Efficient extraction of flavonoids from Cercis chinensis bark using ultrasound-assisted deep eutectic solvents: Process optimization, characterization, kinetic studies, antioxidant and enzyme inhibition activities

This study presents an efficient and eco-friendly approach for extracting flavonoids from Cercis chinensis bark using ultrasound-assisted deep eutectic solvent (UAE-DES) extraction. Among 13 screened DES systems, L -proline-sorbitol (molar ratio 1:2, DES-9) exhibited the maximum extraction yield (51.2 mg/g), significantly outperforming conventional 60 % ethanol extraction. An optimal flavonoid yield of 87.6 mg/g was achieved through the optimization of key parameters (ultrasonic temperature, ultrasonic time and water content) using Response Surface Methodology, with the ideal conditions identified as 42 °C, 40 min and 8 % water. UPLC-Q-Exactive Orbitrap MS analysis revealed that C. chinensis bark flavonoids were mainly composed of quercetin, astragalin, kaempferol and afzelin. Scanning electron microscopy (SEM) showed that DES-9 induced severe cellular disruption, enhancing flavonoid release. Extraction kinetics followed a pseudo-first-order model, with a calculated apparent activation energy of 3.53 kJ/mol, indicating a diffusion-controlled process. The DES extract demonstrated superior antioxidant and enzyme inhibitory activities compared with the 60 % ethanol extract. Additionally, DES recovery via macroporous resin achieved an 87.23 % flavonoid recovery rate, with the solvent maintaining over 80 % efficiency after three reuse cycles. These findings underscore the UAE-DES method as a sustainable and effective strategy for valorizing C. chinensis bark into high-value natural medicinal products.