Ultrasound-assisted efficient extraction of polyphenols from Alpiniae oxyphyllae fructus using deep eutectic solvents: UHPLC-HRMS/MS characterization, antioxidant evaluation, and DFT calculations

This study presents a comprehensive characterization and comparison of polyphenols in Alpiniae oxyphyllae fructus extracted using ultrasound-assisted deep eutectic solvents (DESs) versus traditional solvents. The contents of total polyphenols in Choline chloride -malic acid (ChCl-MA) (1:1) , ChCl-MA (1:2) , L-proline-Lactic acid (Pro-LA) (1:1) , Pro-LA (1:3) , and L-proline-citric acid (Pro-CA) (1:3) extracts were the highest, ranging from 17.67 to 19.37 mg/g, and were significantly higher than those in water extract (10.35 mg/g) and ethanol extract (14.78 mg/g) ( p  < 0.05). Pro-LA extract exhibited high levels of 3,4-dihydroxybenzoic acid and protocatechualdehyde, and possessed strong antioxidant activity. Density functional theory (DFT) calculations indicated that the mechanism of DESs' efficient extraction of polyphenols was mainly reflected in the unique structural configuration of Pro-LA, which facilitated the formation of strong hydrogen bonds with the hydroxyl functional groups of polyphenols, enhancing the intermolecular interaction, and thus improving the extraction efficiency. Our study provided a novel approach for the efficient extraction of plant polyphenols.