This study compared the use of ultrasound-assisted supercritical CO2 (USC-CO2) extraction to obtain apigenin-rich extracts from Scutellaria barbata D. Don with that of conventional supercritical CO2 (SC-CO2) extraction and heat-reflux extraction (HRE), conducted in parallel. This green procedure yielded 20.1% and 31.6% more apigenin than conventional SC-CO2 extraction and HRE, respectively. Moreover, the extraction time required by the USC-CO2 procedure, which used milder conditions, was approximately 1.9 times and 2.4 times shorter than that required by conventional SC-CO2 extraction and HRE, respectively. Furthermore, the theoretical solubility of apigenin in the supercritical fluid system was obtained from the USC-CO2 dynamic extraction curves and was in good agreement with the calculated values for the three empirical density-based models. The second-order kinetics model was further applied to evaluate the kinetics of USC-CO2 extraction. The results demonstrated that the selected model allowed the evaluation of the extraction rate and extent of USC-CO2 extraction.
