2.5. Extraction procedure

For DES-based UAE of GLA and ISL, powdered licorice root (0.5 g) was added to 10 mL of DESs in the tube. Then DES-based UAE was performed in an ultrasonic bath (Scientz, SB-5200DTD, Ningbo, China) at the ultrasonic power of 480 W. After extraction for 20 min at 55 °C, the samples were centrifuged (12000 rpm, 10 min), and the collected supernatant was used for HPLC analysis. In comparison, UAE using water and methanol as solvent were also carried out under the same parameter as that of DES-based UAE. The DESs prepared were shown in Table 1.

Based on the results of DES-based UAE, DES with optimal extraction efficacy (ChLa) was selected for further solvent screening. The effect of the molar ratio of HBA and HBD (1: 1, 1: 2, 1: 3, 1: 4, 1: 5, and 1: 6) and water content (0, 20, 40, 60, 80, and 100 %) on the extraction efficacy of selected DES were evaluated. The sonication input power and centrifugation procedures were the same as described above. Each extraction procedure was performed in triplicate.