Near-critical extraction of β-sitosterol and scopoletin from stinging nettle roots

β-Sitosterol (22,23-dihydrostigmasterol) and scopoletin (7-hydroxy-6-methoxycoumarin) were extracted from roots of stinging nettle ( Urtica dioica L.) with supercritical and liquid CO 2 . Extraction rates were measured for both oleoresin and the individual substances in dependence on extraction conditions. The solvent modified with ethanol (0–9.4 wt.%) was applied at the pressures of 100, 200, 250 and 280 bar and the temperatures of 25, 40 and 60 °C. Extracts were analysed by means of HPLC method. The maximum yields of β-sitosterol and scopoletin were 0.63 and 0.058 mg/g dry mass, respectively. In comparison with the extract obtained with diethyl ether, the maximum yields obtained with CO 2 were at least two times higher for both investigated substances. A model describing the extraction of a solute that is present in two forms, free and interacting with matrix, was applied to interpret the experimental extraction curves.