Switchable deep eutectic solvents for sustainable extraction of β-carotene from millet

Switchable deep eutectic solvents (DESs) were combined with phenolic antioxidants to extract β-carotene from millet, and the recovery and reuse capacities of DESs were evaluated. The pre-treatment of millet using ultrafine grinding is beneficial to the extraction of β-carotene. The hydrophobic DESs synthesized from N,N-dimethylcyclohexylamine and n-butanol were used as the extractants for grinding-assisted extraction of β-carotene from millet, and phenolic antioxidants were used to improve the stability of β-carotene. The hydrophobic DESs were switched to hydrophilic DESs by adjusting pH to recover the hydrophobic β-carotene solid. The remaining hydrophilic DESs could be switched to hydrophobic DESs by adjusting pH to extract new millet samples. In five DES recovery and reuse processes, the yield did not decrease, and more than 91.0% of β-carotene from millet could be directly recovered in solid state each time. In summary, a rapid, efficient, and sustainable method for β-carotene extraction was developed.