Extraction of curcuminoids and ar-turmerone from turmeric (Curcuma longa L.) using hydrophobic deep eutectic solvents (HDESs) and application as HDES-based microemulsions

The extraction of curcuminoids and aromatic (ar)-turmerone from Curcuma longa L. using organic solvents produces chemical waste, and is therefore incompatible with food applications. To address this issue, this study presents the design of hydrophobic deep eutectic solvents (HDESs) and HDES-based microemulsions. Using the response surface methodology (RSM), the optimal extraction conditions were identified as follows: HDES = OA: menthol (1:3.6 M ratio), solid-to-liquid ratio = 10:1 (mg/mL), and extraction duration = 90 min (prediction accuracy >= 85 %). Under these conditions, the HDES extraction yields of bisdemethoxycurcumin, demethoxycurcumin, curcumin, and ar-turmerone were 2.49 +/- 0.25, 5.61 +/- 0.45, 9.40 +/- 0.86, and 3.83 +/- 0.19 % (w/w, dry basis), respectively, while those obtained using the HDES-based microemulsion were 2.10 +/- 0.18, 6.31 +/- 0.48, 12.6 +/- 1.20, and 2.58 +/- 0.19 % (w/w, dry basis), respectively. The HDES and its microemulsions are more effective and environmentally friendly than conventional organic solvents for the extraction of curcuminoids and ar-turmerone, and these solvents are also compatible with food and pharmaceutical formulations.