Construction Of Predictive Growth And Inhibition Model Of L.Monocytogenes In Fresh-Cut Iceberg Lettuce

L.monocytogenes is a very popular foodborn pathogen that often reported in recent years, and World Health Organization (WHO) has listed it as the1990s one of the four major foodborne pathogens. L.monocytogenes can cause, including fresh vegetables and other plant foods contamination, it can grow in the low-temperature, acidic, high-salt environment. L.monocytogenes has caused several food safety incidents in European countries, and the mortality rate reached30%.In virtue of predictive microbiology, we can make a quick evaluation for shelf life and quality of product without traditional test. This paper studies the growth of L. monocytogenes in liquid medium and fresh-cut iceberg lettuce, predictive models were established respectively and the and deviation between the two were compared.Combined with low-temperature atmosphere packaging technology, the growth inhibition effect of Listeria monocytogenes on the fresh-cut iceberg lettuce by different concentrations of CO2was studied, and the inhibitory models were established. The results are as follows:1. The basic growth characteristics of Listeria monocytogenes were studied, the results show that L. monocytogenes optimum growth temperature is30-40℃, the optimum growth pH is7-8, the optimum growth water activity is0-1%(NaCl concentration).2. The liquid medium and fresh-cut iceberg lettuce were inoculated by L. monocytogenes respectively at4,8,16,24,32℃for storage.The status of growth at different temperatures was compared to modified Gompertz model with Sigmaplot program, the results showed that growth dynamics of Listeria monocytogenes at different temperatures could be well described by Gompertz model.The correlation regression of Belehradek model finely described the temperature on specific growth rate (μmax) and lag phase (λ).But the model based on liquid medium can not accurately predict the growth of L. monocytogenes on fresh-cut iceberg lettuce, there are significant differences between the two models.3. Using fresh-cut iceberg lettuce as test materials, effects of different CO2concentration combined10%O2on storage quality of fresh-cut iceberg lettuce at low temperature were investigated.The results showed that high concentrations of CO2did signifcicant impact on strorage quality.Combined sensory evalution results, compared with the control group, high concentrations of CO2treatment extended the shelf of fresh-cut iceberg lettuce about3-9days.4. The fresh-cut iceberg lettuce were inoculated by L. monocytogenes at4-32℃and10-50%CO2concentrations for storage.The status of growth at different temperatures and CO2concentrations was compared to modified Gompertz model with Sigmaplot program,the results showed that growth of Listeria monocytogenes at different temperatures and CO2concentrations could be well described by Gompertz model.The secondary model of Listeria monocytogenes grown at different temperatures and CO2concentrations was established by using Matlab7.1toolbox fmincon nonlinear optimal value function.Bias and accuracy factors were calculated respectively,it suggested in the range of temperature4-32℃,10-50%CO2,the model we built can predict the growth of Listeria monocytogenes in fresh-cut iceberg lettuce.