Integrated enzymatic biotransformation and food-grade deep eutectic solvent extraction of oxyresveratrol from mulberry branches for antibrowning applications

Mulberry branches, agricultural by-products generated during annual pruning, are rich in stilbenoids, which possess various promising bioactivities. In this study, a green strategy integrating enzymatic hydrolysis and food-grade deep eutectic solvents (DES) extraction was developed for the efficient extraction of oxyresveratrol (ORV) from mulberry branches. A multi-enzyme system combining cellulase, pectinase, and β-glucosidase enhanced ORV recovery, increasing the ORV yield by 49% under ethanol extraction, while scanning electron microscopy (SEM) revealed substantial disruption of the mulberry branch microstructure after enzymatic treatment. A DES (DES-9) composed of L-proline and malic acid (1:2 mol/mol) was optimized as the final solvent. Using a Box-Behnken design, the optimized DES extraction conditions were an extraction time of 30 min, a solid/liquid ratio of 1:21 (g/mL) and a water content of 19%, resulting in an ORV yield of 0.88 mg/g dry weight (DW). FTIR analysis suggested hydrogen-bonding interactions between DES-9 and ORV. In addition to serving as a green extraction medium, the food-grade DES enabled the utilization of this extract in food systems without extensive solvent removal. DES-extracted ORV (DES-ORV) was found to delay color deterioration in both apple juice and fresh-cut apple slices, while its combination with ascorbic acid (VC) exhibited enhanced antibrowning effects. These findings establish an integrated route from enzymatic biotransformation and green extraction to potential food application, providing a promising strategy for the value-added utilization of mulberry branches.