Ultrasonic-assisted pH-responsive deep eutectic solvent extraction of liquiritin and glycyrrhizic acid from licorice: Process optimization, solubilization mechanism, and circulation recovery study

A green ultrasonic-assisted pH-responsive deep eutectic solvent (PDES) extraction strategy was developed for efficient recovery of liquiritin and glycyrrhizic acid from licorice. Menthol/decanoic acid was selected as the optimal solvent. Its formulation and physicochemical properties were systematically characterized, and its environmental performance was evaluated. The optimization of extraction parameters was achieved by response surface methodology. Compared with 70% ethanol, the extraction yields of liquiritin and glycyrrhizic acid were increased by 2.24-fold and 1.44-fold, respectively. Quantum chemical calculations revealed the hydrogen-bonding interaction between PDES and the target compounds. Kinetic and thermodynamic models were employed to fit the extraction data. Recovering PDES through pH adjustment enabled its reuse and sustained the process. This method not only gave high extraction yields but also shed light on the molecular driving forces. Both the recyclability of the solvent and the results from environmental metrics supported the system’s green credentials.