Abstract
Essential oils are gaining increasing interest due to their multiple biological activities and great potential for therapeutic use. The antioxidant effect of essential oils is of special interest in diseases with inflammatory aspects. In this paper, the antioxidant activities of eleven essential oils extracted from Australian native plants were examined by the 2,2-diphenyl-1-picryhydrazyl (DPPH) and 2,2′-azinobis (3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) assays. In the DPPH assay, all of the essential oils showed substantial antioxidant potential, with a radical-scavenging activity ranging from 12.9% ± 0.3% to 86.9% ± 0.2% at the concentration of 1.6 × 10−2 mL/mL. In the ABTS assay, lemon-scented tea-tree oil (Leptospermum petersonii Bailey) (80.6% ± 0.7%), Australian blue cypress oil (Callitris intratropica R. T. Baker & H. G. Smith) (78.6% ± 1.3%), lemon-scented eucalyptus oil (Eucalyptus citriodora Hook.) (56.7% ± 0.9%) and lemon-scented ironbark oil (Eucalyptus staigeriana F. Muell. ex Bailey) (58.9% ± 0.8%) exhibited relatively high radical-scavenging activities at the concentration of 1.6 × 10−2 mL/mL. Taken together, in both DPPH and ABTS assays, lemon-scented tea-tree oil (with IC50 of 1.5 × 10−3 mL/mL and 1.5 × 10−3 mL/mL, respectively), Australian blue cypress oil (with IC50 of 9.5 × 10−3 mL/mL and 3.0 × 10−3 mL/mL, respectively), lemon-scented eucalyptus oil (with IC50 of 4.8 × 10−3 mL/mL and 8.9 × 10−3 mL/mL, respectively) and lemon-scented ironbark oil (with IC50 of 6.4 × 10−3 mL/mL and 7.0 × 10−3 mL/mL, respectively) showed the highest antioxidant potential of the essential oils tested. By comparison, the antioxidant capacity of vitamin E had IC50 values of 5.3 × 10−5 mL/mL and 4.3 × 10−6 mL/mL in the DPPH and ABTS tests respectively.