In vitro evaluation of antioxidant activity of essential oils and their components

Abstract

Clove and nutmeg essential oils were analysed by GC and GC–MS. These oils, together with 16–18 components found to be present, were tested for antioxidant properties at final concentrations of 0.05–2.5×104 ppm in an egg yolk-based thiobarbituric acid reactive substances (TBARS) assay and also undiluted in a β-carotene agar diffusion assay. Both the essential oils and the components tested in the TBARS assay demonstrated some degree of antioxidant activity. Only the clove oil, the nutmeg oil, eugenol and terpinolene demonstrated any ability to inhibit the oxidative bleaching of the β-carotene agar. The ability of the oil components to inhibit malondialdehyde formation, and therefore lipid peroxidation, in the TBARS assay, yet apparently to possess no activity in the β-carotene agar diffusion assay, demonstrates the importance in the screening of plant material for bioactivity of using a bank of assays in vitro before assigning bioactivities. By using a number of assays, not only should the number of false positives and negatives be greatly reduced, but evidence pertaining to the mechanism of action may be obtained. Copyright © 2000 John Wiley & Sons, Ltd.