Use of Frequency Distribution Functions to Establish Safe Conditions in Relation to the Foodborne Pathogen Bacillus cereus

Begoña Delgado1, Paula M. Periago2, Raquel Conesa1, Alfredo Palop1 and Pablo S. Fernández1*

Unidad Asociada UPCT-IATA (CSIC), Dpto. Ing. Alimentos y del Equipamiento Agrícola, Paseo Alfonso XIII 48, E-30203 Cartagena, Murcia, Spain

2Centro de Edafología y Biología Aplicada del Segura (CEBAS-CSIC), Dpto. Ciencia y Tecnología de Alimentos, Murcia, Spain

Article history:

Received September 3, 2004
Accepted February 28, 2005

Key words:

Bacillus cereus, natural antimicrobials, frequency distributions


Minimal processing implementation greatly depends on a detailed knowledge of the effects of preservation factors and their combinations on the spoilage and foodborne pathogenic microorganisms. The effectiveness of mild preservation conditions will become increasingly dependent on a more stochastic approach linking microbial physiological factors with product preservation factors. In this study, the validity of frequency distributions to efficiently describe the inactivation and growth of Bacillus cereus in the presence of natural antimicrobials (essential oils) has been studied. For this purpose, vegetative cells were exposed to 0.6 mM of thymol or cymene, obtaining survival curves that were best described by the distribution of Weibull, since a tailing effect was observed. B. cereus was also exposed in a growth medium to a low concentration (0.1 mM) of both antimicrobials, separately or combined, and the lag times obtained were fitted to a normal distribution, which allowed a description of dispersion of the start of growth. This allowed a more efficient evaluation of the experimental data to establish safe processing conditions according to accurate parameters and their implementation in risk assessment.

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