The Shelf Life Predictive Model Of Chilled Pork

The chilled pork was popular with consumers because it is full of nutrition and its good taste. However, the environment temperature during the production, storage and transportation fluctuates from time to time. It makes it’s higher to the temperature 0~4℃, and affect the safety and shelf life of product.The traditional microbiology analysis takes a long time for 48 hours for us to know the result though it is accurate. It can not predict the changes and can not be applied to the temperature and quality control of chilled pork in the product chain.The predictive microbiology is an effective method to enhance the level of product safety supervisory, which could be applied to evaluate the shelf life of chilled pork by predictive model.This research is a part of project funded by Shanghai Science Commission 2007(07dz19508). The main research content is to analyze the microorganisms and the quality of chilled pork, which will change during storage of time, to develop the predictive model for shelf life prediction of chilled pork.The main research is as follows:1. The isolation and identification of pseudomonas spp. from chilled pork 6 Pseudomonas strains were isolated from chilled pork, and which of them were pseudomonas putida P1 and P2, pseudomonas fluorescens P3 and P4 and pseudomonas fragi P5 and P6.2. The growth predictive model of pseudomonas putida P1 under pure culture conditions. The secondary model which fomula is U = 0.01745(T + 8.7335) was developed under pure culture experiment through microbiological counts under storage experiment under different temperatures. The effect of predictive model developed by pure culture is evaluated by bias factor and accuracy factor, which were 3.4 in this research, and failed to predict the growth of pseudomonas spp.of chilled pork. 3. The predictive model of pseudomonas spp. (the mixture of pseudomonas P1,P2,P3,P4,P5,P6)under pure culture conditions.The research is to develop a predictive model on the mixture of 6 pseudomonas strains isolated from chilled pork. The secondary model is lnU=36.579-(91.422/0.008314T) , which was applied to predict the growth of pseudomonas spp. of chilled pork. The bias factor and accuracy factor of it were 1.225 and 1.227,the effect of this predictive model is not so good.4. The shelf life prediction and quality variation of chilled porkBy analyzing different physical and chemical analysis of chilled pork under plastic wrap at the 4、7、10、15℃under aerobic storage conditions, the results is as follows: the freshness of chilled pork could be evaluated by the pH of homogenate of chilled pork when the temperature varied from 7℃to 15℃. The TVBN and TBARS value increased with the storage time and temperature. The L* and b* value were related to the sensory evaluation. The lightness of chilled pork would weaken significantly, and the b* value increased during the storage.This research was to establish the predictive model of chilled pork stored at 4~15℃under aerobic conditions. The primary model was the modified Gompertz, modified logistic and Baranyi model.The square root model and Arrhenius model were applied as the secondary model. According to the predictive model based on the total aerobic counts of chilled pork,the shelf life of chilled pork was the time needed for the total aerobic microbe to proliferate from initial counts(No) to minimum counts(Ns)The shelf life model of chilled pork stored under 4~15℃was (?)This model was applied to predict the shelf life of predictive value and observed value of shelf life of chilled pork. The result showed the relative error was 12.17%, which could be applied to predict the shelf life of chilled pork under 4~15°C with high precision.5. The freshness and shelf life analysis of chilled pork by electronic nose.The electronic nose was applied to analyze the changes of freshness and shelf life of chilled pork. Under the experimental temperature: 4°C,7°C, 10°C, 15°C, 4°C/12h~7°C/12h and 4°C/12h~10°C/6h~15°C/h. The result from electronic nose was similar to the sensory evaluation. The average relative error of electronic nose when it was applied to predict the shelf life of chilled pork under 4 isothermal temperature is 6.97%. And the good liner relation was found between the response value of electronic nose and sensory scores.The PLS analysis method was applied to analyze the relevance between the microbe counts and response of electronic nose under 4°C,7°C, 10°C, 15°C, 4°C/12h~7°C/12h and 4°C/12h~10°C/6h~15°C/h. The relative coefficient of which were 0.9784,0.9847,0.9983,0.9931,0.9830 and 0.9931.The relative coefficient between sensory scores and response of electronic nose were 0.9910,0.9708,0.9852,0.9936,0.9756 and 0.9925.The shelf life prediction of chilled pork stored under 4°C,7°C, 10°C, 15°C, 4°C/12h~7°C/12h and 4°C/12h~10°C/6h~15°C/h by electronic nose were 4.5,4.0,3.5,1.2,4.7,3.8 days respectively. The relative error of sensory evaluation and observed data were 6.25%,2.56%,9.37%,9.09%,6% and 8.57%.The electronic nose could be applied to predictive the shelf life of chilled pork quickly when the temperature varied from 4 to 15℃.