Sustainable extracts from oliviculture by-products: Phenolic content and its antimicrobial activity against foodborne pathogens

Abstract

Olive leaves and two-phase olive pomace (alperujo) are abundant agro-industrial by-products with potential as sustainable sources of bioactive compounds. In this study, aqueous and 70% ethanolic extracts obtained from leaves of the Ascolano and Grappolo cultivars and from alperujo were characterized for their phenolic composition and evaluated for antimicrobial activity against foodborne pathogens, including Listeria monocytogenes, Staphylococcus aureus, Bacillus cereus, Escherichia coli, and Salmonella Enteritidis. Phenolic compounds were analyzed by HPLC-UV/Vis, and antimicrobial activity was assessed by broth microdilution and minimum bactericidal concentration assays. In general, ethanolic extracts showed broader phenolic profiles and stronger antimicrobial effects than aqueous extracts, indicating more efficient recovery of active compounds by hydroalcoholic extraction. The ethanolic extract of Grappolo leaves showed the highest antibacterial activity, achieving > 90% inhibition against B. cereus, E. coli, and S. aureus, and was the only extract to exhibit bactericidal activity at 50% against these microorganisms. This extract was also characterized by high hydroxytyrosol content, whereas the ethanolic alperujo extract showed the highest oleuropein concentration. The stronger activity of ethanolic extracts is likely related to their greater ability to solubilize phenolic compounds with antimicrobial relevance, particularly hydroxytyrosol and oleuropein, which may act through membrane disruption, interference with permeability, and impairment of essential cellular functions. Overall, the results support olive leaves and alperujo as promising low-value raw materials for recovering phenolic-rich extracts with potential applications as natural antimicrobial agents in food systems. To improve reproducibility and practical applicability, standardization of extract yield and concentration should be considered in future studies.

Keywords

antimicrobial activity / food additives / olive leaves / residue / sustainability

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