MODELING OF BACTERIAL-GROWTH WITH SHIFTS IN TEMPERATURE

The temperature of chilled foods is an important variable for the shel f life of a product in a production and distribution chain. To predict the number of organisms as a function of temperature and time, it is essential to model the growth as a function of temperature. The temper ature is often not constant in various stages of distribution. The obj ective of this research was to determine the effect of shifts in tempe rature. The suitability and usefulness of several models to describe t he growth of Lactobacillus plantarum with fluctuating temperatures was evaluated. It can be assumed that temperature shifts within the lag p hase can be handled by adding relative parts of the lag time to be com pleted and that temperature shifts within the exponential phase result in no lag phase. With these assumptions, the kinetic behavior of temp erature shift experiments was reasonably well predicted, and this hypo thesis was accepted statistically in 73% of the cases. Only shifts of temperature around the minimum temperature for growth showed very larg e deviations from the model prediction. The best results were obtained with the assumption that a temperature shift (within the lag phase as well as within the exponential phase) results in an additional lag, p hase. This hypothesis was accepted statistically in 93% of the cases. The length of the additional lag phase is one-fourth of the lag time n ormally found at the temperature after the shift.