Green recovery of phenolics from bitter orange flowers: Natural deep eutectic solvent-ultrasound synergistic extraction, adsorptive purification, and UPLC/Q-TOF-MS/MS analysis

Bitter orange flowers (BOF), a renowned medicinal and edible botanical resource, are rich in phenolic compounds with significant potential for health and industrial applications. However, efficient extraction and purification techniques for recovering bioactive phenolics remain underexplored. To address this gap, this study aimed to develop an eco-friendly integrated strategy combining natural deep eutectic solvent-ultrasound synergistic extraction (NADES-USE) with adsorptive purification for efficient recovery of total phenolics from BOF (BOF-TP). First, choline chloride-ethylene glycol (ChCl-EG) was determined to be the optimal extraction solvent from 12 synthesized NADESs and 3 common solvents. Employing Box-Behnken design (BBD), the optimized parameters for NADES-USE (38 % aqueous ChCl-EG, 18 mL/g, 345 W, 43 min, and 55 °C) resulted in a BOF-TP yield of 104.58 ± 0.34 mg/g, which was 1.30 to 2.16 times higher than those achieved with conventional solvents. Then, AB-8 resin demonstrated optimal adsorption-desorption performance for BOF-TP, with adsorption behavior strongly conforming to Langmuir isotherm and pseudo-second-order kinetic models. Thermodynamic analysis confirmed a spontaneous, exothermic physisorption process with decreasing entropy. The breakthrough curves and gradient elution curves were utilized to establish a chromatographic purification process for crude BOF-TP extracts, achieving a purity of 75.62 ± 0.95 %. Finally, a validated UPLC-Q/TOF-MS/MS method facilitated comprehensive chemical characterization and simultaneous quantification of seven bioactive compounds, serving as a basis for the quality control of purified BOF-TP extracts. In conclusion, this work demonstrates that the combination of NADES-USE and adsorptive purification offers significant potential for producing highly purified BOF-TP extract for further use in food and pharmaceutical applications.