Synergistic inhibition of bacteria associated with minimally processed vegetables in mixed culture by carvacrol and 1,8-cineole

This study assessed the effect of the combined application of carvacrol (CAR) and 1,8-cineole (CIN) against bacteria associated with minimally processed vegetables (MPV), namely Listeria monocytogenes, Aeromonas hydrophila and Pseudomonas fluorescens, in mixed culture. For this, Fractional Inhibitory Concentration (FIC) index, time-kill in vegetable-based broth, vegetable matrices and confocal and scanning electron microscopy analysis were carried out. CAR and CIN displayed Minimum Inhibitory Concentrations (MIC) of 1.25 and 40 μL/mL, respectively. FIC index of the combined compounds was 0.25 against the mixed inoculum, suggesting a synergic interaction. The application of CAR and CIN alone (MIC) or combined (1/8 MIC + 1/8 MIC) in vegetable-based broth caused a decrease (p < 0.05) in viable cell counts over 24 h. CAR and CIN in combination reduced (p < 0.05) the mixed inoculum in vegetable broth and in experimentally inoculated fresh vegetables. The exposure to these compounds changed the membrane permeability and caused ultrastructural changes in surfaces of bacterial cells. The enhancing inhibitory effects observed for subinhibitory concentrations of CAR and CIN in combination against a mixed culture of bacteria associated with MPV suggest that the combination of these compounds is effective for controlling bacterial growth and survival in these foods.