2.2.4.5. Superoxide anion radical (O2
−) scavenging ability assay
and inhibition of pyrogallic acid autooxidation. The superoxide
anion radical scavenging capabilities were assayed according
to the method previously described by Zou, Gui, Zhong, and
Zhu (1986) with slight modifications. Briefly, reaction mixtures
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 calculated
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.