Deep Eutectic Solvent-Based Ultrasonic-Assisted Extraction of Three Antioxidant Flavonoids from Sophorae Fructus: Optimization, Quantification, and Activity Evaluation

• DES-1 (choline chloride/ethylene glycol) combined with ultrasound-assisted extraction (UAE) achieved significantly higher yields (1.5- to 2-fold) of key flavonoids (rutin, genistein, sophoricoside) from Sophorae fructus compared to conventional 70% ethanol. • Response surface methodology established optimal DES-UAE conditions (1:5 molar ratio, 30% water, 35 mL/g, 53 min, 55°C), providing an efficient and environmentally friendly alternative for flavonoid extraction. • The DES-UAE extract demonstrated significantly stronger antioxidant activity in DPPH, ABTS, superoxide anion, and FRAP assays compared to the 70% ethanol extract, highlighting the bioactivity benefits of this extraction method. Sophorae fructus (SF) berries (derived from Styphnolobium japonicum (L.) Schott fruits) contain abundant flavonoids such as sophoricoside, which show antioxidant activity. Here, we combine a deep eutectic solvent (DES) and ultrasonic-assisted extraction to extract flavonoid compounds from SF. Six DESs prepared by combining choline chloride (hydrogen bond acceptor) and polyols (hydrogen bond donors) have been screened and compared with 70% ethanol solvent. Optimal conditions for SF flavonoid extraction using DESs are assessed through single-factor experiments and the response surface methodology approach. The contents of three flavonoid components, namely rutin, genistein, and sophoricoside, in SF are quantified by high-performance liquid chromatography-diode array detector. The antioxidant activity of the extracted SF flavonoids is confirmed through different assays. Among all DESs, DES-1 (choline chloride/ethylene glycol) shows the highest extraction rate, and this rate is remarkably higher than that of the 70% ethanol solvent. After process standardization, the following optimal conditions are obtained: molar ratio, 1:5; water content, 30%; liquid-to-solid ratio, 35 mL/g; ultrasonication time, 53 min; and ultrasonication temperature, 55°C. By using these experimental settings, we obtain the following highest extraction rates for rutin, genistein, and sophoricoside: 2.20% ± 0.067%, 0.53% ± 0.010%, and 14.46% ± 0.227%, respectively; these rates are 1.5- to 2-fold higher than those achieved using the 70% ethanol solvent. Moreover, the DES-UAE-derived extract shows stronger antioxidant activity than the 70% ethanol extract. The antioxidant activity levels of the DES-UAE-derived extract quantified by DPPH, ABTS, superoxide anion, and FRAP assays are 60.71%, 100%, 99.59%, and 200.77 μmol/mL, respectively, which are higher than those of the 70% ethanol extract (52.76%, 92.45%, 87.25%, and 185.73 μmol/mL, respectively) measured by these methods. Thus, this study reports an efficient and ecofriendly process for extracting SF flavonoids, facilitating the development of innovative treatment approaches by utilizing natural plant products.