The DPPH free-radical scavenging activity of the essential oil was determined according to the method reported by Wang, et al. (2008). 1 ml of different concentrations of the essential oil in methanol (0-5000 µg/ml) was mixed with 2 ml of 610-5 M DPPH solution in methanol. The reaction mixture was well shaken and kept it in the dark at room temperature for 30 min. The absorbance of the reaction mixture was measured at 517 nm against the blank, i.e. methanol. L-ascorbic acid was used as a positive control. The percentage of scavenging DPPH radicals was calculated as follows:
Percent inhibition = [1-(A1-A2)/A0] x 100%
where A0 is the absorbance of the control (without the essential oil), A1 is the absorbance of the reaction mixture and A2 is the absorbance of the sample without DPPH.
The EC50 value, the effective concentration at which the DPPH scavenging effect being 50% was obtained by linear equation from graph plotted between scavenging percentage and essential oil concentration.