[Probability of growth initiation of listeria spp in a model broth as affected by species, pH, temperature, sodium chloride, potassium sorbate and storage time]

ABSTRACT

The effects of NaCL [0.5, 4.0, 7.5%] potassium sorbate [KS, 0.0, 0.15, 0.3%], pH [5.9, 5.3], temperature [T,4,8,20,30 C], time [D, up to 58-68d] and inoculum [10-2107 on the log10 probability percentage [P] of one cell L. monocylogenes, L.innocus, L.ivanoviii to initiate growth in brain heart infusion broth were evaluated in a factorial design study. The P of L monocytogenes was affected significantly [0.0001 pH, T, NaCL, KS, D, and TxpH, TxKS, pHxKS, NaCLxKS, TxpHxKS, TxNaClxKS and pHxNaClxKS interactions. The P decreased by increasing concentration of KS, NaCL, and decreasing pH and T and prolonging storage. The bacteriostatic effect of pH, KS and NaCL was enhanced and the bactericidal effect was diminished with the decreasing of T. L. ivanovii was the most and L. monocytogenes the least sensitive species to the inhibitory effect of the variables studied. There was a concentration dependent antagonism of NaCL [4%] on KS action. Therefore a particular caution may be needed in high ph foods with a moderate salt concentration preserved with sorbate. Regression equations were derived relating P to NaCL, KS, pH, T and D. From the equations, the number of cells needed to initiate grown can be calculated