Risk Assessment Of Escherichia Coli And Staphylococcus Aureus In Frozen Fresh Shelled Shrimp And Product Shelf-life Prediction

Our country is rich in variety of shrimps including sea shrimps, brackish water shrimps and freshwater shrimps because of the broad sea area of our country. Penaeus vannamei is one outstanding representative of brackish water shrimp for its thin shell, fresh texture and easy cultivation. And the frozen fresh shrimp products processed by Penaeus vannamei are very popular in the domestic and international markets and have become one of the major export aquatic products. However, due to the lack of research into the risk assessment of frozen fresh shrimps, some developed countries establish rigorous trade technical barriers nearly one decade, which include limit value of many types of pathogenic microorganisms. Escherichia coli and Staphylococcus aureus are common pathogenic microorganisms that frequently cause food poisoning events which show increasing trend year by year.The production of frozen fresh shrimps are made of many procedures including raw shrimp farming, transportation, storage, further processing carried out in factory, etc. If technological rules or supervisions are not strictly implemented in one procedure, it will probably cause increasing bacterial outbreaks that finally lead to excessive pathogens and may increase the risk of consumptions of frozen fresh shrimps.The content of this research and findings are as follows:1. By taking the shrimp farm as the experiment base and tracing determinations of the growth of Escherichia coli and Staphylococcus aureus in both pool water and shrimps, primary models of the two pathogens in pool water and shrimps are established. Models which reflect the relationships between the growth of pathogens in pool water and in shrimps are also made, enabling grasping the change of the two pathogens after their contaminations to farming environment.2. Primary models of Escherichia coli and Staphylococcus aureus at different temperatures which reflect different producing processes in factory are established. By comparing the growth rate of pathogen counts, critical controlling procedures during processing are confirmed. Growth rate square-root secondary models are also set up and model validations are carried out. Secondary models show the minimum growth temperature of E.coli is 3.90℃, while Staphylococcus aureus is 2.80℃.3. Primary growth models of total bacterial count in shrimps at different temperatures are built, which are the base of the establishment of growth rate secondary square-root model and lag time secondary square-root model. Validations of the two models are carried out. The product shelf-life prediction indicates that the shelf-life predictive value of frozen fresh shrimp product at 4℃is 81.23 h, which is consistent with the actual observation.4. Predictions of the count changes of E.coli and Staphylococcus aureus in the production flow consist of farming, transportation, processing, marketing and eating are made, by adopting already known models and combining with some assumptions and survey data. Morbidity caused by eating frozen fresh shrimps is predicted by application of Monte Carlo method, in which random probability distribution models are made.5. According to the risk status of E.coli and Staphylococcus aureus during processing, the corresponding risk management measures were put forward in order to provide references for manufacturers and relevant supervisory authorities as well as to control the risk of the two kinds of pathogen in frozen fresh shrimps and extent the product shelf-life effectively.