Sustainable Recovery of Phenolic Compounds from Orange Peel Using NADES–Resin Integrated Systems: Optimization and Mechanistic Insights

Abstract Citrus byproducts, particularly orange peel, represent a valuable source of phenolic compounds with recognized antioxidant and health-promoting properties. However, conventional extraction methods often rely on organic solvents, raising environmental and safety concerns. To address these limitations, this study proposes a green and sustainable approach for phenolic recovery using natural deep eutectic solvents (NADES) combined with macroporous resins. Four NADES formulations and three resin types (HP2MG, HP20, XAD-7) were evaluated. Process optimization was performed only for the resin-based recovery/purification step using response surface methodology (RSM) with a Central composite design, evaluating the extract-to-resin ratio, contact time, washing water volume, and resin type. Total phenolic content (TPC) was quantified by the Folin–Ciocalteu method, and phenolic profiles were characterized by LC–MS. Optimal conditions included 1 g of resin per 6 mL of extract, 40 min stirring, 15 mL washing water, and XAD-7 resin. Under these conditions, TPC recovery exceeded 70% for all NADES, reaching 94.59% for LA:Glu. NADES recycling was feasible, with residual phenolics below 3%. Chromatographic analysis revealed that ChChl:LP:MA combined with XAD-7 achieved the highest recovery for key compounds such as ferulic acid (217.07 µg/mL), narirutin (43.77 µg/mL), and hesperidin (60.00 µg/mL). Differences in recovery efficiency were attributed to the polarity and viscosity of NADES and the physicochemical properties of the resins. These findings demonstrate that NADES–resin systems are an effective and environmentally friendly alternative to conventional extraction methods, enabling the valorization of citrus byproducts and supporting circular economy strategies.