Optimization of Deep Eutectic Solvent-Ultrasonic Assisted Extraction and Component Analysis of Polyphenols from Chestnut Shells

In this study, deep eutectic solvents (DESs) coupled with ultrasound-assisted extraction (UAE) were applied to extract polyphenol from chestnut shells and the components were identified. Eight different DESs were evaluated as candidate solvents and fourier transform infrared spectroscopy (FTIR) was performed to confirm the formation of hydrogen bonds between hydrogen bond acceptor and hydrogen bond donor. Based on the single factor experiments, the response surface methodology (RSM) was applied, ultrasonic power, liquid-solid ratio and water content were further evaluated in order to optimize the total ployphenol yield. Besides, the extracts were recovered by macroporous resin for the identification of phenolic compounds. As a result, DES-1 (choline chloride:oxalic acid=1:1) exhibited a highest extraction yield. After that, DES-1-based UAE process was optimized and the optimal conditions were as follows: Ultrasonic power 348 W, liquid-solid ratio 42:1 mL/g and water content 32%. The extraction yield (99.66±2.63) mg/g of the model validation experiment was demonstrated to be in accordance with the predicted value 99.44 mg/g, which was significantly higher than that obtained by using traditional solvents (water and 40% ethanol). In addition, phenolic compounds was efficiently recovered from DES extracts with high recovery yield (97.92%±1.78%) by using AB-8 macroporous resin. 13 phenolic compounds were preliminarily identified from DES-1-based UAE extracts by UHPLC-Q-TOF-MS/MS. In conclusion, this study would provide a green and efficient method to extract polyphenols from chestnut shells, providing technical support for the development and utilization of chestnut shells waste.