A study of the composition and antimicrobial activities of stored and freshly extracted leaf essential oil of Ocimum gratissimum L.

There have been concerns expressed on the biological activities of certain essential oils following long-term storage. The aim of this study was therefore to determine the composition and antimicrobial activities of samples of stored and freshly extracted essential oils of Ocimum gratissimum Linneo (Lamiaceae) in order to provide an exhaustive comparison of these properties in the studied oils. The essential oils were obtained using steam distillation from fresh leaves of O. gratissimum L. collected in Ile-Ife (Nigeria) in the early morning hours in April 2005 and March 2013. These essential oils were then stored in amber coloured bottles in a refrigerator at 4 ºC. GC-MS analyses of the stored and fresh essential oils led to the identification of twelve and five constituents, respectively. The proportions in the stored and fresh essential oils were thymol (46.2 and 76.0%), linalool (14.0 and 7.0%), neral (8.4 and 6.7%), eucalyptol (3.9 and 5.3%), terpinen- 4-ol (1.8 and 2.4%), geranial (11.7 and 0%), α-terpineol (2.1 and 0%) and nerol (1.8 and 0%), respectively. The antibacterial activities of the two essential oils were comparable, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) of which were from 0.25% v/v to 4.0% v/v. On the other hand, the stored essential oils showed higher antifungal effects with MIC and minimum fungicidal concentration (MFC) of 0.0625%v/v against Candida spp. Both essential oils completely killed 1.0 x 10⁸ CFU/ mL bacterial innoculum within three hours. The differences in the antimicrobial activities obtained for the fresh and stored essential oil of O. gratissimum L. were presumably due to different proportion of constituents.