Olive Tree By-products as a Source of Bioactive Molecules

Abstract The olive sector generates millions of tons of annual residues including leaves, pomace, pits, olive mill wastewater, and table olive effluents that impose an environmental burden while harboring structurally diverse, high-value phenolic bioactives including hydroxytyrosol, oleuropein, tyrosol, ligstroside, oleacein, and oleocanthal. Despite growing interest in valorizing these matrices within a circular bioeconomy framework, a fragmented literature has obscured the most productive sources, dominant bioactive profiles, and scalable processing routes relevant to the food industry. This review comprehensively examines the phenolic composition, green extraction technologies, antimicrobial, antioxidant, and anti-inflammatory mechanisms, and food-system applications of the principal olive by-product streams. Key findings reveal that olive leaves deliver the highest oleuropein concentration (up to 160 g/kg DW), olive mill wastewater supplies the richest free hydroxytyrosol pools (50–300 mg/L), and olive pomace provides oleacein and oleocanthal at commercially relevant levels. Antimicrobial efficacy against priority foodborne pathogens including Listeria monocytogenes , Escherichia coli O157:H7, and Salmonella enterica operates through simultaneous membrane disruption, enzyme inhibition, reactive oxygen species generation, metal chelation, and quorum-sensing interference. Validated food-system applications include phenolic nanocomposite coatings, pH-responsive smart packaging films, and microencapsulated functional ingredients with preserved bioactivity over extended storage. Future research should prioritize standardized characterization protocols, AI-assisted biorefinery optimization, and robust in vivo bioavailability validation to bridge the gap between demonstrated bioactive potential and commercially viable, clean-label food preservation solutions.