Ultrasound-enzyme-assisted extraction of flavonols from <i>Polygonatum odoratum</i> using ternary natural deep eutectic solvents

Natural deep eutectic solvents (NADESs) are emerging green solvents that show great potential in extracting natural products from natural resources. In this study, a third component was introduced into the NADES system, and the screened ternary NADES (choline chloride/fructose/citric acid, 1 : 1 : 2) was combined with ultrasound-enzyme-assisted extraction to extract flavonols from <i>Polygonatum odoratum</i>. The main flavonol components, including quercetin, kaempferol and isorhamnetin, were determined by high-performance liquid chromatography and analyzed in comparison with the extraction efficiency of traditional procedures. The results of Fourier transform infrared spectroscopy and Raman spectroscopy showed that the alteration of intermolecular forces in NADESs promoted the formation of hydrogen bonds between them and flavonols, which significantly increased the extraction yields. After optimization by single-factor and Box-Behnken experiments, the ternary NADES extraction yields could reach 0.24 mg g^-1 under the optimal conditions of cellulase dosage 1.1%, ultrasonic time 62 min, ultrasonic temperature 61 °C, and water content 60%. The study provides an efficient and environmentally friendly way to extract flavonols from natural medicinal plants, and also elucidates the potential mechanism of the ultrasound-enzyme-assisted ternary NADESs for the improved extraction efficiency.