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 oil of Ocimum gratissimum Linneo (Lamiaceae) in order to provide comparison of these properties in the oils. The essential oils were obtained from steam distillation of fresh leaves of O. gratissimum 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 bottle in a refrigerator at 4 oC. GC-MS analyses of the stored and fresh essential oils identified twelve and five constituents respectively. The proportions in the stored and fresh essential oils were: thymol (46.2 and 76.0%, respectively), 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%). 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 oil 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 108cfu/ml bacterial innoculum within three hours. The differences in the antimicrobial activities obtained for the fresh and stored essential oil of O. gratissimum were presumably due to different proportion of constituents.