Deep eutectic solvents-synergistic ultrasonic-assisted extraction of polyphenols from raspberry (Rubus idaeus L.): Optimization, mechanisms, and in vitro and cellular antioxidant activity.

This study explores an innovative approach based on deep eutectic solvents (DESs)-synergistic ultrasonic-assisted extraction (UAE) of polyphenols from raspberry (RB). Choline chloride-fructose (ChCl-Fru, 2: 1) was screened and exhibited the highest amounts of active compounds. The optimal conditions for ChCl-Fru-synergistic UAE (ChCl-Fru-UAE) were obtained as follows: ultrasonic power of 360 W, liquid-to-solid ratio of 10:1, and water content in ChCl-Fru of 50 %. Eight compounds were identified in the RB extracts by HPLC-MS/MS method. SEM results revealed that UAE disrupted the surface structure of the samples, thereby facilitating the release of phenolic compounds. Molecular dynamics simulations results confirmed that ChCl-Fru significantly enhanced solute-solvent interactions, especially for delphinidin-3-O-glucoside and ellagic acid, and thus showed higher extraction efficiency. In vitro chemical and cell assays verified that ChCl-Fru-UAE demonstrated stronger antioxidant activities. Overall, ultrasonic-synergistic DESs extraction could be an eco-friendly method for recovering high-value compounds from fruits and their byproducts.