Recovery of Hydroxytyrosol from Olive Pomace: Extraction, Purification, Bioactivity, and Bioavailability.

Olive pomace (OP), the main by-product of olive oil production, is a rich source of phenolic compounds, among which hydroxytyrosol (HT) has received considerable attention because of its biological activity. This review examines the occurrence of HT in OP and the factors that influence its formation during processing, with particular attention to the intrinsic compositional variability arising from cultivar differences, irrigation regimes, fruit maturity, and extraction systems, which collectively challenge industrial reproducibility. Current strategies for HT extraction and purification are reviewed, and the technological readiness of each method is evaluated. The biological activities of HT, particularly its antioxidant, anti-inflammatory, and cardioprotective effects, are summarized alongside a critical assessment of in vivo bioavailability data. Key research gaps are identified throughout: no pilot-scale integrated purification train has been validated, life cycle assessments comparing different recovery routes are absent, and most delivery systems lack in vivo pharmacokinetic evaluation. By bringing together studies on HT recovery and its functional properties, this review highlights the promising yet underdeveloped potential of OP as a sustainable feedstock for HT recovery and identifies the critical steps needed to advance from laboratory research to industrial application.