Ultrasound- and heat-assisted extraction of glycyrrhizin from licorice by two glycerol-based DESs - Modeling and optimization as per response surface methodology

Abstract

Glycyrrhizin is an important bioactive compound of licorice (Glycyrrhiza glabra) having many pharmaceutical properties. The present study explored the extraction of glycyrrhizin from licorice in two glycerol-based deep eutectic solvents glycerol-ammonium acetate (GAA) and glycerol-choline chloride (GCC) and by two different techniques heat-assisted extraction (HAE) and ultrasound-assisted extraction (UAE). For optimization, response surface methodology (RSM) as per CCD (central composite design) was applied. Quantification of the compound was done by HPLC (high performance liquid chromatography). In GAA-HAE, the highest yield 36.96 mg/g was at 80 °C temperature, 25 min time, and 50% DES concentration and in GCC-HAE, the highest yield was 35.26 mg/g that was at temperature 80 °C, time 65 min and 50% DES concentration. In GAA-UAE, the highest yield 35.41 mg/g was at temperature 60 °C, time 79 min and 70% DES concentration, and in GCC-UAE, the highest yield 31.37 mg/g was at temperature 80 °C, time 25 min and 50% DES concentration. UAE-methanol gave the highest yield 31.36 mg/g that was at temperature 60 °C, time 45 min and 70% methanol. The predicted models had high fitness each having a significant p-value (<0.05) and a nonsignificant lack of fit p-value. The R2 values were about 94%, 98%, 93%, 95% and 95% for GAA-UAE, GCC-UAE, GAA-HAE, GCC-HAE and methanol-UAE models, respectively, which also indicated high adequacy of the models. In terms of yield, HAE and UAE were comparable but UAE has the advantage of being more environmentally friendly, and GAA was more powerful than GCC as extracting medium. As a result, GAA-UAE should be a viable option for extracting glycyrrhizin from licorice as an efficient and environmentally friendly method.