An integrated green strategy based on deep eutectic solvents and ultrasound for efficient polyphenol profiling and antioxidant evaluation of dendrobium officinale

Deep eutectic solvents (DESs) combined with ultrasound-assisted extraction (UAE) have emerged as a promising green strategy for efficient recovery of bioactive compounds. In this study, a DES-based UAE system was developed for the extraction of polyphenols from Dendrobium officinale (DO), with particular emphasis on the synergistic effects and underlying mechanisms. Among 24 screened DESs, choline chloride-fructose (ChCl-Fru, 1:2) exhibited the highest extraction efficiency. Key extraction parameters were optimized using Plackett-Burman design and Box-Behnken design, yielding an optimal total polyphenol content (TPC) of 87.75 mg GAE/g DO. Kinetic modeling revealed that the extraction process followed a second-order model, indicating that both mass transfer and solute-solvent interactions governed the extraction behavior. Compared with silent conditions, ultrasound significantly enhanced extraction efficiency. The TPC obtained by DES-UAE (88.11 mg GAE/g DO) increased by 130% relative to silent DES extraction, which was notably higher than that observed in the 70% methanol system (107%). In addition, DES-UAE extracts exhibited superior antioxidant activities, with DPPH and ABTS scavenging rates of 90.79% and 96.46%, respectively. Molecular dynamics simulations further demonstrated that the DES system provided a more favorable solvation environment for phenolic compounds, characterized by enhanced hydrogen-bonding interactions, reduced molecular aggregation, and stronger binding energies compared with methanol. These findings reveal that the superior performance of DES-UAE originates from the synergistic interplay between ultrasonic cavitation and the unique physicochemical properties of DES. Chemical profiling by UHPLC-Q Exactive Orbitrap HRMS identified 31 phenolic compounds, including flavonoids, phenolic acids, biphenyls, and other derivatives. Multivariate statistical analysis revealed significant metabolic differences among DO samples from different geographical origins, and 11 key differential metabolites were identified as potential biomarkers. In addition, the DES-UAE extracts exhibited superior antioxidant activity compared to conventional ethanol extracts. Overall, this study provides a mechanistic understanding of DES-UAE systems and offers a green and efficient strategy for the extraction and utilization of polyphenols from DO.