Modelling the influence of temperature and carbon dioxide upon the growth of Pseudomonas fluorescens

Abstract

Pseudomonas fluorescens was chosen as an indicator micro-organism for spoilage of ready-to-eat or Grade IV leafy vegetables. The effect of the extrinsic storage conditions (temperature and carbon dioxide concentration) upon the growth in a model system were studied. The bacterial growth curve was described with the logisitic and Gompertz equation. These sigmoidal functions were modified to give the lag time and maximum absolute growth rate for P. fluorescens under controlled storage conditions. In a temperature range of 4 to 12°C the lag time of P. fluorescens showed an exponential dependence with temperature, whereas a linear relationship of the maximum absolute growth rate with temperature was observed. Carbon dioxide was shown to be effective against the proliferation of aerobic psychrotrophic Gram-negative bacteria by principally increasing the lag phase and to a lesser extent the generation time. The dependence of the lag time and the maximum absolute growth rate of P. fluorescens with the carbon dioxide concentration (0·03-15%, with an excess of oxygen) was described using an exponential function. Moreover, the effectiveness of the inhibition increased with decreasing temperatures.