Comprehensive and consumption-saving process optimization of extracting five polyphenols from Terminalia chebula Retz. by ultrasonic-assisted extraction combined with natural deep eutectic solvents

Achieving green, low-energy and efficient extraction is tough. In this study, ultrasonic-assisted extraction combined with natural deep eutectic solvents (UAE-NADESs) was used to extract gallic acid, corilagin, chebulagic acid, chebulinic acid and ellagic acid from Terminalia chebula Retz. (TCR). 1,3-butanediol-lactic acid (1,3BD-LA) was identified as the optimal NADES through various statistical analyses [column chart + correlation analysis + principal component analysis (PCA)]. A comprehensive, novel and consumption-saving combination optimization method, which was Plackett-Burman (PB) + steepest ascent test (SAT) + definitive screening design (DSD) + genetic algorithm (GA), was adopted to determine the optimum extraction process conditions. The conditions were as follows: molar ratio 1:3, water content 25 %, liquid to material ratio 45:1 mL/g, extraction time 44 min, extraction temperature 61 degrees C, and vortex time 15 s. The total extraction yield of five polyphenols was 201.31 +/- 0.80 mg/g, which was 1.07 times that of best conventional solvent (60 % ethanol). The extraction yields of gallic acid, chebulagic acid, chebulinic acid were 1.09, 1.11 and 1.11 times that of 60 % ethanol, respectively. Besides, the NADES extract had good antioxidant activities. Compared with various literatures, it's found that the established extraction and analysis methods were practical, simple and energy-saving. In addition, the properties of the optimal NADES and its potential mechanism of improving the extraction yield of gallic acid were proved by Fourier transform infrared spectroscopy (FT-IR) and COSMO model, respectively. Therefore, this study has found a suitable scheme for the efficient extraction and process optimization of polyphenols in TCR. Meanwhile, it provided a reference for the application of NADESs in the extraction of polyphenols or other similar components, and also provided a new idea for the application of combinatorial optimization method in the extraction experiment of effective compounds. It will add new ideas for the application of TCR extract as an antioxidant in food and medicine industries.