Unveiling the synergistic antioxidant and antimicrobial effects of polyphenolic compounds from olive by-products

The olive oil industry annually generates a substantial quantity of liquid and solid olive by-products, including leaves from harvesting and pruning. These residues represent a valuable, underutilized source of bioactive molecules. This study focused on the extraction and chemical characterization of phenolic fractions from these by-products. Chemical analysis of the extracts identified 16 distinct phenolic compounds, primarily from the families of hydroxybenzoic acids, hydroxycinnamic acids, secoiridoids, and flavonoids. To evaluate the functional potential of these extracts, their antioxidant and antimicrobial activities were assessed. Antioxidant capacity of phenolic extracts was comprehensively determined using four complementary assays: total antioxidant capacity (TAC), ferric reducing antioxidant power (FRAP), DPPH radical scavenging, and the ABTS radical cation decolorization. These methods enabled a comprehensive assessment of the extracts' capacity to neutralize free radicals and reduce oxidizing species. Furthermore, the antimicrobial potential of the extracts was evaluated against various pathogenic strains. Antibacterial efficacy was tested on both Gram-negative ( Escherichia coli K12, Pseudomonas aeruginosa CIP 82.114, and Klebsiella pneumoniae CIP A22) and Gram-positive bacteria ( Bacillus subtilis ATCC 6633 and Staphylococcus aureus ATCC 29213). Antifungal activity was assessed against Candida albicans ATCC 10231, Aspergillus flavus MTCC 9606, Aspergillus niger MTCC 282, and Fusarium oxysporum MTCC 9913. The results underscore the potential of olive by-products as a source of high-value functional ingredients. This study investigated the synergistic effect of combining extracts from three by-products: olive mill wastewater, pomace, and leaves, to determine if their combination could enhance the previously reported biological properties. The results confirm the high potential of phenolic extracts from olive by-products as a valuable source of bioactive compounds, thus paving the way for their use in developing natural antioxidant and antimicrobial formulations and offering promising applications in food, pharmaceutical, and cosmetic industries.