Abstract:In order to explore an efficient，green，and sustainable method for extracting polyphenols from Forsythia suspensa red tea，ultrasonic-assisted switchable deep eutectic solvent （DES） was used to extract polyphenols using Forsythia suspensa red tea as raw material. Based on single-factor experiments，response surface methodology was designed to optimize the extraction process. By utilizing the characteristics of switchable DES，the hydrophilic DES used for extraction was switched to a hydrophobic state to realize the recovery of hydrophobic DES，and the recovered hydrophobic DES could be switched back to hydrophilicity for the continuous extraction of Forsythia suspensa red tea polyphenols. The results showed that the extraction yield of Forsythia suspensa red tea polyphenols by switchable DES was higher than that by water or 60% ethanol solution，which was 2.65 times and 1.31 times，respectively. The optimal extraction conditions were obtained as follows：solid-liquid ratio of 1∶40 （g/mL），ultrasonic temperature of 70 ℃，and ultrasonic time of 43 min. Under these conditions，the yield of Forsythia suspensa red tea polyphenols was （82.590 3±0.377 7） mg/g. The yield of polyphenols remained high after the switchable DES was reused for four times.