Abstract:Six kinds of deep eutectic solvents were designed and prepared, and four extraction techniques, namely, ethanol extraction, freeze-thaw extraction, ultrasonic extraction, and microwave extraction were compared to develop an efficient and environmentally friendly method for extracting flavonoids from Osmanthus fragrans. Ultrasound-assisted extraction using deep eutectic solvents was determined to be the optimal method. The effects of molar ratio of solvents, liquid-to-raw material ratio, water content, ultrasonic power, and extraction time on the yield of flavonoids were investigated through single-factor tests. Based on the results, response surface curves were drawn to obtain the optimal conditions for flavonoid extraction from Osmanthus fragrans. Optimal extraction can be achieved by ultrasound-assisted extraction using a ternary deep eutectic solvent (choline chloride/sorbitol/1,2-propanediol) under the following conditions: liquid-to-raw material ratio, 60:1 (mL/g); choline chloride-to-sorbitol-to-1,2-propanediol ratio, 2:1:4 (mol/mol/mol); water content, 62 mol; ultrasonic power, 150 W; and extraction time, 16 min. Under these conditions, the maximum yield of total flavonoids reaches 10.06 mg/g, which is 8.93 mg/g higher than that achieved using the traditional ethanol extraction method. This proves that ultrasound-assisted extraction using an environmentally friendly deep eutectic solvent is highly efficient. The good agreement between the experimental results and the proposed response surface model indicated the effectiveness of the model. The findings of this study provide a reference for the future utilization of deep eutectic solvents for green extraction from natural products.
