Extraction of polyphenols from Apocynum venetum leaves using customized deep eutectic solvents: Process optimization and antioxidant evaluation

To encourage the commercial utilization of A. venetum polyphenols as bio-colorant on textile, five different combinations of deep eutectic solvents (DESs) were evaluated using a single-factor approach and the extraction of polyphenols from A. venetum leaves by ultrasound-assisted DESs was optimized. At the same time, the antioxidant activity of polyphenols prepared were investigated. The DESs composed of choline chloride and glycerol with a molar ratio of 1:2 and a water content of 20 % showed higher extraction performance than other DESs and traditional solvents (water, 60 % ethanol and 60 % methanol). With the most effective solvent the maximum yield 8.24 % of polyphenols was obtained under the optimal extraction conditions were as follows: the ratio of liquid volume (mL) to solid mass (g) is 49:1, extraction temperature of 77 ℃, and extraction time of 55 min. In addition, the polyphenols that have been separated and purified from the DESs extract exhibited antioxidant activities in three kinds of assays including 2,2-diphenyl-1-picrylhydrazyl stable free radical (DPPH), 2,2’-azino-bis-(3-ethylbenzothiazoline-6-sulfonic) acid free radicals (ABTS) and hydroxyl radical (•OH) scavenging activity. Therefore, this paper demonstrates that DESs are effective and environmentally friendly solvents extraction of antioxidant polyphenols pigments from the leaves of A. venetum.