A green approach for the extraction and characterization of oridonin and ursolic and oleanolic acids from Rabdosia rubescens and its kinetic behavior

Abstract

An ultrasound-assisted supercritical carbon dioxide (USC-CO₂) procedure was developed for the extraction of ursolic acid, oleanolic acid and oridonin from Rabdosia rubescens, with yields that were 9.84-10.46 and 15.43-21.10% higher than those of the conventional SC-CO₂ and heat-reflux extractions, respectively. USC-CO₂ uses a shorter extraction time (1.83-2.09 times) and less organic solvent (3.39-173.25 times) to operate at a lower extraction temperature (5-16 °C). The dominant component in the extract was oridonin, which may indicate that the kinetic behavior in the extraction system is predominated by that of oridonin. Furthermore, the USC-CO₂ and conventional SC-CO₂ dynamic extraction kinetics of oridonin from R. rubescens were well described by the second-order rate and Fick's second law models. The extraction rate constant, energy of activation for diffusion, Biot number and thermodynamic parameters were deduced from the data obtained. These results provide valuable insights into the USC-CO₂ and conventional SC-CO₂ procedures.

Keywords: Diffusion model; Oleanolic acid; Oridonin; Rabdosia rubescens; Second-order rate model; Thermodynamic parameters; Ultrasound-assisted supercritical CO(2) extraction; Ursolic acid.