A new method using ESR spin trapping was proposed for measuring scavenging activity of antioxidants to the hydroxyl (OH) radical. (-)-epigallocatechin gallate (EGCg) and 5,5-dimethyl-1-pyrroline N-oxide (DMPO) were used as an antoxidant and a spin trapping agent, respectively. Conventional method using a Fenton reaction had somedefects on the estimation of the activity, because antioxidant disturbed the generating system of OH radical besides it scavenged the spin adduct (DMPO-OH). This method used intense #gamma#-irradiation as OH radical generating system, and the intensity decrease of DMPO-OH after the end of the irradiation was followed to obtain the rate constant of the scavenging of DMPO-OH with EGCg and to estimate the quantity of DMPO-Oh formed during #gamma#-irradiation. By using these values, the reaction rate constant between Oh radical and EGCg was calculated as a ratio to that of DMPO. It was shown that this method is useful to compare precisely the OH radical scavenging activity of various antioxidants.
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