The essential oil from Cymbopogon validus
The chemical and biological properties of the essential oil from Cymbopogon validus were investigated. Hydro-distillation was used to extract the oil from C. validus, the flower-heads, leaves, culms and rhizomes. The percentage oil yields obtained from the plant organs varied from 0.05 to 1.23%, with the greatest concentration found in the flower-heads and rhizomes, 1.23 and 1.12% respectively. A sensory evaluation of the oil revealed that the essential oil was slightly murky, pale yellow in colour, had a strong turpentine-like smell and remained liquid at room temperature. The oxidative stability of C. validus oil was evaluated by determining its Rancimat induction period (negative), peroxide value (60.56 meq/kg), iodine value (84.55), percentage free fatty acids (0.19%) and percentage cholesterol (3.03%). These results indicated that the oil was highly susceptible to oxidation. Chromatographic profiles of the oils from C. validus, as well as the plant organs were generated using gas chromatography-mass spectroscopy (GC-MS). Predominant compounds present in the oil included alpha-Cubebene, Camphene, Geraniol, Limonene, Myrcene, Palmitic acid and Sabinene. C. validus essential oil was also investigated for its antimicrobial (disk diffusion), antioxidant (1, 1-Diphenyl-1-Picrylhydrazyl (DPPH) assay), anti-inflammatory (5-lipoxygenase assay), anti-mosquito properties (insecticidal, larvicidal and repellency assays) and toxicity profile (Brine shrimp and Ames assays). The oil showed poor antimicrobial activity and inhibited the growth of only Gram positive bacteria with a minimum inhibitory concentration (MIC) of 0.0625 (vol/vol) for Bacillus, Micrococcus and Staphylococcus species. The oil also exhibited excellent antioxidant activity, scavenging more than 80% of DPPH free radicals and possesses anti-inflammatory activity (IC50=190 ppm). C. validus oil showed good adulticidal activity (53.7% mortality) and excellent larvicidal (100% mortality) and repellent activity (100% repellency) against Anopheles arabiensis mosquitoes. At high concentrations, the oil was toxic to brine shrimp larvae. However, when diluted it was safe and the minimum inhibitory concentration was 0.0001(vol/vol). The absence of revertant colonies at all essential oil concentrations in the Ames test suggest that the oil is not mutagenic. These results lead the way for exploiting C. validus oil as a multi-functional agent that has antibacterial, anti-oxidant, anti-inflammatory, and anti-mosquito properties.