Ultrasound-assisted deep eutectic solvent extraction and macroporous resin enrichment of polyphenols from Cortex Mori: Screening of tyrosinase inhibitors via affinity ultrafiltration-LC-MS and molecular docking.

Cortex Mori, the dried root bark of Morus alba L., is a rich source of polyphenolic compounds. In this study, an ultrasound-assisted deep eutectic solvent (UAE-DES) strategy was developed for the efficient extraction of polyphenols from Cortex Mori, combined with macroporous resin enrichment and subsequent chemical and functional characterization. Among 36 deep eutectic solvents evaluated, betaine-sucrose (DES-6) exhibited the best extraction performance. Response surface methodology optimized the UAE-DES conditions as 35% water content, 57 °C, liquid-to-solid ratio of 90 mL/g, ultrasound time of 20 min, and power of 520 W, achieving a total phenolic yield of 232.93 ± 0.95 mg GAE/g, which was 28.31% and 32.78% higher than the highest yields obtained using methanol and ethanol, respectively. Scanning electron microscopy revealed that ultrasound-DES treatment caused pronounced erosion, pore formation, cracking, and partial collapse of plant cell walls, thereby facilitating solvent penetration and mass transfer. After purification using HPD-100 resin, UHPLC-Q-Orbitrap HRMS identified 58 polyphenolic compounds, including 11 reported from Cortex Mori for the first time. The 70-W2 fraction exhibited strong tyrosinase inhibitory activity (IC50 = 1.92 ± 0.03 µg/mL), surpassing kojic acid (IC50 = 12.54 ± 0.21 µg/mL). Affinity ultrafiltration coupled with LC-MS (UF-LC-MS) screening identified seven potential tyrosinase-binding ligands. Molecular docking showed that 2-hydroxynaringenin 4'-O-glucoside had the most favorable predicted docking score (-10.5 kcal/mol), followed by mulberroside A and 5,7,2',6'-tetrahydroxyflavanone. These candidates require further biochemical and in vivo validation. In addition, the optimized DES retained 90.51 ± 2.28% of its initial extraction performance after the third reuse cycle, while FTIR, viscosity, and density analyses supported its short-term physicochemical stability. These results demonstrate that ultrasound-assisted deep eutectic solvent extraction provides an integrated and resource-efficient approach for polyphenol recovery, activity-oriented enrichment, and prioritization of potential tyrosinase-binding constituents from Cortex Mori.