Sustainable extraction of polyphenols from millet using switchable deep eutectic solvents

In this study, polyphenols were extracted from millet with a high hydrostatic pressure (HHP) pretreatment combined with switchable deep eutectic solvent (DES) extraction. The antioxidant activity of the extract was evaluated, and the switchable DESs were recycled and reused. HHP pretreatment destroyed the cell structure of millet to facilitate the extraction of polyphenols. The grinding-assisted extraction was used as the extraction method by taking switchable DES (octanoic acid-linalool) as the extraction solvent and beta-cyclodextrin as the auxiliary extraction reagent. The hydrophilic DES was switched to the hydrophobic DES to recover millet polyphenols. The hydrophobic DES was recycled and switched to the hydrophilic DES for extracting new millet samples. After being reused five times, the yield of millet polyphenols using recycled DESs did not decrease significantly. In conclusion, HHP pretreatment combined with switchable DES extraction is considered as a green, efficient, and sustainable method for bioactive compounds.