| Chinese spiced beef is a traditional cooked meat product and ofen sold in bulk. The shelf life of the product is short and affected the mass production of this industry. At present, although companies have started using vacuum packaging method to improve the shelf life, heat packaging or secondary sterilization is not used due to the consideration of keeping good taste. Only use cold packaging technology and poor control of sanitation and cold chain led to the current vacuum packed products easy to rotten. For vacuum packed spiced beef, this study is aimed at predicting and extending the shelf life based on the theory of predictive microbiology, which can improve the ability of middle and small companys to guarantee food safety.Firstly, sensory score, physical and chemical index and microbial index of vacuum-packed spiced beef were determined under different temperature, founding that total microbial counts had exceeded standard limits the 6th day at low temperature(4°C) and the 2nd day at room temperature(25°C). During the storage period, the sensory characteristics were gradually deteriorated with the increase of total microbial counts. Potentially harmful physical and chemical indicators, including putrescine, histamine, tyramine, TVBN, colour dfference, and exudation rate, increased as the total microbial counts rose, and there existed significant correlation. Then microflora of spiced beef at the end of storage was determined by adopting selective culture medium. It was found that microflora composition under different temperature. Separation and identification of major spoilage organisms were carried out. 16 srDNA sequencing results showed that the spoilage bacteria of spiced beef included 1 specie of pseudomonas, 1 specie of staphylococcus, 3 species of lactic acid bacteria and 2 species of bacillus, enterobacteriaceae. And in the process of storage, the rise of the total microbial counts had significant correlation with the rise of pseudomonas, staphylococcus, lactic acid bacteria and bacillus quantity. Lactic acid bacteria includes Enterococcus faecium, Lactobacillus salivarius, Weissella viridescens had the most quantity and are the specific spoilage organisms of this spiced beef product.Secondly, the growth curve of specific spoilage organisms above were studied at different temperature(4, 15, 25, 30°C) and the modified Gompertz model was the most suitable model. The maximum specific growth rate max and lag phase λ were calculated and growth kinetic models(primary model) were obtained. Then the influence of temperature on the growth kinetics were studied, founding that max and λ had a good linear relationship with growth temperature. The secondary model was established and was verified at constant and dynamic temperature respectively. The limitation of specific spoilage organisms were determined according to the linear relationship between total microbial counts and lactic acid bacteria amount and the shelf life prediction model was established as SL=λ-[(8.096-N0)/(2.718×μmax)]×{ln[- ln(4.929-N0)/(8.096-N0)]-1}. The shelf life at 4°C was calculated as 5.83 d and was 1.69 d at 25°C which were closed to actual test results.Thirdly, the antibacterial effect of four different antibacterial agents were determined, and the result was potassium sorbate < tea polyphenol < ε-polylysine < nisin. Then the influence of nisin on the secondary model was studied, the secondary model was modified by bringing in nisin concentration as a factor.Finally, optimal distribution of the concentration of antimicrobial agent was studied using the response surface method and the bacteriostatic rate as index, the result is nisin 0.0878 g/kg, ε-polylysine 0.164 g/kg and tea tree polyphenol 0.367 g/kg. Then antimicrobial agents were added into spiced beef production according to this distribution, fouding that shelf life was17 d at 4°C and 3d at 25°C. |
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