| Vacuum-packed Zhenjiang Yao meat is a marinated-jellied pork product which is produced by using modern low-temperature meat processing technology. It is easily contaminated by microorganisms due to different sources and rich nourishment of raw materials. The low-temperature sterilization process can endue Zhenjiang Yao meat quality problems, which not only limit the shelves and sales radius, but also affect the scale of production of the meat processing enterprises. To solve the problem is to establish the research methods and control technology according to the spoilage microorganisms in vacuum-packed Zhenjiang Yao meat.The vacuum-packed Zhenjiang Yao meat should be storaged under low temperature, has short shelf life and easily become perishable deterioration, which is dued to indigenous microorganisms. In this study, the microbial diversity and dynamic main flora of the meat were determined and a natural, safe, efficient antibacterial agent used to control the specific meat dish special spoilage organisms (SSO) was developed using the natural products. The antibacterial mechanism of the agent was investigated to understand its effectiveness controlling the quality and safety of vacuum-packed Zhenjiang Yao meat. The main research contents and results are as follows:(1) The storage characteristics of vacuum-packed Zhenjiang Yao meat produced in different seasonswere studied under4℃by sensory evaluation, pH value, AW, TVB-N, TBARS and microbial quantity determination. The results reveal that:First, the nitrite content increased firstly, then downward. The highest content of nitrite appears on the seventh day, but the nitrite content is still among the safty range for eating during the shelf life.Second, the sensory quality of Yao meat mainly become worse as like pale flesh, off-odor, cloudy, moist surface and looses structure, which is caused by the action of microorganisms made degradation of protein and amino acids.Third, the pH value of Yao meat become downward slowly within the extension of storage. The AW and TBARS values changed little during storage, indicating Aw and fat oxidation were not the main cause of Yao meat spoilage. During storage, the TVB-N value showed a upward trend. Products producd in summer and autumn season became quickly spoilage and were not edible after the30d’s shelf life, indicating microbial growth and its action on protein degradation as the major factors to cause spoilage.Fourth, the numbesr of microorganisms showed overall upward trend. Products producd in winter harboured the lowest total number of bacteria in the early stages, the total number of bacteria was105cfu/g at the end of storage. Summer samples had the highest total number of bacteria in the early stages of storage, and the growth rate was fastest during the storage period, the total number of bacteria reached108cfu/g at the end of storage. Samples in spring and autumn had a slightly lower total number of bacteria than that of the summer sample, whose maximum number of colonies was107cfu/g. During storage, the main groups were Pseudomonas and Enterobacteriaceae.Fifth, producing seasons had a direct impaction on the storage characteristics of vacuum-packed Zhenjiang Yao meat. Summer’s samples had the lowest pH value, the highest TVB-N value, and the highest total number of bacteria at the end of storage.(2) Bacterial diversity and dynamic populations under4℃in30days were determined using a combination of culture-independent (454pyrosequencing) and Cultivation methods. The results showed that:First, bacterial isolates of26genera and36species were cultivated from vacuum-packed Zhenjiang Yao meat during storage, among which Vibrio rumoiensis was the main group at the early storage period. Lactobacillus sakei was the main microorganism at the middle storage; Enterococcus faecium, Yersinia intermedia and Psychrobacter glacincola were the main microorganisms at t the end of storage.Second, phylotypes of one hundred and sixty-nine genera were identified and53,363tags were obtained by454Pyrosequencing method. Vibrios were the main flora at0d,7d and30d, while Lactobacillus and Yersinia were the main flora at15d,22d and30d. All of the samples had different bacterial communities. The bacterial community changed greatly after15days of storage, and the bacterial communities at30d differed significantly from the other samples.Third, Pyrosequencing provide a more comprehensive estimatination of microbial diversity and closer to the real bacterial composition of meat compared with culture-dependent techniques.(3) the quality changes of vacuum-packed Zhenjiang Yao meat during storage were investigated by inoculating five dominant bacteria in samples.. The results showed that:First, Yersinia intermedia, Enterococcu faeciums and Lactobacillus sakei can grow rapidly in samples can increase the rate of fat oxidation and protein degradation. These bacteria were the SSO that cause the spoilage of vacuum-packed Zhenjiang Yao meat.Second, the SSO of vacuum-packed Zhenjiang Yao meat were tracked by sampling at different production links,and then analyses using denaturing gradient gel electrophoresis. The results showed that:Yersinia intermedia and Enterococcus faecium were presented in raw pork materials and can be killed in the cooking process. However, Yao meat may be contaminated by the two bacteria in the subsequent briquetting and packaging process. Lactobacillus sakei occurring in samples after cooking revealed that the bacterium joins in with the spices. Hence sanitary and operating rulls for raw materials and the environment can not be ignored.(4)18kinds of natural products were used to study the inhibitory effect upon the three SSOs, and then the best composites of biological antibacterial agents were optimized. The results showed that:First, Garlic, cinnamon, nutmeg, and tea polyphenols had good antibacterial effect on SSOs. According to Orthogonal t value method by using these four natural products extracts, the optimal composite biological antibacterial agents was acquired: Garlic extract and tea polyphenols mixed in1:1, and the minimum inhibitory concentration of the biological antibacterial agents against Lactobacillus sakei was0.56mg/mL.Second, the biological antibacterial agent complex can significantly reduce the number of microorganisms, inhibit the rate of fat oxidation and protein degradation, and the shelf life of vacuum-packed Zhenjiang Yao meat was effectively extend.(5) To understand the antibacterial mechanism of the biological antibacterial agent compounds, the impact of integrity of the bacterial cell membrane and cell wall, the protein synthesis, fatty acids composed and organic acid metabolism were studied. The results showed that:First, the biological antibacterial agent complex can damage the cell ultra structure and cell membrane integrity, can increase the permeability and reduce the mobility of cell membranes, and change the metabolism of organic acids in the cells of three SSOs. Second, there were some different in antibacterial mechanism of the biological antibacterial agent complex on different SSOs. The biological antibacterial agent complex had no significant effect on the intracellular protein synthesis of Yersinia intermedia and Lactobacillus sakei, but can significantly affect the synthesis of some intracellular key structural or functional proteins of Enterococcu faeciums. It can destroy the integrity of cell wall of Yersinia intermedia and Lactobacillus sakei, and cause the cell wall membrane separation. For Enterococcu faeciums it mainly affect the biosynthesis of the cell wall appendage and then affect its physiological activity. |
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