An Improved System to Evaluate Superoxide-Scavenging Effects of Bioflavonoids

The pyrogallol autoxidation method has been widely utilized to evaluate various antioxidants in antioxidative bioactivities. However, this method is generally not appropriate for estimating the ^. O₂^- radical scavenging capacity of bioflavonoids, as it enables bioflavonoids to generate ^. O₂^- radical in oxygen-alkaline (pH 8.2) surroundings. In the present study, an improved DMSO (dimethyl sulfoxide) system (pH 7.25, versus pH 8.2 of the pyrogallol autoxidation) was successfully developed to evaluate the ^. O₂^- radical scavenging capacity of bioflavonoids by EPR technique and using the spin trapping reagent DMPO (5,5-dimethyl-1-pyrroline-N-oxide). The non-protonic environment supplied by the system promotes the stabilization of the ^. O₂^- radical and therefore ensures a much more accurate measurement of ^. O₂^- radical scavenging capacity in bioflavonoids if compared to protonic solvents. The results demonstrated that the effects of scavenging ^. O₂^- radicals in natural bioflavonoids follows the order: dihydromyricetin>myricetin>quercetin>kaempferol>baicalein>chrysin, which are well associated with numbers of hydroxyl groups attached to their molecular skeletons and/or active H of their configurations. Interestingly, the higher superoxide-anion scavenging effect measured for dihydromyricetin with respect to myricetin is possibly attributed to the fact that dihydromyricetin can be transformed into myricetin in the presence of ^. O₂^- radical, resulting from the homolysis of active H donated from C3-H bond of DMY via ^. O₂^- radicals.