Abstract
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 (.) O(2)(-) radical scavenging capacity of bioflavonoids, as it enables bioflavonoids to generate (.) O(2)(-) 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 (.) O(2)(-) 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 (.) O(2)(-) radical and therefore ensures a much more accurate measurement of (.) O(2)(-) radical scavenging capacity in bioflavonoids if compared to protonic solvents. The results demonstrated that the effects of scavenging (.) O(2)(-) 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 (.) O(2)(-) radical, resulting from the homolysis of active H donated from C3-H bond of DMY via (.) O(2)(-) radicals.