Natural Hydrophobic Deep Eutectic Solvent for Highly Efficient Extraction of Curcuminoids Assisted by Pulsed Ultrasound: Experimental and Mechanistic Insights

Curcuminoids make up a class of valuable natural pigments, and their green and efficient extraction has always been a challenging task. This study synthesized hydrophobic deep eutectic solvents (HDESs) from natural anisyl alcohol and saturated fatty acids. With the assistance of pulsed ultrasound, these green HDESs efficiently extracted curcuminoids from the plant Curcuma longa L. The extraction parameters were optimized using single-factor experiments and response surface methodology (RSM). The optimal extraction conditions were obtained as follows: a molar ratio of anisyl alcohol to n-nonanoic acid of 1:2, a liquid–solid ratio of 21.58 mL·g–1, an extraction temperature of 25 °C, an ultrasonic time of 25 min, and an extraction time of 60 min. Under these conditions, the extracted curcuminoids amount reached 115.64 mg·g–1 in a single extraction process, outperforming the traditional solvent methanol. The sustainable extraction of curcuminoids by HDES was shown to be as high as 743 mg·g–1 through sequential extraction. Quantum chemical calculations and molecular dynamics simulations investigated the interactions between HDES and curcuminoids during extraction. This work presents a natural green HDES that can replace traditional organic solvents for the efficient extraction of curcuminoids, further promoting the application of green solvents in natural product extraction.