Inactivation Of High Pressure Treatment On Listeria Monocytogenes In Cooked Ham

High pressure processing (HPP), which is a non-thermal processing technology, causes micro-organisms in food to be inactivated or killed at higher pressures to extend shelf life, but with little or no effects on nutritional or quality parameters. Because of these unique advantages, HPP is more and more got attention by food industry and consumers.Low temperature meat products is referred to that meat products are processed with low temperatures (68-85℃), and production, transportation, and sale of cooked meat are at low temperatures. Low temperature meat products maintain more nutrition and flavour properties to greatest extent with advanced procedure and wide markets, which orient the future meat industry. Due to low-temperature heating process and recontamination during slicing and packaging procedures, low temperature meat products are subjected to Listeria monocytogenes,.which widely exist in nature with environmental adaptability and highly pathogenic. it is harm to food safety. High pressure treatment can effectively inhibit Spoilage and pathogenic microorganisms in the low temperature meat products. Now, HPP is being used commercially in a number of developed countries. However, in our country, high pressure technology still in the initial stage, It limit the development of low temperature meat products. This research object is Listeria monocytogenes in sliced vacuum-packaged smoked ham as model system. The physiological state of Listeria monocytogenes after high pressure processing was investigated to further study HPP lethal effects on Listeria monocytogenes. Based on it, Listeria monocytogenes growth prediction model, which is treated HPP combined heating in sliced vacuum-packaged smoked ham during storage was established. We would like to provide a theory basis and techniques guidance for quality and safety assurance of low temperature meat products. The whole work includes five parts, the specific contents and results are as follows:1. Effects on Physiological States of Listeria monocytogenes after high pressure processingTo reveal antibacterial mechanism by studying the change of physiological states of Listeria monocytogenes after high pressure treatment. In this experiment, it was analyzed that the effect on Listeria monocytogenes survival, cell morphology, cell membrane integrity and esterase activity after high pressure treatment through different culture counting method, transmission electron microscopy and flow cytometry parameters. The results showed that after HPP a part of Listeria monocytogenes were in the injured state, these injured microorganisms could be repaired to grow in optimal conditions. High pressure treatment destroyed Listeria monocytogenes cell membrane, but the impact of esterase activity was not significant; It was a milder measure than the traditional high-temperature sterilization. it didn’t cause to serious damage of the bacterial shape, but It got entoenzyme constituting by proteins degenerate or other functional ingredients affected seriously, which resulted in the disorder of the biochemical reactions within the cell to achieve the effect of inhibition of microbial.2. Inactivation model of Listeria monocytogenes in cooked ham by high pressure processingIn this part, cooked ham as the matrix, selection pressure, pressure holding time and temperature on high pressure processing inactivation of Listeria monocytogenes were investigated by single factor method. Response surface methodology (RSM) was then employed and a second order quadratic equation for high pressure processing inactivation was built base on these three factors. The adequacy of the model equation for predicting the optimum response values was verified effectively by the validation data. By analyzing the response surface plots and their corresponding contour plots as well as solving the quadratic equation, the optimum process parameters for inactivation of Listeria monocytogenes of four log cycles were obtained as:pressure426.75MPa, pressure holding time12.19min and processing temperature under39.20℃.3. Predictive modeling of the recovery of Listeria monocytogenes on cooked smoked ham after high pressure combined with different temperature processingIn this part, to establish suitable predictive model for the recovery of Listeria monocytogenes on cooked smoked ham after high pressure combined with different temperature processing. Cooked smoked ham, inoculated with106cfu/g Listeria monocytogenes, was subjected to high pressure treatments at600MPa for5min combined with20,30,40and50℃, respectively, and then stored at4℃, counts of Listeria monocytogenes were determined every10days after treatment. It was found that the treatment temperature higher than40℃combined with high-pressure efficiently prolong self-repairing growth postponing period of Listeria monocytogenes in sliced vacuum-packaged smoked cooked ham. The growth curve of Listeria monocytogenes was imitated by modified Gompertz type model and validated at35and45d, respectively, to establish a growth predictive model of Listeria monocytogenes in sliced vacuum-packaged smoked cooked ham treated by high pressure and temperature. After validation of the model, the results of Af, Bf, RMSE and R2were proved to be in a proper range. Consequently, the result suggests that the model could well imitate growth condition of Listeria monocytogenes and it could provide a theory basis of Listeria monocytogenes control in low-temperature meat product.