Ultrasound-assisted hydrophobic deep eutectic solvent extraction and purification of ursolic acid and oleanolic acid from Cornus officinalis: Optimization and mechanistic insights

This study aims to address the issues of low extraction efficiency and environmental impact of conventional methods for extracting ursolic acid (UA) and oleanolic acid (OA) from Cornus officinalis fruit. An effective approach for the extraction and purification of UA and OA from Cornus officinalis using a hydrophobic DES (DL-menthol: isopropanol) with good biocompatibility was proposed. Using single-factor and response surface optimization under conditions of a solid: liquid ratio of 1:21 g/mL, ultrasonic treatment of 40 min, power of 300 W, and temperature of 29 °C, the total extraction yield of UA and OA was 9.38 ± 0.17 mg/g, 2.43 times higher than that achieved with 70% ethanol. Subsequent purification with AB-8 macroporous resin showed that the adsorption behavior followed pseudo-second-order kinetics and the Freundlich model. Scanning electron microscopy (SEM) demonstrated that the ultrasonic cavitation disrupted the cell walls of Cornus officinalis, promoting the penetration of DES. Quantum chemical calculations revealed that DES interacts with UA/OA via hydrogen bonds and van der Waals forces, accompanied by a favorable binding energy, elucidating the extraction mechanism. This study provides experimental evidence and technical guidance for the green extraction and purification of the hydrophobic triterpenic acids UA and OA.