Ultrasound-Assisted Extraction of Curcumin Using a Deep Eutectic Solvent: Molecular Insights into the Extraction Mechanism

In this study, five levulinic acid-based deep eutectic solvents (DESs) were evaluated for the ultrasound-assisted extraction of curcuminoids from Curcuma longa. The relationship between DES composition, intermolecular interactions, and extraction performance was investigated by combining extraction experiments with spectroscopic characterization and quantum chemical calculations. The levulinic acid–ethylene glycol system at a 1:2 molar ratio exhibited the best performance, achieving an extraction yield of 99.9 mg·g−1. FTIR and 1H NMR analyses characterized the interactions within the DES, while SEM observations indicated structural disruption of the turmeric matrix after ultrasound treatment. Molecular analyses suggested that hydrogen bonding and van der Waals interactions contributed to the association between the DES and curcuminoids. These results provide molecular insights into the extraction process and a basis for designing greener solvent systems for curcuminoid extraction.