Green Tailoring With Water of Choline Chloride Deep Eutectic Solvents for the Extraction of Polyphenols From Palm Samples.

To address the problem of high viscosity of deep eutectic solvents (DESs), the viscosities of a series of choline chloride-based DESs and DESs-H2O were determined, and their extraction efficiencies were obtained for the extraction of polyphenols in palm samples. Tailoring the DESs by the addition of water successfully adjusted their viscosity from thousand to single-digit mPa s and aided the extraction of polyphenols from samples, by changing the hydrogen-bonding interactions of DESs. Among the compounds investigated, choline chloride-oxalic acid-water of DESs-H2O with various molar ratios with 1:0.1-1:50 showed the greatest change in viscosity with 3617-2 mPa s, and effectively extracted most of the target compounds of polyphenols (52.1 μg mL-1 for protocatechuic acid, 7.3 μg mL-1 for catechins, 34.0 μg mL-1 for epicatechin and 6.2 μg mL-1 for caffeic acid) from samples. The results confirm that tailoring with water can successfully adjust the viscosity and extraction efficiency of DESs, for effective extraction of bioactive compounds from samples.