Optimization of the supercritical fluid extraction of triterpenic acids from Eucalyptus globulus bark using experimental design

The supercritical CO2 extraction of E. globulus deciduous bark was carried out at different temperatures (40–60 °C), pressures (100–200 bar), and ethanol contents (0.0–5.0 wt. %) to study triterpenic acids (TTAs) recovery. A factorial design of experiments and response surface methodology were implemented to analyze the influence of these variables upon extraction and perform its optimization. The best conditions were 200 bar, 40 °C and 5% ethanol, for which the statistically validated regression models provided: extraction yield of 1.2% (wt.), TTAs concentration of 50%, which corresponds to TTAs yield of 5.1 g/kg of bark and a recovery of 79.2% in comparison to the Soxhlet value. The trends of the free and acetylated TTAs were very different, due to their distinct CO2-philic character caused by dissimilar polarities: the acetyl derivatives approached a plateau near 200 bar and 5% ethanol, while the free TTAs extraction always increased in the range of conditions studied.