Possible chemical mechanisms for the antioxidative activities of peptides include (1) direct oxidation of their amino acid residues (especially Lys, Arg, Thr and Pro) leading to carbonyl formation, (2) direct electron donation especially by the sulphydryl group of Cys residues to quench free radicals leading to loss of peptide sulphydryl group, (3) radical scavenging and oxidative cleavage of peptides through the α-amidation pathway, and (4) prooxidant transition metal chelation