| Summary: | Antioxidant activities of amino acids and synthetic dipeptides were studied to elucidate the structure–activity relationship of antioxidant dipeptides. Results showed that Tyr- and Trp-containing dipeptides showed the highest radical scavenging activities in both ABTS and ORAC assays with Trolox equivalent (TE) values ranging from 0.69 to 4.97 µmol TE/µmol peptide, followed by Cys- and Met-containing dipeptides. With respect to their reducing power and Fe2+ chelating abilities, only Cys-containing dipeptides showed moderate reducing power, and none of them displayed Fe2+chelating ability. It indicated that antioxidant dipeptides mainly acted as radical scavengers and the presence of Tyr, Trp, Cys or Met residue with electron/hydrogen donating ability was the driving force for dipeptides to scavenge radicals. Additionally, Tyr- and Trp-containing dipeptides with Tyr/Trp residue at the N-terminus showed stronger antioxidant activities than that at the C-terminus, and the neighboring residue also affected their activities by steric effect, hydrophobicity and hydrogen bonding among others.
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