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Radical scavenging activity (%) = [(A0-A1/ A0)* 100]

Hydroxyl radical scavenging activity (HRSA) of the extractives was determined by the method of Klein et al. [30] with a slight modification. 0.5 ml of extractives/standard at different concentration was taken in test tubes. 1 ml of Fe-EDTA solution (0.13% ferrous ammonium sulphate and 0.26% EDTA), 0.5 ml of 0.018% EDTA solution, 1 ml of 0.85% DMSO solution and 0.5 ml of 22% ascorbic acid were added into the test tubes. The test tubes were capped tightly and warm at 85°C for 15 minutes into the water bath. After incubation, the test tubes were uncapped and 0.5 ml ice cold TCA (17.5%) was added to each of test tubes immediately. 3 ml of nash reagent (7.5 gm of ammonium acetate, 300 μl glacial acetic acid and 200 μl acetyl acetone were mixed and made up to 100 ml) was added to all the tubes and incubated at RT for 15 minutes. Absorbance was taken in UV-spectrophotometer at 412 nm wave length. Percentage hydroxyl radical scavenging (% HRSA) activity was calculated using the following equation,

Where A0 is the absorbance of the control, and A1 is the absorbance of the extractives/standard.

Then % of inhibition was plotted against concentration, and from the graph IC50 was calculated.