Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 1/23/2006
Publication Date: 6/1/2006
Citation: Abou-Zeid, K.A., Yoon, K.S., Schwarz, J.G., Oscar, T.P., Hashem, F.M., Whiting, R. 2006. Development and validation of primary and secondary models for lag time and specific growth rate of listeria monocytogenes scott a in broth. [Abstract] American Society for Microbiology Annual Meeting. Interpretive Summary:
Technical Abstract: Kinetic data for development of models that predict growth of pathogens in sterile broth are widely used by food industries and risk assessors to evaluate food safety. However, establishment of criteria for acceptable prediction values are needed to determine whether a model provides valid predictions of pathogen growth. In this study, we developed and validated models for the effects of temperature (4-37C), pH (5.5-7.0), and lactate/diacetate mixtures (0-3.0%) on lag time (LT) and specific growth rate (SGR) for L. monocytogenes in broth. Models were evaluated for model performance using the prediction bias (Bf) and accuracy factors (Af), and the acceptable prediction zone method (%RE). One-hundred twenty primary growth curves were fitted using the Baranyi model that directly estimated LT and SGR. The effects of the variables on L. monocytogenes growth kinetics were modeled by response surface analysis using quadratic and cubic polynomial models of the natural logarithm transformation of both LT and SGR. All models provided reasonable estimates for most combinations of variables. Comparison of predicted versus observed values of SGR indicted that the cubic model was better than the quadratic model; particularly at 4 and 10C. The Bf and Af for cubic and quadratic models were 1.03, 1.09, and 0.97, 1.19, respectively. These results indicated that both models show fail-safe predictions for SGR. For cubic and quadratic models, the %RE for the dependent data in the acceptable prediction zone was 92.9 and 74.7, respectively. For the independent data, the %RE were 92.6 for the cubic model and 81.2 for quadratic model. Although cubic and quadratic models were developed for LT, the cubic model did not predict LT better than the quadratic model with %RE of 83.8 and 81.5 for the dependent and independent data, respectively. The Bf of 1.07 and Af of 1.17 were obtained for both models, indicating fail-safe predictions for LT. Overall, these results indicate that the secondary, quadratic and cubic polynomial models for LT and SGR provided acceptable predictions of L. monocytogenes growth in broth as a function of temperature, pH, and lactate/diacetate concentration.