Efficient and green ultrasonic-assisted extraction of flavonoids from Sophorae Tonkinensis Radix Et Rhizoma using deep eutectic solvent: Optimization and extraction mechanism

For the advancement of an environmentally friendly and sustainable plant industry, an excellent high-efficiency extraction procedure was exploited for total flavonoids from Sophorae Tonkinensis Radix Et Rhizoma (STRR) based on deep eutectic solvents (DESs) integrated with ultrasonic-assisted extraction (UAE). A comparative study assessed the extraction performance of traditional organic solvents and 17 DESs, with the choline chloride and acrylic acid combination yielding the best results. Optimization through response surface methodology (RSM) achieved a maximum flavonoid yield of 3.785 ± 0.026 mg/g under optimal conditions: 61 min, 65 ℃, solid/liquid ratio 1:148 g/mL, molar ratio 1:4, and 20 % water content. HPLC-MS was employed to quantify the three flavonoids (quercetin, rutin, and formononetin) in the extract, revealing their extraction yield in the DES to be 3.039 ± 0.226 mg/g, 41.274 ± 2.545 mg/g, and 73.926 ± 6.603 mg/g, respectively. These levels are 2–4 times higher than those in the methanol and ethanol extracts. Furthermore, the extraction mechanism was further elaborated with density functional theory (DFT) analysis showing the presence of non-covalent interactions (hydrogen bonding and van der Waals forces) between DES and the samples. The analysis highlighted the excellent extraction performance of DES from multiple aspects and perspectives, including electrostatic potential (ESP), mutual penetration distance (MPD), interaction region indicator (IRI), binding energy, and electrostatic potential quantitative distributions. Thus, the findings of this study demonstrate that DES-UAE represents a highly efficient and environmentally sustainable approach for extracting bioactive compounds from plants, thereby providing valuable support for the development and application of this green extraction technique in the plant industry.