Comparison of growth models of Listeria monocytogenes in chilled pork

Abstract:

Abstract:［Objective］To investigate the growth of Listeria monocytogenes (LM) in chilled pork at four temperature and to evaluate the accuracy of three predictive models- GP (Growth Predictor)，PMP(Pathogen Modeling Programme) and CP (ComBase Predictor) in predicting LM growth in chilled pork． ［Methods］ LM growth in chilled pork at 4℃，8℃，12℃ and 16℃ were determined by plate counting． The growth data were fitted by DMFit software to calculate related growth parameters: lag phase duration (LPD)，growth rate (GR) and maximum population density (MPD)．The observation values and predictions of the three different models were compared． ［Result］LM grew into exponential phase after 2. 6 hours of adaptation at 16℃ ． A four- degree increase from 8℃ to 12℃ doubled GR from 0.017 log(cfu/g)．h－1 to 0.038log(cfu/g)．h－1)．Over the temperature span from 4℃ to 16℃，GR values predicted by PMP were lower than observations，while those of LPD higher than observations． At temperature above 8℃ ，LPD values predicted by GP were higher than observations．Of three predictive models，GP prediction of GR was the best，though slightly higher than observations，with the bias factor (Bf) at 1.01 and accuracy factor (Af) at 1. 38，while CP was nearest to observations for LPD prediction，but still with high values of Af and Bf (4.33 and 2.83 respectively)．［Conclusion］ It is of utmost importance to control temperature in chilled pork production and distribution． Because of the conservative but unsafe predictions，PMP model is not suitable for prediction of LM in chilled pork． We suggest to use GP for GR prediction． CP may be used to predict LPD as a reference，but with caution．