Extraction of pharmaceutically important curcuminoid platform molecules has been achieved from turmeric with ultrasound-assisted greener solvent extraction, demonstrating excellent performance and product recovery. Extraction of curcuminoids from turmeric was undertaken with both conventional and potentially bio-based solvents. Sustainable solvents, namely, ethyl acetate, ethanol, Cyrene, and deep eutectic solvent (DES-B5, 1:6 ChCl:1,4-butanediol) demonstrated high extraction yields of curcuminoids, including 24.36 ± 3.10, 25.30 ± 4.58, 23.51 ± 2.56, and 27.40 ± 3.80 mg/g of curcumin, respectively. In contrast, curcumin extracted in lower polarity solvents such as hexane, toluene, and tetramethyloxolane was low at less than 7.0 mg/g, whereas 2-MeTHF, DMF, and THF represented moderate extraction yields of 13.80 ± 3.90, 14.43 ± 4.46, and 15.17 ± 2.08 mg/g, respectively. DES-B5 with 10% water extracted the greatest yield of curcumin (46.70 ± 0.55 mg/g), bisdemethoxycurcumin (46.14 ± 0.82 mg/g), and demethoxycurcumin (10.63 ± 0.35 mg/g), followed by a simple and low energy product recovery method through the addition of water and precipitation. COSMOtherm calculations suggested that the extraction efficiency was related to solvent interactions with the cell walls of the biomass, rather than the solubility of the curcuminoids. In addition, the application of ultrasound in extraction in combination with DES-B5 enabled the strong destruction of the plant matrix that was confirmed by scanning electron microscopy. The sustainability, efficiency, and toxicity of the proposed extraction methodologies were evaluated through the CHEM21 green metrics toolkit. The methods utilizing ethanol, ethyl acetate, and Cyrene in this work demonstrate a significant improvement over those previously published by 3-10 times of process mass intensity total, and DES-B5 also performed well under the green metrics assessment. Because of its high yields, low toxicity, being a bio-based solvent, inexpensive, and readily available, DES-B5 with 10% water is recommended as the greenest solvent for curcuminoid extraction under ultrasonication.
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Financial support from Center of Excellence for Innovation in Chemistry (PERCH-CIC) and Ministry of Higher Education, Science, Research and Innovation is gratefully acknowledged. This work was also supported by Materials Chemistry Research Center (MCRC) and Natural Products Research Unit, Khon Kaen University. Andrew Hunt would like to acknowledge the financial support of the Thailand Research Fund (grant number RSA6280031) and Khon Kaen University. We would like to thank Circa Group Pty Ltd. for the provision of Cyrene. COSMO-RS calculations are courtesy of, and authorized for the purposes of, Circa Group Pty Ltd.
- Curcuma longa
- deep eutectic solvents
- tetramethyloxolane (TMO)