Ultrasound-assisted deep eutectic solvent extraction of echinacoside and oleuropein from Syringa pubescens Turcz.

In this work, deep eutectic solvents (DESs) were synthesized using ultrasound-assisted and stirring heating methods. DES combined with ultrasonic-assisted extraction (UAE) was proposed for the efficient extraction of glycosides from Syringa pubescens Turcz. A series of DES systems were used to evaluate the extraction efficiency of glycosides in S. pubescens . The DES composed of choline chloride/glycerol extracted higher than those of conventional solvents and other DESs. The extraction procedure of DES-UAE was optimized using response surface methodology. The extraction solvent was choline chloride-glycerol formed a DES with the mole ratio of 1:2 with 20 % of water content. The optimum conditions for echinacoside (ECH) and oleuropein (OLE) were ultrasound power of 200 W, extraction temperature of 68 °C, solvent to solid ratio of 20:1 mL/g and the extraction time of 45 min. Furthermore, the DES with 30 % water content can be used as dilution solvent before HPLC analysis of DES extract. In addition, the enrichment of ECH and OLE from DES extract was achieved using HPD-450 macroporous resin, with the recoveries of 80.04 % and 86.21 %, respectively.