Growth/no growth interface of Brochothrix thermosphacta as a function of pH and water activity Original Research Article

A growth/no growth boundary model based on interpolated probabilities is presented in this paper. The boundary is defined as the loci where the probability of growth for a sample is equal to its chance of no growth, P (growth)=P (no growth). Brochothrix thermosphacta was used as a test micro-organism to collect data near the boundary of growth/no growth, in a pH/NaCl grid. Results showed a dramatic change in the probability of growth at the boundary with minor changes of pH or NaCl, and that the location of the boundary was affected by the inoculum level. A quadratic polynomial was used to describe the boundary of the growth region (interpolated P=0·5). The importance of growth/no growth boundary models as limits for the application of kinetic models is discussed.