Predictive modelling of Listeria monocytogenes in Irish smoked salmon

The effect of four storage temperatures on the simultaneous growth of Listeria monocytogenes and food flora in vacuum packed cold-smoked salmon was investigated. The growth data (log(10) CFU g(-1)) of all the bacteria at 4, 10, 17 and 24 degrees C were modelled as a function of time using DM-Fit (Baranyi and Roberts, 1994) and the kinetic parameters such as maximum specific growth rate (mu(max)), lag phase (lambda) and maximum population density (MPD) were obtained. This investigation shows that Listeria monocytogenes grows in vacuum packed smoked salmon held at 24 to 4 degrees C with colony fori-ning units ranging from a minimum of 1.2cfu/g at 4 degrees C and a maximum of 8.21cfu/g at 24 degrees C showing a six-fold increase from the minimum value after a period of 18 days. The growth data of the food flora showed that Lactic acid bacteria grew well in all temperatures studied and showed an 8-fold increase after 18 days at 24 degrees C, while the mesophils grew well at 24 degrees C and reached up to 10(9) log(10) CFU g(-1) and the psycrophils grew well at 4 and 10 degrees C reaching up to 10(4)log(10) CFU g(-1) after 18 days. The Arrhenius and square root models were used to describe the effect of different storage temperature on mu(max). The effect of the temperature was better interpreted by the Arrhenius type model. When kinetic parameters were compared with the predictive models - Com Base Predictor and Pathogen modelling programme (PMP) - the experimental data were in line with the predictive models at 4 and 10 degrees C.