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Applied and Environmental Microbiology, November 2009, p. 6992-6997, Vol. 75, No. 22
0099-2240/09/$08.00+0     doi:10.1128/AEM.00452-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Analysis of the Variability in the Number of Viable Bacteria after Mild Heat Treatment of Food{triangledown}

J. S. Aguirre,1 C. Pin,2* M. R. Rodríguez,1 and G. D. García de Fernando1

Departamento de Nutrición, Bromatología y Tecnología de los Alimentos, Facultad de Veterinaria, Universidad Complutense, Ciudad Universitaria, Madrid 28040, Spain,1 Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, United Kingdom2

Received 24 February 2009/ Accepted 23 September 2009

Variability in the numbers of bacteria remaining in saline solution and whole milk following mild heat treatment has been studied with Listeria innocua, Enterococcus faecalis, Salmonella enterica serovar Enteritidis, and Pseudomonas fluorescens. As expected, the most heat-resistant bacterium was E. faecalis, while P. fluorescens was the least heat resistant, and all bacteria showed greater thermal resistance in whole milk than in saline solution. Despite the differences in the inactivation kinetics of these bacteria in different media, the variability in the final number of bacteria was affected neither by the species nor by the heating substrate, but it did depend on the intensity of the heat treatment. The more severe the heat treatment was, the lower the average number of surviving bacteria but the greater the variability. Our results indicated that the inactivation times for the cells within a population are not identically distributed random variables and that, therefore, the population includes subpopulations of cells with different distributions for the heat resistance parameters. A linear relationship between the variability of the log of the final bacterial concentration and the logarithmic reduction in the size of the bacterial population was found.

* Corresponding author. Mailing address: Institute of Food Research, Norwich Research Park, Norwich NR4 7UA, United Kingdom. Phone: 441603255000. Fax: 441603255288. E-mail: carmen.pin{at}bbsrc.ac.uk

{triangledown} Published ahead of print on 2 October 2009.

Applied and Environmental Microbiology, November 2009, p. 6992-6997, Vol. 75, No. 22
0099-2240/09/$08.00+0     doi:10.1128/AEM.00452-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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