Chemical composition, In vitro antimicrobial and antioxidant activities of the essential oils of Ocimum gratissimum, O. sanctum and their major constituents

The essential oils of the flowering aerial parts of two Ocimum species viz., Ocimum gratissimum and O. sanctum were analyzed by gas chromatography and gas chromatography/mass spectroscopy. The principal constituent of O. gratissimum and O. sanctum was eugenol (75.1%) and methyl eugenol (92.4%), comprising 99.3 and 98.9% of the total oils, respectively. In vitro antimicrobial activity of the essential oils of O. gratissimum, O. sanctum and their major compounds eugenol and methyl eugenol were screened by using tube dilution methods. O. gratissimum oil was found highly active against S. marcescens while O. sanctum oil showed significant activity against A. niger and S. faecalis. Methyl eugenol exhibited significant activity against P. aeruginosa while eugenol was effective only against S. aureus. Antioxidant activity of oils, eugenol, and methyl eugenol was determined by 2,2-diphenyl-1-picrylhydrazyl and 2,2'- azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) assays. Essential oil of O. gratissimum showed comparative antioxidant activity with IC50 values 23.66±0.55 and 23.91±0.49 μg/ml in 2,2-diphenyl-1-picrylhydrazyl and 2,2'- azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) models, respectively. Eugenol showed slightly weaker antioxidant activity compared to oil of O. gratissimum, while O. sanctum oil demonstrated very feeble antioxidant activity and methyl eugenol did not show any activity. Eugenol and methyl eugenol would be elite source from O. gratissimum and O. sanctum, respectively, of this region could be consider as a source of natural food antioxidant, preservatives, and as an antiseptic.