Enhancing polyphenol recovery from NaDES extracts of olive oil by-products through polymeric resin purification

Olive oil production generates large amounts of leaf waste rich in phenolic compounds. This study aimed to purify olive leaf extracts obtained with a choline chloride-glycerol green solvent using polymeric resins, while removing co-extracted sugars and solvent residues. Two non-functionalized polymeric resins were evaluated through adsorption, aqueous washing, and ethanol-water desorption. Phenolic compounds were monitored by high-performance liquid chromatography, and antioxidant capacity was assessed using the Ferric Reducing Antioxidant Power assay. Two sequential water washes removed solvent residues with minimal phenolic losses. Resin selectivity differed by compound polarity and size: one resin favored recovery of small polar compounds, whereas the other improved recovery of larger flavonoids. An ethanol-water mixture of 70:30 enabled effective elution of key olive leaf phenolics. The optimized workflow produced antioxidant-rich purified fractions and provides a reproducible laboratory-scale strategy for improving the quality of green-solvent extracts intended for further food and cosmetic applications.