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

Olive leaves and olive oil residues are abundant by-products that can serve as alternative sources of antimicrobials. This study characterized extracts from Ascolano and Grappolo olive leaves and olive oil residues, focusing on phenolic content and antimicrobial activity. Aqueous and ethanolic extracts were tested against Listeria monocytogenes , Staphylococcus aureus , Bacillus cereus , Escherichia coli , and Salmonella Enteritidis , with HPLC (UV-vis) used for chemical analysis. Ethanolic extracts exhibited greater inhibition and higher phenolic compound concentrations. The Grappolo leaves ethanolic extract had a minimum bactericidal concentration of 50% for B. cereus , E. coli , and S. aureus and contained 9.24 ± 0.58 g.ml⁻¹ hydroxytyrosol. Olive oil residue ethanolic extracts showed high oleuropein content (16.47 ± 0.76 g.ml⁻¹) and inhibited B. cereus by 75%. The results highlight the potential use of olive leaves and residues of olive oil production extracts as natural and sustainable antimicrobials against some microorganisms that cause foodborne illness.