Changes in the Quality Parameters and Antimicrobial Activity of Ozonated Virgin and Pomace Olive Oils Under Different Storage Conditions

Ozonated olive oils have emerged as a promising alternative for natural antimicrobial agents in the food industry due to their potential to inhibit microbial growth. However, the stability and effectiveness of these oils under different storage conditions has not been thoroughly explored. This study examines the changes in the physicochemical properties and antimicrobial activity of ozonated virgin olive oil (VOO) and pomace olive oil (POO), stored at 4 °C and 20 °C for 6 months. The peroxide index (PI), acidity index (AI), iodine value (IV), and viscosity (V) were analyzed, along with their antimicrobial activity against <i>Escherichia coli</i> (STCC 45), <i>Pseudomonas aeruginosa</i> (STCC109), and <i>Staphylococcus aureus</i> (STCC 239). The results showed that both oils underwent changes in their physicochemical properties and antimicrobial activity over time. The PI initially increased up to day 30, with VOO reaching a peak value of 741.44 ± 32.16 meq O₂/kg and POO reaching 1067.23 ± 56.56 meq O₂/kg, but after this point, it began to decrease in both oils and at both temperatures (4 °C and 20 °C). The acidity index (AI) increased over time, particularly in POO, which reached a final value of 6.32 ± 0.14 mg KOH/g. Both oils showed a reduction in iodine value (IV), and an increase in viscosity (V) over time. In terms of antimicrobial activity, <i>P. aeruginosa</i> remained stable with an average inhibition zone of 9.41 ± 0.23 mm, while <i>E. coli</i> showed the greatest increase in activity over time, reaching 21.31 ± 4.01 mm in POO at 20 °C. On the other hand, <i>S. aureus</i> exhibited the highest average antimicrobial activity, with a mean inhibition diameter of 14.49 ± 0.36 mm, and the largest inhibition zone of Ø = 18.97 ± 1.46 mm observed after 180 days of storage. A Spearman correlation analysis revealed a strong positive relationship (ρ > 0.85, <i>p</i> < 0.05) among PI, AI, and the antimicrobial activity with storage duration. This study provides novel insights into the stability of ozonated oils, offering valuable perspectives for their application in the food industry, especially using pomace olive oil, a key by-product in olive oil production.