Purpose: To evaluate the synergistic effects of clove (C) and lemon (L) essential oils by determining the minimum inhibitory concentration against Listeria monocytogenes strains.
Methods: The minimum inhibitory concentration (MIC) was determined by using the broth dilution method for testing six isolates of L. monocytogenes (ATCC 35152 and five isolates from meat products). Each culture (106 CFU/mL) was inoculated in 5 mL tryptic soy broth plus yeast extract (TSB-YE) tubes containing different concentrations of the essential oils. After 24h at 37 ± 1° C, 100 μL of each tube was spread plated on the surface of trypticase soy agar plus-YE and incubated for 37 ± 1° C for 24 h. Positive and negative controls were used. After determining the MIC, the essential oil fractions were mixed at different proportions (100, 75/25, 50/50, 50/25, 25/25%, v/v) in which 100% was the MIC obtained for each oil. The presence or absence of colonies using the broth dilution method was tested.
Results: The L. monocytogenes ATCC 35152 was the most sensitive against both essential oils evaluated with MIC values of 0.05 and 0.2% for clove and lemon essential oils, respectively. For all other strains, the MIC value was higher - 0.1 and 0.3% - respectively, for those essential oils. The inhibitory effect was also achieved by using a combination of 75/25 (C/L), 50/50 (C/L), 50/25 (C/L) and 75/25 (L/C).
Significance: The results showed the synergistic effects between fractions of clove and lemon essential oils tested against L. monocytogenes strains. The combination of essential oils can reduce the concentrations used and therefore minimizing sensorial impact in food.