DPPH radical scavenging assay

DPPH assay was carried out following the modified method of Ajileye et al., [25]. Briefly, the solution of DPPH (0.135 mM) was prepared in methanol and incubated in the dark for 30 min. One hundred microliter of the essential oil or standards (positive control) were prepared in methanol of various concentration ranging from (0.03–0.5 mg/mL), and was added into all the wells of microtiter plate starting from (C-H) in triplicates except for A (A1-A12) and B (B1-B12). Thereafter, 100 μL of 0.135 mM of DPPH solution prepared in methanol was added into the wells from C-H. Absorbance was spectrophotometrically observed at 517 nm and the essential oil ability to lower DPPH to neutral molecule was expressed as percentage inhibition using the formula percentage inhibition = {(Abs _control –Abs _sample)}/ (Abs control) × 100.