Volatile Constituents and Antioxidant Activity of Essential Oils Obtained from Important Aromatic Plants of Ethiopia

The essential oil composition of the leaves of Rosmarinus officinalis L. and Lippia adoensis Hochst. var. koseret Sebsebe, the leaf and stem of Foeniculum vulgare Miller, and the seeds of Coriandrum sativum L. were analyzed by GC and GC-MS. The antioxidant activity of the EOs was also examined. Hydrodistillation of leaves of F. vulgare yielded an essential oil lighter than water (0.09%), and a heavy oil fraction (0.48%), while stems gave 0.09% of EO. The percentage yield of EO from the leaves of R. officinalis and L. adoensis was 0.33% and 0.19%, respectively. The seeds of C. sativum gave an EO yield of 0.46%. A total of 18 (99.93%) and 53 (99.51%) compounds were detected from the light and heavy oils of the leaves of F. vulgare, respectively. The light leaf oil of F. vulgare was found to contain mainly aromatic compounds while the heavier oil was found to be rich in monoterpenoids. F. vulgare stem EO was observed to contain 20 (99.83%) compounds which were mostly similar to the ones in the light leaf oil. Major component of the light and heavy leaf and stem EO was estragole. The heavy leaf EO of F. vulgare also exhibited high levels of limonene. EO from the seeds of C. sativum and the leaves of L. adoensis and R. officinalis showed the presence of 31 (99.76%), 28 (98.43%) and 59 (97.46%) compounds, respectively. Linalool was observed to be the main constituent in C. sativum and L. adoensis EOs. The main constituent in R. officinalis EO was α-pinene followed by 1,8-cineol and camphor in a 4:2:1 ratio. The oils showed relatively weak antioxidant activity examined by the DPPH assay method, with highest activity detected in L. adoensis var. koseret.