Comparative study of the alkyl and peroxy radical scavenging activities of polyphenols

The lipid antioxidative activities of polyphenols with high oxygen radical capacities need to be measured at low oxygen tensions. In this study, differences in the reactivity of catechins and resveratrols towards alkyl (R) and peroxy (PhCOO) radicals were observed at lower oxygen pressures. The radical scavenging activities for catechin, epicatechin, resveratrol and n-propyl gallate with or without 2-mercapto-1-methylimidazole (MMI), a thiol were investigated by differential scanning calorimetry (DSC) monitoring of the polymerization of methyl methacrylates (MMA) initiated by 2,2′-azobisisobutyronitrile (AIBN, an R radical) or benzoyl peroxide (BPO, an PhCOO radical) at 70 °C under nearly anaerobic conditions. Catechin, epicatechin and resveratrol with MMI, but not n-propyl gallate showed the less length of induction period than that for corresponding ones without MMI, probably resulting from the reaction of MMI radicals with molecular oxygen in the system. Also, the inhibitory rate of propagation (Rinh) for catechin and resveratrol in the BPO system was much more greater than that in the AIBN system. The reactivity of catechins and resveratrol with R or PhCOO radical was considerably different, whereas n-propyl gallate did not different between radicals under nearly anaerobic conditions.