Comparison of antibacterial effects of essential oils against lactic acid bacteria in a laboratory medium and organic fruit juices

This study evaluated the antimicrobial efficacy of essential oils (EOs) and their combinations against lactic acid bacteria (LAB) responsible for spoilage in organic fruit juices under various matrix conditions. Among the 24 EOs tested, 4 EOs (cinnamon bark, cinnamon leaf, oregano, and thyme thymol) showed the strongest inhibitory effects against the 3 LAB strains. Their inhibitory and synergistic effects were evaluated in laboratory medium, Hallabong juice, and tomato juice matrices. Oregano and thyme thymol exhibited enhanced antimicrobial activity in acidic juices, with minimum inhibitory concentration decreasing to 0.078 μL/mL compared to 0.625 μL/mL and 1.25 μL/mL in deMan-Rogosa Sharpe broth, respectively. Checkerboard assays revealed that synergistic and partial synergistic effects of EO combinations varied depending on both the LAB strain and the juice matrix. Notably, synergy was more frequently observed in acidic matrices, particularly in Hallabong juice, likely due to the presence of organic acids such as citric and malic acids. The observed effects suggest that juice pH and matrix composition can significantly influence the efficacy of EO-based antimicrobial strategies. These findings support the potential application of tailored EO combinations as natural preservatives in minimally processed fruit juice products.