Valorization of Olive Pomace as a Source of Phenolic Compounds: Extraction Technologies, Analytical Characterization, Biological Activities, and Food Applications

The valorization of agro-industrial by-products has gained increasing attention as a sustainable strategy to support circular economy principles and reduce environmental impacts. Spain, the world’s largest olive oil producer, generates substantial amounts of olive pomace (OP), which can represent up to 80% of the processed olive mass. Due to their hydrophilic nature, approximately 98% of olive phenolic compounds remain in OP after oil extraction, making this by-product a valuable source of bioactive compounds with antioxidant, anti-inflammatory, antimicrobial, and cardioprotective properties. Numerous extraction strategies have been investigated to maximize phenolic recovery while reducing processing costs and environmental impacts. Conventional solvent-based techniques, such as solid–liquid extraction (SLE) and liquid–liquid extraction (LLE), remain widely used, while greener approaches, including microwave-, ultrasound-, supercritical fluid-, pressurized liquid-, and high-pressure-assisted extraction, among others, have gained increasing attention. In addition, deep eutectic solvents (DES) have been applied either alone or in combination with green extraction technologies to enhance extraction efficiency. This review provides a comprehensive overview of extraction techniques for OP valorization and the analytical methodologies used to characterize OP extracts, including spectrophotometric and chromatographic approaches. The biological activities of OP-derived phenolics and their food applications are also discussed, highlighting their valorization potential.