Ultrasonic-assisted customized natural deep eutectic solvents extraction of polyphenols from Chaenomeles speciosa

In this study, ultrasonic-assisted natural deep eutectic solvents method (UAE-NADESs) was applied to greenly and efficiently extract five polyphenols (chlorogenic acid, (+)-catechin, protocatechuic acid, caffeic acid and gallic acid) from Chaenomeles speciosa (CSP), and their contents were simultaneously determined by HPLC. On the basis of 9 kinds of customized NADESs, the best compositions were selected. Choline chloride-urea-malonic acid (ChCl-Ur-MA) was screened as the optimal compositions of NADES. The effects of six single factors on polyphenols contents were investigated. Afterwards, the combination of response surface methodology (RSM) and genetic algorithm (GA) was adopted to optimize process parameters, and results of optimal parameters were as follows: molar ratio of 1:3:3, water content of 31%, liquid–solid ratio of 11: 1 mL/g, vortex time of 30 s, extraction time of 40 min and extraction temperature of 60°C. The total yield of five components was 3.92 ± 0.03 mg/g, which was higher than traditional organic solvents. Among them, the extraction yield of (+)-catechin was improved significantly. Meanwhile, the hydrogen bond of ChCl-Ur-MA was verified by Fourier Transform Infrared Spectroscopy (FT-IR). The Sigma profiles (σ-profiles) of (+)-catechin, different NADESs, methanol and water were calculated and analyzed by COSMO model. The mechanism of discrepancie in extraction yield of (+)-catechin between NADESs and traditional organic solvents were discussed. In addition, the antioxidant activities of the extracts were determined. Compared with 50% methanol extract, the optimal NADES extract has better DPPH, hydroxyl and ABTS radicals scavenging abilities. In a word, the ternary NADES used in this study is a new and green extraction solvent that can replace organic solvents to extract five polyphenols. This study provides a basis for the subsequent development of this NADES, and is helpful for the efficient extraction of the same types of polyphenols from other plants.