Antioxidant activity of (+)-catechin. Rate constant for hydrogen-atom transfer to peroxyl radicals

(+)-Catechin reduced the oxygen consumption rate of a peroxidizing methyl linoleate solution in the hydrogen-bond-accepting solvent tert-butanol, as measured by oximetry (ESR signal linewidth). In contrast to alpha -tocopherol, no induction period was seen for (+)-catechin. The rate constant for hydrogen-atom transfer from (+)-catechin to lipid peroxyl radicals was determined to be k(inh)= (1.45 +/-0.20).10(4) M-1 s(-1) at 50 degreesC, a value smaller by a factor of 40 compared to alpha -tocopherol, but comparable to the same rate constant for synthetic antioxidants and quercetin and the epimeric epicatechin.