Essential Oil Composition, Antibacterial and Antioxidant Activities of Four Mentha Species Growing in Ethiopia

The essential oils obtained by hydrodistillation from the leaves of Mentha arvensis L., M. longifolia L., M. piperita L., and M. spicata L., were analyzed by gas chromatography (GC-FID) and gas chromatography/ mass spectrometry (GC/MS). In addition, the antibacterial activities of the oils were evaluated against 20 bacterial strains and their radical scavenging potentials were determined in 2,2-diphenyl-1-picrylhydrazyl (DPPH) and deoxyribose degradation assays. Oxygenated monoterpenes were found to be major constituents of all the oils. The essential oil of M. spicata exhibited a significant wide spectrum antibacterial activity against all test strains including multiresistant strains of Pseudomonas aeruginosa and Escherichia coli. The essential oil of M. piperita displayed powerful in vitro radical scavenging activities in both DPPH and deoxyribose degradation assays, with IC50 values of 5.96 μl/ml and 0.57 μl/ml, respectively. The other essential oils also produced concentraion dependant radical scavenging activities with IC50 values ranging between 5.96 and 37.01 μl/ml, and 0.57 and 3.88 μl/ml, in DPPH and deoxyribose degradation assays, respectively. The present study revealed that all the essential oils have the potential to be used as naturally occurring antibacterial and antioxidant agents. Keywords: essential oils, Mentha spp, capillary gas chromatography-mass spectrometry, radical scavenging activity, antibacterial activityEthiopian Pharmaceutical Journal Vol. 25 (2) 2007: pp. 91-10