Optimization of the supercritical fluid extraction of Quercus cerris cork towards extraction yield and selectivity to friedelin

Optimization of the supercritical fluid extraction of Quercus cerris cork was carried out using Box-Behnken design of experiments and response surface methodology (RSM). The optimized process variables were temperature (T: 40, 50 and 60 degrees C), ethanol content (EtOH: 0.0, 2.5 and 5.0 wt%) and CO2 flow rate (Q(CO2): 5, 8 and 11 g min(-1)). The studied responses were total extraction yield (eta(Total)), friedelin concentration of the extract (C-Friedelin), and selectivity towards friedelin (alpha(F,nF)). The linear effect of EtOH was by far the most influent operating condition (Pareto analysis) and the highest yield (eta(Total) = 2.2 wt%) was attained with 5.0 wt% EtOH. The RSM model estimates maximum friedelin concentration in the extracts (38.2 wt%) to occur without cosolvent (0 wt% EtOH) for the lowest T (40 degrees C) and Q(CO2) (5 g(CO2) min(-1)). As for selectivity, the experimental alpha(F,nF) values were always higher than 1.0 and reached 3.1 (at 50 degrees C, 5 wt% EtOH, 11 g(CO2) min(-1)). Altogether, these results suggest friedelin can be selectively removed from Quercus cerris cork by supercritical fluid extraction within the range of experimental conditions studied.