Effect of extraction techniques on the chemical composition and antioxidant activity of Eucalyptus camaldulensis var. brevirostris leaf oils

The volatile oil compositions of Eucalyptus camaldulensis var. brevirostris leaves obtained by hydrodistillation (HD) and supercritical fluid extraction methods (SFE) were analysed qualitatively and quantitatively by GLC-MS. Ninety different components were separated and most of them identified. In both extracts the main constituents were found to be beta-phellandrene (8.94 and 4.09\%), p-cymene (24.01 and 10.61\%), cryptone (12.71 and 9.82\%) and spathulenol (14.43 and 13.14\%). The yield of the monoterpene hydrocarbons in HD oil (0.288 g/100 g fresh leaves) was slightly higher compared with that in the SFE extract (0.242 g/100 g fresh leaves). The SFE extract possessed higher concentrations of the sesquiterpenes, light oxygenated compounds and heavy oxygenated compounds than the HD oil. The relationship between the antioxidant activity and chemical composition of the extracted oils was investigated. The significant amounts of p-cymen-7-ol and thymol are responsible for the antioxidative activity of both extracts. The concentration of both compounds, but especially that of p-cymen-7-ol (2.25\%), is higher in the SFE extract. This corresponds with the higher antioxidative activity of the SFE compared with the HD extract. p-Cymen-7-ol, a compound newly identified in leaves of Eucalyptus species, exhibited superior antioxidant activity in comparison with that of butylated hydroxyanisole.