Ultrasound-assisted extraction of flavonoids from Cercis chinensis flowers using deep eutectic solvents: optimization, characterization, kinetics and bioactivity

This study demonstrates an efficient and eco-friendly method for extracting flavonoids from Cercis chinensis flowers using ultrasound-assisted deep eutectic solvent (UAE-DES) extraction. Among 17 DES systems screened, L-Proline-Lactic acid (DES-11) achieved the best extraction yield (56.53 mg/g), significantly surpassing that of conventional 60 % ethanol extraction (13.65 mg/g). Through Response Surface Methodology optimization of key parameters (ultrasonic temperature, time, and water content), a maximum flavonoid yield of 95.84 mg/g was obtained under ideal conditions: 32 % water, 36 °C, and 31 min. Scanning electron microscopy (SEM) analysis revealed that DES-11 caused substantial cellular disruption, facilitating flavonoid release. Extraction kinetics followed a pseudo-first-order model, with a calculated apparent activation energy of 20.48 kJ/mol, consistent with a diffusion-controlled mechanism. Additionally, 34 flavonoids were identified for the first time in the DES extract using UPLC-timsTOF-MS. The DES extract exhibited superior antioxidant activity in radical scavenging assays compared to the ethanol extract. Furthermore, DES recovery via macroporous resin yielded an 86.64 % flavonoid recovery rate, and the solvent retained over 84.93 % efficiency after four reuse cycles. These results highlight the UAE-DES method as a sustainable and effective strategy for transforming C. chinensis flowers into high-value natural antioxidants.