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Applied and Environmental Microbiology, July 2002, p. 3432-3441, Vol. 68, No. 7
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.7.3432-3441.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Modeling the Interactions of Lactobacillus curvatus Colonies in Solid Medium: Consequences for Food Quality and Safety

P. K. Malakar,1,2* D. E. Martens,2 W. van Breukelen,2 R. M. Boom,2 M. H. Zwietering,3 and K. van 't Riet4

Institute Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, United Kingdom,1 Danone Vitapole, 92350 Le Plessis Robinson, France,3 Stategie en programma TNO, 2600 JA Delft,4 Department of Food Technology and Nutritional Sciences, Food and Bioprocess Engineering Group, Wageningen University, 6700 EV Wageningen, The Netherlands2

Received 19 November 2001/ Accepted 10 April 2002

The growth process of Lactobacillus curvatus colonies was quantified by a coupled growth and diffusion equation incorporating a volumetric rate of lactic acid production. Analytical solutions were compared to numerical ones, and both were able to predict the onset of interaction well. The derived analytical solution modeled the lactic acid concentration profile as a function of the diffusion coefficient, colony radius, and volumetric production rate. Interaction was assumed to occur when the volume-averaged specific growth rate of the cells in a colony was 90% of the initial maximum rate. Growth of L. curvatus in solid medium is dependent on the number of cells in a colony. In colonies with populations of fewer than 105 cells, mass transfer limitation is not significant for the growth process. When the initial inoculation density is relatively high, colonies are not able to grow to these sizes and growth approaches that of broth cultures (negligible mass transfer limitation). In foods, which resemble the model solid system and in which the initial inoculation density is high, it will be appropriate to use predictive models of broth cultures to estimate growth. For a very low initial inoculation density, large colonies can develop that will start to deviate from growth in broth cultures, but only after large outgrowth.

* Corresponding author. Mailing address: Institute Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, United Kingdom. Phone: 44 1603 255141. Fax: 44 1603 507723. E-mail: pradeep.malakar{at}bbsrc.ac.uk.

Applied and Environmental Microbiology, July 2002, p. 3432-3441, Vol. 68, No. 7
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.7.3432-3441.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.





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