Strategies for the purification of hydroxytyrosol-rich extracts obtained from exhausted olive pomace

Exhausted olive pomace (EOP) is a residual biomass from which hydroxytyrosol can be recovered. This compound has applications in the food/pharma sectors, but its extraction yields complex extracts that require further purification for some applications.This work explores purification strategies based on membrane technology, liquid-liquid extraction (LLE), and solid-phase extraction with adsorbents and resins. The hydroxytyrosol content, phenolic profile, antioxidant activity, and inhibition of alpha-glucosidase and alpha-amylase were monitored. Hydroxytyrosol stood out in all purified extracts. The best hydroxytyrosol recovery (88.8%) was achieved using LLE with ethyl acetate as the extractant, while the purest extracts in phenolic compounds, including hydroxytyrosol, were obtained using the latter solvent and C18 (529 mg/g), DSC-8 (873 mg/g), and Purosorb PAD910 (523 mg/g). Conversely, mannitol and glucose, at high concentrations in the extract, were selectively retained in the aqueous phases.The developed strategies are discussed regarding their suitability to provide hydroxytyrosol-concentrated extracts, up to 291 mg/g, with antioxidant and antidiabetic functionalities.