Bacterial Phase Variation And Establishment Of Shelf Life Prediction Model For Penaeus Vannamei During Low-temperature Storage

Penaeus vannamei is loved by more and more consumers because it contains richnutrition and tastes delicious. However, Penaeus vannamei is vulnerable to spoilage,because of its large moisture content; what’s more, it is captured in higher temperatureseasonal with rapid microorganism’s growth and high enzyme activity. The method ofsensory, chemical, physical and microbial evaluation of Penaeus vannamei was usedto establish a comprehensive evaluation the quality of Penaeus vannamei duringlow-temperature storage. The experiment intended to select suitable freshnessindicators, and provide a basis for Penaeus vannamei quality rating. To clear bacterialphase change during low-temperature storage, and reveal the spoilage mechanism ofPenaeus vannamei, dominated strains from Penaeus vannamei in different storagetemperature were isolated and purified, then identified by ATB ExpressionTMreader.Study the growth of specific spoilage organisms (SSO) at different temperatures, andestablish of predict microbial growth model of a kinetic model and secondary model,so that we can predict the shelf life quickly and efficiently.1，Freezing point of Penaeus vannamei is-1.4℃, the ice temperature zone is-1.4~0℃. Sensory evaluation, total volatile base nitrogen (TVB-N), pH value, color(L*, a*, b*), texture (hardness, springiness, resilience, flexibility, gum, chewing) andtotal bacterial count of Penaeus vannamei were measured, and did factor analysis toobtain a fresh low under Penaeus vannamei comprehensive evaluation modelprovided a theoretical basis for quality evaluation. The results showed that, in cold,ice-temperature and frozen storage, the shelf life of Penaeus vannamei were3d,8dand56d. Reduce the storage temperature can effectively extend the shelf life andbetter ensure its storage quality. But in terms of cohesiveness and springiness, icetemperature was superior to frozen storage.2. In cold, ice-temperature and frozen storage, the common major qualityindicators that reflecting freshness were sensory evaluation, TVB-N, L*, a*, hardness,cohesiveness, resilience, gumminess, chewiness. In addition, sensory scores andTVB-N value displayed strong correlations with storage time, and the can beconsidered suitable indicators to determine the extent of Penaeus vannamei corruption.TVB-N content of30mg/100g can be the judge limit.3. To clear bacterial phase change during different low-temperature storage,dominated strains from Penaeus vannamei were isolated and purified, then identified.The results showed that, in the early storage phase, the dominant strains were Chryseobacterium meningosepticum (22.0%) and Pseudomona sp.(18.4%),Shewanella putrefaciens (35.1%) and Pseudomonas sp.(24.3%) were dominant strainduring the cold storage. Shewanella putrefaciens (32.0%) and Chryseobacteriummeningosepticum (27.0%) were dominant strain during ice-temperature, andAeromonas sobria (30.5%) and Photobacterium damselae were dominant strainduring frozen storage (25.0%).4. Based on sensory evaluation and behaviors analysis, Pseudomonas sp. andShewanella putrefaciens were identified as special spoilage organisms (SSO) ofPenaeus vannamei stored at0~20℃. At the end of shelf life, the average number ofPseudomonas sp. and Shewanella putrefaciens were5.990lg(CFU/g) and5.165lg(CFU/g) at temperatures0℃,4℃,15℃and20℃. The kinetics models ofPseudomonas sp. and Shewanella putrefaciens had been developed and the resultsshowed growth dynamics of these two SSO under0~20℃could be well describedby modified Gompertz model. Using experimental values stored at0℃,4℃,15℃and20℃fitted the modified Gompertz model, the result showed that, modifiedGompertz model can be well described growth dynamics of Pseudomonas sp. andShewanella putrefaciens within the temperature range from0℃to20℃. Thetemperature had not significant between the maximum number of bacteria (Nmax), thevalue was9.109±0.312lg(CFU/g) and8.845±0.231lg(CFU/g), whereas, Specificgrowth rate (μmax) and the lag time (Lag) were influenced by temperature greatly.Belehradek model were used to describe the relationship between the temperatures (T),and showed a fine linear relationship.Validation of built kinetic models was preferred by comparing with experimentaldevelopment of Pseudomonas sp. and Shewanella putrefaciens grown on Penaeusvannamei at temperatures7℃and10℃. Bias and accuracy factors of Pseudomonassp. range from0.998to1.004and from1.102to1.177; Bias and accuracy factors ofShewanella putrefaciens range from1.006to1.010and1.058to1.194. At7℃and10℃, Pseudomonas sp. The relative error of predicted values and the real shelf life were3.16%and-4.35%; Shewanella putrefaciens established shelf life model were-2.44%and-7.29%. In conclusion, the microbial growth model built in this research can rapidand realistic predict of the microbial growth dynamics and remaining shelf life ofPenaeus vannamei during the storage within0℃to20℃.