Four mathematical models were developed and validated for simultaneous growth of mesophilic lactic acid
bacteria from added cultures and Listeria monocytogenes, during chilled storage of cottage cheese with freshor
cultured cream dressing. The mathematical models include the effect of temperature, pH, NaCl, lactic- and
sorbic acid and the interaction between these environmental factors. Growthmodels were developed by combining
new and existing cardinal parameter values. Subsequently, the reference growth rate parameters (μref at
25 °C)were fitted to a total of 52 growth rates fromcottage cheese to improvemodel performance. The inhibiting
effect of mesophilic lactic acid bacteria from added cultures on growth of L. monocytogenes was efficiently
modelled using the Jameson approach. The new models appropriately predicted the maximum population
density of L. monocytogenes in cottage cheese. The developed models were successfully validated by using 25
growth rates for L. monocytogenes, 17 growth rates for lactic acid bacteria and a total of 26 growth curves for simultaneous
growth of L. monocytogenes and lactic acid bacteria in cottage cheese. These data were used in combination
with bias- and accuracy factors and with the concept of acceptable simulation zone. Evaluation of
predicted growth rates of L. monocytogenes in cottage cheese with fresh- or cultured cream dressing resulted
in bias-factors (Bf) of 1.07–1.10with corresponding accuracy factor (Af) values of 1.11 to 1.22. Lactic acid bacteria
fromadded starter culturewere on average predicted to grow16% faster than observed (Bf of 1.16 and Af of 1.32)
and growth of the diacetyl producing aromaculturewas on average predicted 9% slower than observed (Bf of 0.91
and Af of 1.17). The acceptable simulation zone method showed the new models to successfully predict maximum
population density of L. monocytogenes when growing together with lactic acid bacteria in cottage cheese.
11 of 13 simulations of L.monocytogenes growth were within the acceptable simulation zone,which demonstrated
good performance of the empirical inter-bacterial interaction model. The new set of models can be used to
predict simultaneous growth of mesophilic lactic acid bacteria and L. monocytogenes in cottage cheese during
chilled storage at constant and dynamic temperatures. The appliedmethodology is likely to be applicable for safety
prediction of other types of fermented and unripened dairy productswhere inhibition by lactic acid bacteria is
important for growth of pathogenic microorganisms.
Four mathematical models were developed and validated for simultaneous growth of mesophilic lactic acidbacteria from added cultures and Listeria monocytogenes, during chilled storage of cottage cheese with freshorcultured cream dressing. The mathematical models include the effect of temperature, pH, NaCl, lactic- andsorbic acid and the interaction between these environmental factors. Growthmodels were developed by combiningnew and existing cardinal parameter values. Subsequently, the reference growth rate parameters (μref at25 °C)were fitted to a total of 52 growth rates fromcottage cheese to improvemodel performance. The inhibitingeffect of mesophilic lactic acid bacteria from added cultures on growth of L. monocytogenes was efficientlymodelled using the Jameson approach. The new models appropriately predicted the maximum populationdensity of L. monocytogenes in cottage cheese. The developed models were successfully validated by using 25growth rates for L. monocytogenes, 17 growth rates for lactic acid bacteria and a total of 26 growth curves for simultaneousgrowth of L. monocytogenes and lactic acid bacteria in cottage cheese. These data were used in combinationwith bias- and accuracy factors and with the concept of acceptable simulation zone. Evaluation ofpredicted growth rates of L. monocytogenes in cottage cheese with fresh- or cultured cream dressing resultedin bias-factors (Bf) of 1.07–1.10with corresponding accuracy factor (Af) values of 1.11 to 1.22. Lactic acid bacteriafromadded starter culturewere on average predicted to grow16% faster than observed (Bf of 1.16 and Af of 1.32)
and growth of the diacetyl producing aromaculturewas on average predicted 9% slower than observed (Bf of 0.91
and Af of 1.17). The acceptable simulation zone method showed the new models to successfully predict maximum
population density of L. monocytogenes when growing together with lactic acid bacteria in cottage cheese.
11 of 13 simulations of L.monocytogenes growth were within the acceptable simulation zone,which demonstrated
good performance of the empirical inter-bacterial interaction model. The new set of models can be used to
predict simultaneous growth of mesophilic lactic acid bacteria and L. monocytogenes in cottage cheese during
chilled storage at constant and dynamic temperatures. The appliedmethodology is likely to be applicable for safety
prediction of other types of fermented and unripened dairy productswhere inhibition by lactic acid bacteria is
important for growth of pathogenic microorganisms.
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