Ionic Liquid-Based Ultrasonic/Microwave-Assisted Extraction of Steroidal Saponins from Dioscorea zingiberensis

Purpose: To develop a more green, efficient and low cost process for the extraction of steroidal saponins from Dioscorea Zingiberensis C. H. Wright. Methods: Six kinds of ionic liquids with different cations and anions were evaluated. In addition, the extraction parameters of the ionic liquid based ultrasonic/microwave extraction were studied. In order to quantify the total saponin content accurately, all steroidal saponins were converted into diosgenin and quantified with an appropriate HPLC procedure. IL-UMAE under optimal conditions was compared with heat reflux extraction (HRE) and ultrasonic assisted extraction (UAE). Results: 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm]BF4) solution at concentration of 0.5 mol L-1 was selected as extraction solvent. The optimum conditions were as follows: solvent to solid ratio 15:1, microwave power 500 W and extraction time 8 min. Under these optimal conditions, the highest extraction yield of diosgenin 10.24 ± 0.31 mg g-1 was obtained. It took only 8 min to obtain the 91.67 % content of diosgenin obtained by traditional HRE. Extracting on time was shortened from 120 min to 8 min. Conclusion: Compared with traditional methods, IL-UMAE method uses Ionic liquid-solvent which greatly shortens the extraction time. IL-UMAE as a simple, effective and environmentally friendly approach shows a broad prospect for active ingredient extraction.