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 CO2. 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 CO2 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.