Study On The Effect Of Listeria Monocytogenes' Activity Of Cold Meat In Cold Chain Circulation

Listeria monocytogenes is a common pathogenic bacteria,which widely exists in nature.It can be found in soil,surface water,plants,human and animal feces,and foods.In recent years,there has been a series of food poisoning incidents.The incidence of Listeria monocytogenes is increasing.It has also attracted the attention of food safety experts and public health workers.In the process of meat production and transportation,the meat has been cold treatment,although the meat has been in a low temperature control,it is still inevitable with microorganisms.So unless the correct processing,packaging,storage and transportation,cold meat is very susceptible to microbial contamination.The study shows that Listeria monocytogenes is one of the pathogenic bacteria which are easily infected in cold chain of the cold meat.In this study,through using predictive model of microbiology,studying the growth of Listeria monocytogenes in different storage conditions of cold meat,and food distribution in the real environment with the change of temperature,humidity and other environmental factors that may occur,mathematical model was established to predict growth and survival of Listeria monocytogenes under specific conditions.The main results of the stydy are as follows: 1.Identification of Listeria monocytogenesListeria genus contains 6 species,Listeria ivanovii is the main cause of ruminant animal infection,Listeria monocytogenes is the main pathogens of people and animals.lineage III of Listeria monocytogenes rarely cause disease.Comparative genomics analysis showed that the cell wall hydrolase gene IAP existed in various species of Lester bacteria and had both ends conservative regions and intermediate variable regions.The lmo0029-0042 region has a different gene arrangement in Lester bacteria of various species,lmo0038 exists in pathogenic Lester bacteria(Listeria monocytogenes I and II,and Listeria ivanovii).2.Detection and application of multiple PCR detection system in fresh pork200 cold fresh meat samples were collected from Hangzhou market.The detection rate of pathogenic bacteria was 21%.The detection rate of pathogenic bacteria in cold fresh pork(24.7%)was significantly higher than that of fresh pork (10%)at normal temperature.Detection rate of Listeria monocytogenes at room temperature in fresh pork was 2%,and in the cold fresh pork was 14.7%.3.Study on the prediction model of Listeria monocytogenes during cold chain circulationWith the increasing of temperature,the stagnation period of LM growth in raw pork gradually shortened.LPD is 272.4h,53.9h and 2.6h at 4?,8? and 12?,and there is almost no stagnation period at 16?.GR gradually increases with the increasing of temperature.It is 0.014(log(cfu/g).h-1 at 4?,0.056(log(cfu/g).h-1 at 16?.In the temperature range of 4-16?,the change of MPD has no obvious rule,and it is between 7.20 log(cfu/g)-8.28 log(cfu/g).The prediction value given by model GP is higher than the measured value except 4 ?.on the contrary,The prediction value given by model CP is lower than the measured value except 4 ?.The predicted value of PMP in the whole temperature range is lower than the measured value,but it is higher than the predicted value of CP.4.Study on the inactivation model of Listeria monocytogenes' growth in pork by dealing with organic acidsFoodborne pathogens are more sensitive to organic acids in normal saline,and the sterilizing effect in food matrix is relatively low,which shows that matrix has a significant effect on the inhibition of organic acids.Compared with the total concentration of organic acids,the inhibitory ability of citric acid is the strongest, the lactic acid is the second,and the acetic acid is the weakest.But in organic acid spray experiment,the inhibitory ability of lactic acid with 2.5%(m/v)concentration was higher than citric acid.