Upcycling Citrus aurantium leaf by‑products into bioactive phenolics: Ionic liquid-ultrasound synergy for green extraction, UPLC-QTOF-MS/MS profiling, and hypoglycemic activity

Large quantities of agri-food by-products arise from citrus processing, creating disposal challenges but also opportunities for valorization. To address this, this study aimed to recover bioactive phenolics from C itrus aurantium leaves (CAL) and to define their composition and bioactivity. First, was screened 16 ionic liquids and identified 1-hexyl-3-methylimidazolium chloride ([C 6 mim]Cl) as the optimal-polarity solvent for phenolic extraction. Building on this, an ionic liquid–ultrasound synergistic extraction (IL–USE) process was developed and optimized using single-factor experiments combined with response surface methodology. Under the optimal conditions (0.35 mol/L [C 6 mim]Cl, liquid-to-solid ratio 27 mL/g, ultrasonic power 280 W, 50 min, 55 °C), the total phenolics yield reached 80.57 ± 0.60 mg/g. Compared with ultrasound-assisted extraction and conventional heat-reflux extraction, IL-USE delivered higher yields. This enhancement was macroscopically reflected in the scanning electron microscopy (SEM) analysis, which revealed more pronounced cell-wall disruption. For downstream enrichment, among five macroporous resins evaluated, HPD-826 performed best, and subsequent optimization of breakthrough and elution parameters afforded a CAL total phenolics (CAL-TP) fraction with 77.45 ± 1.63% purity. Furthermore, UPLC-QTOF-MS/MS tentatively identified 47 constituents, establishing a robust chemical profile of CAL-TP. Functionally, in insulin-resistant HepG2 cells, CAL-TP increased glucose consumption and glycogen synthesis and enhanced hexokinase and pyruvate kinase activities, thereby indicating hypoglycemic potential. Collectively, this study provides a green and efficient process that yields phenolic-rich fractions from CAL with defined composition and promising antidiabetic activity.