Optimization of total alkannin yields of Alkanna tinctoria by using sub- and supercritical carbon dioxide extraction

The effects of supercritical carbondioxide extraction was investigated to compare previously validated extraction methods on total alkannin yield with Alkanna tinctoria collected form Antalya, Turkey. A two-step process was used; extraction of alkannin derivatives with supercritical CO2 followed by alkaline hydrolysis of alkannin derivatives. A Box-Behnken exprerimental design was used to evaluate the effect of three variables, pressure (50–350 bar), temperature (30–80 °C) and CO2 flow (5–20 g min−1) at 1:30 ratio of alkanna root:CO2 amount. Response surface analysis revealed that the data were adequately fitted to a second-order polynomial model with R2 0.9665 and the most effective variable was pressure (P ≤ 0.05). Optimum conditions were determined as 80 °C, 175 bar, 5 g min−1 CO2 flow yielding the highest total alkannins (1.47%) which was higher than conventional hexane extraction (1.24%) providing a solvent-free alternative for industrial production.