. The antioxidative activity of natural products has commonly been studied by free radical scavenging methods. However, the mechanisms by which antioxidation is explored by free radical scavenging methods remain largely unknown. This study analyzed the composition of walnut-derived pentapeptides PW5 with potential biological activity and its oxidation reaction products in 2,2′-Azinobis-(3-ethylbenzthiazoline-6-sulphonate) (ABTS) test by nuclear magnetic resonance (NMR) spectroscopy. The amino acid sequence of PW5 peptide successfully characterized as Proline-Proline-Lysine-Asparagine-Tryptophan exhibited significant antioxidant activity with lower IC50 value (0.2210 ± 0.0032 mM) compared to glutathione (GSH, 0.2567 ± 0.0023 mM, p