Nanoemulsion enhances antimicrobial efficacy of Spanish marjoram essential oil against Listeria monocytogenes and E. coli O157:H7 on spinach leaves

Minimally processed vegetables due to the lack of thermal processing during manufacturing are at increasing risk of microbiological contamination. Effective disinfection strategies are therefore critical to ensure the safety of these products.

This study investigated the potential of Spanish marjoram essential oil (SMEO) nanoemulsion as a sustainable alternative to commercially used chlorine-based products for disinfecting minimally processed leafy greens. In the first stage of this study three SMEO nanoemulsion formulations were prepared using different concentrations of Tween 80 surfactant (0.5 % to 5 %) via ultrasonic homogenization. The nanoemulsions were characterized for particle size, polydispersity index, zeta potential, storage stability and antibacterial activity. Minimum Inhibitory Concentration (MIC) and the Minimum Bactericidal Concentration (MBC) were determined against Listeria monocytogenes and Escherichia coli O157:H7. Increasing Tween 80 concentration significantly improved nanoemulsion properties, reducing droplet size, enhancing homogeneity, and storage stability. The MIC and MBC values ranged from 0.78 to 1.56 mg/mL for all the formulations. Afterwords, selected SMEO nanoemulsion at 1xMICs and 2xMICs concentrations were compared to 0.02 % sodium hypochlorite (NaOCl) against L. monocytogenes and E. coli O157:H7 on spinach leaves. Both SMEO nanoemulsions exhibited significant antimicrobial activity, effectively reducing pathogen populations on produce surfaces with similar or better effectiveness compared to NaOCl. Furthermore, the application of the nanoemulsion did not adversely affect the color or visual quality of spinach leaves. This study supports the use of SMEO nanoemulsion as an effective and eco-friendly alternative to traditional chemical sanitizers for maintaining the safety and quality of fresh produce.