| The environmental temperature, initial microbial contamination level and subsequent microbial growth and reproduction are important factors that affect the shelf life of meat products. To control food spoilage, it is necessary to understand the growth and reproduction patterns of the microorganisms that cause it and predict their growth at different temperatures. Microbiological predictions can do this quickly and effectively. Determining the product's specific spoilage organism (SSO/ESO) by using appropriate media for microbial growth and selecting effective mathematical equations are the foundation for a good microbiological prediction model. Therefore using naturally contaminated meat in such studies can better reflect the growth of organisms and their relationship to spoilage. In the present study, we examined the correlation between Pseudomonas and several indicators of spoilage during the storage of chilled beef and confirmed that Pseudomonas spp. are the SSO. We observed the growth of Pseudomonas spp. at 0,4,7,10,15 and 20℃in naturally contaminated chilled beef, fitted the results with the Baranyi and Roberts equation and Modified Gompertz equation and established a model to predict the remaining shelf life. Our results will provide effective risk assessment tools and methods to accurately predict the remaining shelf life of beef. In addition, in order to explore the species diversity of pseudomonas, we made pseudomonas species isolation and identification combining molecular biology and physiology and biochemistry methods, and want to master their growth law.The results showed that:1)The correlation between the growth of Pseudomonas spp. and the total number of bacteria, TVBN value, color scale L value, sensory evaluation and other quality indicators is statistically significant (P<0.01); therefore, Pseudomonas.spp are considered to be the SSO for chilled beef. It is feasible to use a Pseudomonas growth model to predict the extent of spoilage of chilled beef under aerobic storage conditions. Cluster analysis and the observations of the aforementioned quality indicators determined that the spoilage limit of Pseudomonas spp. in chilled beef is 10820 cfu/g.2)SAS statistical soft ware was used to analyze Pseudomonas. spp growth at different temperatures. The Baranyi and Roberts equation and Modified Gompertz equation were good predictors of Pseudomonas spp. growth in the beef; the growth curve were typical S-type, and the P values were less than 0.0001, MSE values were less than 0.3 and R2 values were greater than 0.95. The square root model was used to consider the maximum specific growth rate and lag phase of Pseudomonas and temperature (μmax1/2-t/λ1/2-t), and the secondary model of Pseudomonas spp. growth were obtained:μmax1/2= 0.15604[t+(-0.08472)] andλ-1/2= 0.0649+0.0242t-(P<0.01, R2= 0.936).After fitting the second model, it showed that the Baranyi and Roberts equation are better than Modified Gompertz equation.3)By comparing the residuals of ob served values with those of the predicted values, the absolute values were less than 0.05, indicating that the square root model can accurately describe the effect of different temperatures on microbial growth. We obtained chilled beef samples from several slaughter plants, and we counted the number of Pseudomonas organisms at 4 and 10℃to verify our model. The predicted values fluctuated in a range of about 10%, and the differences between predicted and observed values (Af) were less than 20%. The established secondary model using the Baranyi and Roberts equation predicted the growth of Pseudomonas in chilled beef, and it is a good foundation for further study on the suitability of this prediction model at fluctuating temperatures and to develop software to carry out these models.4)This study provides an equation to predict the shelf life of chilled beef provided that the initial number of Pseudomonas organisms (No) and the actual temperature are known.5)There were three stains isolated:P. fragi, P. putida and P. fluorescens from the chilled beef stored at 4℃aerobically. And the proportion of non-fluorescent and fluorescent pseudomonas.spp changed significantly during the storage.
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