Evaluation of antioxidant activity of vetiver (Vetiveria zizanioides L.) oil and identification of its antioxidant constituents

Antioxidant capacities of vetiver (Vetiveria zizanioides) oil were evaluated by two different in vitro assays: the DPPH, free radical scavenging assay and the Fe2+-metal chelating assay. Results showed that the vetiver oil (VO) possessed a strong free radical scavenging activity when compared to standard antioxidants such as butylated hydroxytoluene (BHT) and a-tocopherol. However, its metal chelating capacity was relatively weak. VO (10 mu L/mL) dissolved in methanol exhibited similar to 93% free radical scavenging activity in the DPPH, assay and similar to 34% Fe2+ chelating activity in the metal chelating assay. By contrast, 10 mM BHT and 0.1 mM a-tocopherol exhibited 93 and 89% free radical scavenging activities in the DPPH, assay, respectively, and 1 mM EDTA exhibited similar to 97% activity in the metal chelating assay. Among the complex constituents in the crude VO, beta-vetivenene, beta-vetivone, and alpha-vetivone, which had shown strong antioxidant activities, were isolated and identified using various chromatographic techniques including silica gel open column chromatography, silica HPLC, and GCMS. These results show that VO and some of its inherent components can be potential alternative natural antioxidants.