Shelf Life Predictive Model Of Vacuum-packaged Raw Beef

With the development of the living standard of the people,the consumption demand for the raw beef has also been increasing.Even the modern slaughter and division way can not avoid the microorganism pollution.Moreover during the following processing,storage and transport,secondary pollution can easily occur which may result to meat spoilage.What's more any additives have been forbidden in raw meat according the national standard.In addition,the shelf life of raw meat is the focus of the company's attention.So,packaging has been considered as one of the effective solution.Vacuum-package is widely used in factory.Though the vacuum-package can limit the growth of bacteria to a degree,the spoilage bacteria may multiply rapidly if the temperature of the environment changed which can also affect the shelf life.For another reason,predictive mathematical models can avoid the time-consuming and lagging of the traditional microbial enumeration techniques and also can improve the inspect level of the company.So,the paper studied the correlations between spoilage parameters and the main spoilage microorganisms of vacuum-packaged refrigerated raw beef to determine the SSO of the vacuum-packaged raw beef.Then,comparing the fit result of the different growth models to obtain the best fitted model,and verified it.The shelf life model of the vacuum-packaged raw beef was built on the best growth model.This research is a part of the item "scientific and technological projects of national public sectors of China"(200903012).The specific research contents and results are as follows:1)Study on the dominant bacteria of the vacuum-packaged raw beef usingPCR-DGGEThe dominant bacteria of the vacuum-packaged raw beef stored at 7? was studied using PCR-DGGE,the result revealed DGGE bands were few and not bright enough during the early period,indicating the diversity during this period is low.The diversity of the bacteria was stable and the bands were richer with the storage time prolonged.Well during the last period,the diversity was reduced except the dominant bacteria and the seudomonas spp.and the Lactic acid bacteria were the dominant bacteria during the storage time.2)Correlations between parameters of spoilage and main spoilage bacteria of vacuum-packaged raw beefThe correlations between the main organisms and the spoilage qualities were studied.The result showed that lactic acid bacteria,Pseudomonas spp.and B.thermosphacta had remarkable relationship(P<0.01)with the spoilage qualities.The person correlation coefficients of Lactic acid bacteria with the two parameters were 0.984 and 0.881 respectively,for the Pseudomonas spp.were 0.973 and 0.908 as well as the B.thermosphacta were 0.909 and 0.890.So Lactic acid bacteria,Pseudomonas spp.and B.thermosphacta show a closely relationship with the spoilage quality of the vacuum-packaged refrigerated beef.3)Determination of the SSOs and minimum bacteria amount of spoilageCombined with the correlation of the spoilage bacteria and the spoilage qualities as well as the result of the PCR-DGGE,Lactic acid bacteria and Pseudomonas spp.were the SSO of the vacuum-packaged raw beef,and the minimum bacteria amount of spoilage were 6.37 1g(cfu/g)and 7.12 Ig(cfu/g)respectively.4)Building and verifying the growth models for SSOsFour growth models-Baranyi,Logistic,modified Gompertz and Huang models were fit with the Lactic acid bacteria and Pseudomonas spp.of the naturally pullulated vacuum-packaged raw beef at 5,7,10,15,20 and 25 ?.MSE,AIC and Pseudo-R2 were selected as the statistical criteria,and the square root model was selected to describe the relationship of the temperature with the ?max1/2 and 1/?1/2.The result showed that all of the four models can fit the data of the Lactic acid bactria and Pseudomonas spp.well,and no obvious differences were discovered.No obvious liner relationship was showed between the temperature and the 1/?1/2 of the Pseudomonas spp.,which was weaker than that of the Lactic acid bacteria.The fit of the square root model with the ?max1/2 and 1/?1/2 obtained from the modified Gompertz model were better.5)The predictive model of the shelf life of the vacuum-packaged raw beefSquare root model could not describe the relationship of the temperature and the growth dynamical parameters of Pseudmonas spp.well,and the good fitting result of the first and secondary model of Lactic acid bacteria,the predictive model of the shelf life of the vacuum-packaged raw beef were based on the Lactic acid bacteria,the equation was:SL=?-[(7.1469-N0)/?mxa×2.718]*ln{-ln[(6.37-N0)/(7.1469-N0)]-1},the remaining shelf life can be predicted as well as the N0 and T were determined.