Extraction and purification of triterpenoid saponins from licorice by ionic liquid based extraction combined with in situ alkaline aqueous biphasic systems

Triterpenoid saponins in licorice are important lead compounds for nutraceutical and pharmaceutical applications. This study developed a novel method for extraction and purification of triterpenoid saponins from licorice by ionic liquid based ultrasonic-assisted extraction combined with in situ alkaline aqueous biphasic systems (IL-UAE-AABS). IL-UAE was firstly used to efficiently extract triterpenoid saponins from licorice, which were further purified using in situ IL-AABS formed by adding NaOH into the extraction solution. We screened out the best-performing IL, namely 1-butyl-3-methylimidazolium tetrafluoroborate ([C4MIM]BF4), from various ILs able to form AABS with NaOH, and established the optimal conditions (extraction time, [C4MIM]BF4 concentration and solvent to solid ratio for IL-UAE, and NaOH concentration and temperature for IL-AABS). The established method could achieve high extraction efficiency (26.0 mg/g for glycyrrhizin) and total purify (more than 81.5%) for triterpenoid saponins, which was far superior to conventional IL-ABS. In addition, [C4MIM]BF4 could be easily recovered and reused for the IL-UAE-AABS process for at least three times without apparent worse performance. This is the first report on extraction and purification of natural products by IL-UAE-AABS, which was shown to be able to efficiently and selectively obtain triterpenoid saponins from herbal medicines with good prospects.