Eugenol-Loaded Microemulsions: Characterization, Antibacterial Activity, and Fresh-Cut Lettuce Sanitization

Eugenol, a major bioactive compound present in various essential oils with substantial antibacterial activity, has limited application in food industries due to its low water solubility. To address this limitation, a microemulsion system was developed utilizing Tween 80 as a surfactant and lactic acid as a co-surfactant to facilitate the delivery of eugenol. The resulting microemulsion underwent physicochemical characterization, antibacterial evaluation, and sanitation trials on fresh-cut lettuce. Phase analysis revealed three distinct types of microemulsions with stability and dispersibility: water-in-oil with 0%–20% water, bicontinuous with 30%–60% water, and oil-in-water with 70%–90% water. Antibacterial assays indicated minimum inhibitory concentrations of 0.5 mg/mL for Staphylococcus aureus and 0.25 mg/mL for Escherichia coli , along with minimum bactericidal concentrations of 1 and 0.5 mg/mL, respectively. Furthermore, the microemulsion at 1 mg/mL exhibited rapid bactericidal effects against both bacterial strains, achieving a population reduction of over 6-log units within 10 min. In refrigerated fresh-cut lettuce sanitation experiments, microemulsion concentrations of 0.25, 0.5, and 1 mg/mL effectively suppressed the number of total microbes, mold, and yeast, with 0.5 mg/mL treatment being most effective in maintaining lettuce quality and freshness. Additionally, these treatments contributed to the preservation of vitamin C content, chlorophyll level, and color stability. Overall, the results demonstrate that eugenol microemulsions hold strong potential as green sanitizers for vegetables, offering a promising avenue to enhance food safety and quality.