High-Efficiency Extraction of Flavonoids from Flos Sophorae Immaturus Using Ultrasound-Assisted Deep Eutectic Solvent: Optimization and Antioxidant Activity

In this study, a novel and efficient method was developed for the extraction of total flavonoids from Flos Sophorae Immaturus (FSI) using ultrasound-assisted deep eutectic solvent (UAE-DES). Different DES formulations were first investigated and choline chloride/1,2-propanediol (ChCl/PD) was identified as the optimal solvent due to its highest flavonoid yield. The extraction process was optimized through single factor experiments and response surface methodology (RSM). An extraction temperature of 68 °C, a sonication time of 41 minutes, a water content of 21% and a liquid-solid ratio of 21 mL/g were identified as the optimal conditions. Under these conditions, a maximum flavonoid yield of 378.77 mg RE/g DW was achieved. The crude extract was further purified using a macroporous D-101 resin, resulting in a flavonoid extract with a purity of 83.11 ± 3.54%. The antioxidant activity of the purified extract (FSPE) was evaluated using DPPH and ABTS radical scavenging assays, showing significant antioxidant properties with IC50 values of 52.50 μg/mL and 49.47 μg/mL, respectively. The UAE-DES method developed in this study not only significantly improves the extraction yield of flavonoids from FSI, but is also in line with sustainable and environmentally friendly practices. This method offers an environmentally friendly, efficient and scalable approach for the extraction of bioactive compounds from medicinal plants and has potential applications in the food, pharmaceutical and dietary supplement industries.