Evaluating And Unify Models Of The Shelf Life Of Flesh And Prepared Chicken

Chicken products including fresh chicken and prepared chicken are more popularthan beast by virtue of their higher protein content and lower fat content. While freshchicken has got the majority market in terms of consumption of meat products,popularity of prepared chicken products increases due to their convenience, richnutrition and high added-value. Sichuan-style chicken skewers and chicken flesh andbones are two typical chicken products. Microorganism contamination causes shortshelf life and it is the main bottle neck of the development of chicken products.Besides, temperature is one vital external factor. In recent years, with application ofpredictive microbiology models, the shelf life and quality of chilled pork can beevaluated much more quickly compared with traditional methods. In addition, since"one breed one model" restricts the model application in the food, it is necessary toanalyze the dynamic growth parameters by study of the growth and patterns of themicroorganisms in different chicken products, and thus to realize the "unification" ofshelf life prediction of different chicken products.In the present study, the naturally contaminated chicken obtained from the plantA was used as the subject. The spoilage limit of Pseudomonas spp in the flesh chickenand prepared chicken with pallet packaging was determined by the number ofPseudomonas, TVBN value and sensory evaluation indicators. The growth law ofPseudomonas in fresh chicken and prepared chicken was examined at5,10,15,20and25°C respectively. Modified Baranyi, Gompertz and Huang models were used tofit the growth data of Pseudomonas; RSS, MSE, AIC and psedu-R2were used tocomprehensively evaluate the applicability of the three models, and decide whichmodel is most suitable to fit the growth data of Pseudomonas and to predict theshelf-life of chicken products. In addition, we determined main index of the fourindicators by PCA (principal component analysis).Square root model was validated and used to describe the relationship between temperature and growth rate, also to predict shelf life. The kinetic parameters ofpseudomonas in Sichuan-style chicken skewers and chicken flesh and bones wereanalyzed, based on which, linear regression model and the shelf life model of fleshand bones were established.The results showed that:(1) The nonlinear regression procedure of SAS9.2statistical software was usedto fit the experimental data of Pseudomonas with three models at differenttemperatures. The three models were suitable to describe the growth of Pseudomonasat5-25°C.(2) By comparing the statistical criteria RSS, AIC RSE and psedu-R2of thethree models, the results revealed that the three models gave a different goodness offit over all the data obtained at selected temperatures for different chicken products.The residual sum of squares (RSS) was determined as the most important evaluationindex by PCA (principal component analysis). The growth rate and lag phase fitted byGompertz model were determined to established secondary model of pseudomonas infresh chicken, and Baranyi model were determined to established secondary model ofpseudomonas in prepared chicken.(3) Validation of built model was carried out at10℃and12℃with the freshchicken and prepared chicken obtained from the plant A. Bias and accuracy factorsand intuitive comparison chart suggested that the development models could wellpredict the growth of Pseudomonas in different chicken products at constanttemperature.(4) With the dynamics parameters divided from primary model of pseudomonas,the “unification" regression model of growth rate and lag phase of pseudomonas inprepared chicken was built. By analyzed the otherness and similarity of pseudomonasin different products, the growth rate of pseudomonas in fresh chicken was greaterthan that of pseudomonas in Sichuan-style chicken skewers and chicken flesh andbones. However, the lag phase of pseudomonas in Sichuan-style chicken skewers andchicken flesh and bones were less than in the fresh chicken. The growth rate and lagphase of pseudomonas in the two prepared chicken meat showed the same law;therefore the “unification" regression model of growth rate and lag phase ofpseudomonas in prepared chicken was verified at5℃, where the deviation degree iswithin the scope of the accuracy, and accuracy is high.(5)With comprehensive evaluation of the number of Pseudomonas, TVBN value and sensory indictors, the spoilage limits of Pseudomonas spp. in pallet-packagingfresh chicken, prepared Sichuan-style chicken skewers and chicken flesh and bonesskewers are5.3945log(cfu/g),5.599log(cfu/g) and6.0897log(cfu/g) respectively.The present study provides equations to predict the shelf life of pallet-packaging freshchicken and prepared chicken provided that the initial number of Pseudomonasorganisms (N0) and the actual temperature are known; also provides the equationsrelating between dynamics parameters of the growth rate and lag phase; throughtransformation or adjustment, we could predict chicken flesh and bones shelf life bySichuan-style chicken skewers of the pseudomonas parameters.