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

•Three bioactive compounds were effectively extracted from Rabdosia rubescens.•Ultrasound-assisted supercritical CO2 extraction can well replace traditional method.•The extraction curve of oridonin was well described by kinetic and diffusion models.•The kinetic parameters provide a good description of the efficiency of the procedure.•The diffusion model further provides good insight into the different procedures. 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.