Mathematical tools for objective comparison of microbial cultures: Application to evaluation of 15 peptones for lactic acid bacteria productions

Using the logistic model as a starting point, a set of reparameterised equations were established which permit the easy calculation of the relevant parameters of microbial kinetics, together with their confidence limits, with the aim of establishing rigorous comparison between cultures under differing conditions. When the resource was used to evaluate the aptitude of peptones from diverse sources for the culture of lactic acid bacteria (LAB), a great variability was found, even among the results of commercial formulations with the same denomination. None of the peptones was able to maximise the growth – very active in fish peptones – and the production of the characteristic metabolites at the same time. Under these conditions, the application of the cluster analysis to kinetic parameters of proven descriptive capability becomes a useful exploratory method, which allows to decide combinations of protein sources apt to make compatible different potential purposes of LAB cultures. This way, it is possible to design factorial experiments to search optimum values for these purposes on the basis of hypothesis which avoid the selection of superfluous variables and inadequate domains.