Purpose: In the present study, the inhibitory effect of six essential oils/derivatives (basil, thyme, nutmeg and oregano oil, trans-cinnamaldehyde, and eugenol), their binary mixtures, and emulsions was investigated on Salmonella Typhimurium ATCC 19585 in a broth model system.
Methods: Minimum Inhibitory Concentration (MIC) and diameters of Zone of Inhibition (ZOI) of oils/derivatives dissolved in ethanol against S. Typhimurium were determined utilizing Broth Dilution Method and Disc Diffusion Method, respectively. Synergistic effect was monitored by Checkerboard assay method and then Fractional Inhibitory Concentration (FIC) was calculated. Oil-in-water emulsions were prepared by sonication utilizing Tween 80 as an emulsifier. MICs were then evaluated on S. Typhimurium.
Results: Trans-cinnamaldehyde and oregano oil were most effective in S. Typhimurium inhibition (ZOI: 22, 21 mm; MIC: 312.5 ppm), followed by eugenol and thyme oil (ZOI: 19, 14 mm; MIC: 625 ppm), and nutmeg oil and basil oil (ZOI: 14, 15 mm; MIC: 1250 ppm). All binary combinations of oils exhibited synergistic effect as indicated by the FIC ≤ 0.5, though MIC values were higher for emulsions (nutmeg and basil oil: >5000 ppm; eugenol: 5000 ppm; thyme oil: 2500 ppm; oregano oil, trans-cinnamaldehyde: 625 ppm) than those for the oils dissolved in ethanol.
Significance: Combinations of essential oils/derivatives have potential to be used as food additives for increased safety.