Superoxide anion radical (O2−) scavenging ability assay and inhibition of pyrogallic acid autooxidation. The superox- ide anion radical scavenging capabilities were assayed according to the method previously described by Zou, Gui, Zhong, and Zhu (1986) with slight modifications. Briefly, reaction mix- tures containing Tris–HCl buffer (4.50 mL, 50 mM, pH 8.2) and the test compounds (1.0 mL, 2.4 mg/mL) were incubated at 25 °C for 10 min, and 0.3 mL of pyrogallic acid (3 mM, prepared in 8 mM HCl) was then added. The absorbance of the reaction mixture at 325 nm was then measured at 30-s intervals. The autooxidation rate constant (Kb) of pyrogallic acid was calcu- lated from the curve of A325nm as a function of time. The negative control was pure distilled water, and the positive controls were Vc and BHT. The test compounds’ abilities to inhibit autooxidation are indicative of their O2·− scavenging abilities