Antioxidant synergy and regeneration effect of quercetin, (-)-epicatechin, and (+)-catechin on α-tocopherol in homogeneous solutions of peroxidating methyl linoleate

Antioxidant interactions between flavonoids and a-tocopherol have been demonstrated by oximetry (oxygen concentration measured by ESR signal line width). In tert-butyl alcohol,a,solvent in which flavonoids are weak retarders of peroxidation of methyl linoleate when initiated by alpha,alpha'-azoisobutyronitrile, quercetin and (-)-epicatechin were found to act synergistically with the, chain-breaking . antioxidant alpha-tocopherol. In chlorobenzene, a solvent in which flavonoids are chain-breaking antioxidants, quercetin and (+)-catechin each, regenerated alpha-tocopherol, resulting in a co-antioxidant effect. The stoichiometric,factor of the flavonoids as chain-breaking antioxidants in 1:1 mixtures with alpha-tocopherol Was measured to be close to 1 for quercetin and slightly smaller for the catechins: The apparent inhibition rate,constant, k(inh), for the mixture quercetin/alpha-tocopherol was measured to be 14.1 x 10(5) and 2.6 x 10(6) M-1 s(-1) in tent-butyl alcohol and chlorobenzene, respectively, at 50degreesC. A k(inh) of 4.4 x 10(5) M-1 s(-1) was measured for (+)-catechin alone in chlorobenzene at 50 degreesC.