Resumo

Besides minimizing microbial contamination of food, the active compounds found in essential oils are considered natural substances which attend consumers demand. The central composite rotational design with three center points 2² (total of 11 trials) was used for the evaluation of the sensitivity of Listeria monocytogenes strains to eugenol, limonene and their combinations. The variables studied were the concentration of eugenol (0 to 0.0125%) and the concentration of limonene (0 to 0.05%), with the maximum level being determined by the minimum inhibitory concentration. The active compounds eugenol, and limonene were combined and added to a tube containing 10mL of Muller-Hinton broth in order to obtain the compounds diluted in culture media at the concentration determined by the experimental design. Then, 100μL of each L. monocytogenes isolate was individually inoculated to a final concentration of 10⁶ CFU.mL^-1 and incubated at 37^oC for 24h. After the incubation, the tubes were serial diluted in 0.1% peptone solution and an aliquot of 100μL was spiked in duplicate on the surface of trypticase soy agar containing yeast extract. The plates were incubated at 37^oC for 24 to 48h and the result was expressed as CFU.mL^-1. The strains of L. monocytogenes Scott A and L. monocytogenes ATCC 35152 were, in general, more sensitive to eugenol, limonene and their combinations when compared to the food isolates (L. monocytogenes 1/2c, L. monocytogenes 1/2a e L. monocytoges f) and the clinical isolate (L. monocytogenes 4b). In addition, for all the isolates tested the binary interaction between eugenol and limonene impacted significantly (p <0.05) the reduction of the population of L. monocytogenes, therefore the existence of synergism between these two compounds was confirmed. Acknowledgements: FAPESP and CNPq.