2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay

The radical scavenging activity of the samples were estimated using 2,2-diphenyl-2-picrylhydrazyl (DPPH) assay²¹. Briefly, the methanol solution of the hexane extract was serially diluted with 0.004% DPPH in methanol to furnish 200, 100, 50, and 25 µg/mL of the extract. After 30 min incubation in an oven at 37 °C, absorbance at 517 nm was measured using UV–Vis spectrophotometer. Ascorbic acid and 0.004% DPPH in methanol were used as positive control and blank, respectively. The percentage inhibition of the extracts was calculated using the following formula. % Inhibition = (A_control − A_extract)/A_control × 100 where Acontrol is the absorbance of 0.004% DPPH in methanol and Aextract is the absorbance of DPPH solution plus sample. The DPPH radical scavenging activity of the samples was also expressed as IC₅₀, the concentration of the test compound to give a 50% decrease of the absorbance from that of the control solution. The radical scavenging activity of the other extracts and the isolated compounds of the leaves and the roots of O. cufodontii were also evaluated following the same. Ascorbic acid and quercetin were used as positive controls.