A MODEL DESCRIBING THE RELATIONSHIP BETWEEN LAG TIME AND MILD TEMPERATURE INCREASE DURATION

When a bacterial population undergoes an unfavourable increase in temp erature for a given duration, called stress duration, a death phase fo llowed by a lag and a growth phase are observed. The lag phase is actu ally of great interest in regard to foodstuff safety in choosing a sui table protocol for the detection of microorganisms which have undergon e a mild heat treatment. The extension of lag time with the severity o f the increase in temperature has been highlighted by previous papers. Our experimental results concerning Listeria monocytogenes and Escher ichia coli revealed that a two phase relationship between lag time and stress duration is observed for a specific increase in temperature. T he first phase consists of an increase in lag time up to a peak; the s econd one consists of a decrease from this peak to a steady threshold. The mathematical model presented, describing the relationship between lag time and stress duration was empirically built from our experimen tal data concerning L. monocytogenes and E. coli. The fit evaluation c arried out led us to consider this model as a good description of the relationship studied. The potential contribution of our model in heat treatment optimization is discussed. (C) 1997 Elsevier Science B.V.