Effect of thymol and cymene on Bacillus cereus vegetative cells evaluated through the use of frequency distributions

The bactericidal action of thymol and cymene on two Bacillus cereus strains (INRA-AVTZ415 and INRA-AVZ421) was studied. Increasing concentrations of thymol (0.2-1.0 mmol l(-1)) or cymene (0.2-2.0 mmol l(-1)) showed higher bactericidal effect on exponential growth phase B. cereus cells suspended in HEPES buffer (pH 7), at 30degreesC. The two strains tested presented different sensitivity to these natural antimicrobials. When thymol and cymene were combined, it resulted in a greater bactericidal effect on B. cereits cells than when these compounds in the essential oil fraction of aromatic plants were applied separately. There was a synergistic effect of both natural antimicrobials on the viability of exponential growth phase B. cereus cells in pH 7 HEPES buffer, at 30degreesC. Survivor curves did not follow a first-order kinetics, which makes it difficult to establish processing conditions. Experimental data were modeled using a frequency distribution function (Weibull). This model guaranteed a good description of the experimental results and allowed predictions of time to a specific decrease in bacterial populations. This study indicates the potential use of thymol and cymene applied separately or simultaneously for preservation of minimally processed foods, as well as the validity of the Weibull distribution to describe the resulting nonlinear data and establish effective treatment conditions with these compounds. (C) 2003 Elsevier Ltd. All rights reserved.