Towards a sustainable recovery of polyphenols from agrifood waste: Performance of polymeric sorbents with natural deep eutectic solvent extracts

Olive oil production generates large amounts of waste, which contains phenolic compounds at relevant concentrations. In recent years, interest in the recovery of these compounds has grown to take advantage of their natural antioxidant properties. Natural deep eutectic solvents (NaDESs), considered as green solvents, have proved their efficiency to extract phenolic compounds from agri-food waste. The resulting extracts must be purified before being used in pharmaceutical, food, or cosmetic applications. In this study, the performance of several non-functionalized polymeric sorbents (PuroSorb PAD900, PAD950 and PAD610, and Macronet MN202) was evaluated for the purification of NaDES extracts (choline chloride-glycerol (1:5); 30% water) from olive tree leaves. It is important to highlight that these types of characterization studies are common for conventional solvent extracts but are very novel and scarce for their NaDES counterparts. Sorption was investigated at the natural conditions of the extracts (pH 5.3), and ethanol-water mixtures were used in the desorption experiments. Overall, the four sorbents displayed good sorption characteristics, with MN202 being particularly suited to retain 3-hydroxytyrosol. Ethanol levels above 70% were appropriate for desorption of most phenolic compounds, while mixtures with ethanol content below 50% were more efficient for small polar molecules such as 3-hydroxytyrosol.