[Process optimization, mechanism exploration, and antioxidant activity study of green extraction of flavonoids from Pueraria lobata flower by ultrasound-assisted deep eutectic solvent].

In this study, an ultrasound-assisted deep eutectic solvent extraction(DES-UAE) technology was established for the green and efficient extraction of flavonoids from Pueraria lobata flower. The optimal solvent system was screened by preparing 12 kinds of deep eutectic solvents(DES). The extraction process was optimized by single factor test combined with the response surface method, and the antioxidant activity of the extract was evaluated. The optimal DES, choline chloride-lactic acid(ChCl-Lac), was characterized by Fourier transform infrared spectroscopy(FTIR) and thermogravimetric analysis(TGA). The extraction mechanism of DES-UAE was discussed by scanning electron microscopy(SEM) and σ profile analysis. At the same time, green evaluation systems of AGREE, AGREEprep, GAPI, and SPMS were used to evaluate the greenness and environmental friendliness of the method. The results show that the optimal DES is ChCl-Lac. The optimal extraction conditions are ultrasonic temperature of 70 ℃, ultrasonic time of 30 min, liquid-solid ratio of 50 mL·g~(-1), water content of 40%, and ultrasonic power of 60 W. Under these conditions, the yields of kakkalide and tectoridin are 1.22 times and 1.26 times higher than those of 70% ethanol extraction, respectively, and the antioxidant activity of the extract is significantly better than that of the 70% ethanol group. Mechanism studies show that ChCl-Lac mainly interacts with flavonoids through hydrogen bonds and van der Waals forces, thereby promoting the dissolution of the target components. The green evaluation results verify the environmental friendliness and sustainability of the method. This study provides a new technical reference for the green and efficient extraction of active ingredients from natural medicinal plants.