Natural deep eutectic solvents as tailored and sustainable media for the extraction of five compounds from compound liquorice tablets and their comparison with conventional organic solvents

Abstract

An efficient and environmentally friendly ultrasound-assisted (UAE) natural deep eutectic solvent (NADES) extraction method was applied for the extraction of five bioactive compounds (liquiritin, isoliquiritin, liquiritigenin, glycyrrhizic acid and isoliquiritigenin) from compound liquorice tablets (CPLTs), and the antioxidant activities of these compounds were evaluated. In this study, eighteen different NADES systems based on either two or three components were tested and a 1,4-butanediol–levulinic acid system (1 : 3 molar ratio) was selected as a topgallant solvent for maximizing analyte extraction yields. Various extraction parameters, such as water content, liquid/solid ratio, extraction time and temperature, were systematically optimized by single-factor and response surface methodology (RSM) experiments. The results indicated that the optimum extraction conditions for the analytes featured a water content of 17%, a liquid/solid ratio of 42 mL g⁻¹ and an extraction time of 30 min. The extracted amounts of liquiritin, isoliquiritin, liquiritigenin, glycyrrhizic acid and isoliquiritigenin reached 5.60, 3.17, 1.27, 74.62 and 1.34 mg g⁻¹, respectively, under optimized conditions, which were much higher than those extracted using conventional organic solvents. In addition, antioxidant tests revealed that the NADES extracts showed higher DPPH and hydroxyl radical-scavenging capacity than the conventional solvent extracts used for comparison. This study provides a suitable approach for efficiently extracting the bioactive compounds of CPLTs. Meanwhile, NADESs can be extended to other natural products as green extraction media.