Abstract
Oleanolic acid (OA) and ursolic acid (UA) have been considered to be two of the most valuable bioactive compounds in Hedyotis corymbosa and might be responsible for its therapeutic effectiveness. In this study, OA and UA were extracted from this plant with a hyphenated procedure for ultrasound-assisted SC-CO2 (HSC-CO2) extraction at various cosolvent (80% ethanol, v/v) percentages (2.5–15.4%, v/v), extraction times (15–105min), temperatures (33–68°C) and pressures (11.0–32.0MPa). Conventional SC-CO2 extraction was also performed with the aim of comparing the utility of these two extraction techniques for the analysis of the discussed compounds in H. corymbosa samples. It was found that HSC-CO2 extraction had higher yield and efficiency than conventional SC-CO2 extraction. The solubilities of OA and UA in SC-CO2 were further determined at various temperatures and pressures. In addition, the solubility data of OA and UA in SC-CO2 showed a good agreement with the values obtained from the Bartle, Chrastil and modified Kumar and Johnston models. Using the results of these correlation analyses, the total heat of solution and the enthalpies of vaporization and solvation for OA and UA were approximately estimated.
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