Mathematical Modeling Of Salmonella In Raw Oyster And Kinetics Studying Of Ozone Sterilization

Oyster is a kind of precious seafood using as both medicine and food.But the oysters are often infected by bacteria,especially Salmonella,in growth,capture,transportation and marketing.The large number of Salmonella accumulated in oysters can threaten life safety of consumers.To solve the problem that the raw oysters caused Salmonella poisoning incidents and estimate and control the survival condition of the microorganisms in raw oysters effectively and then found a safe and effective sterilization method,this task studied the growth of Salmonella in raw oysters using microbial predictive model and developed primary and secondary models to describe the growth of Salmonella and meanwhile the raw oysters were sterilized using ozone water and then developed kinetics equation of ozone sterilization.1.Firstly,the rifampicin resistant strains of Salmonella were obtained and the result showed that the growth rates of the resistant strains were not changed and the resistant strains of Salmonella could be used to inoculate oysters in this study.Studying the growth of the microorganisms in raw oysters after Salmonella strains were inoculated,the result showed that the growth of Salmonella in oyster was nearly stable at 4?.Therefore,Salmonella could grow in oyster under 8? to 43 ?condition,and the growth of Salmonella at 4? could not fitted with primary model.The growth curves of Salmonella were sigmoidal and the growth rates increased gradually with the temperature growing.Under all selected temperatures,the initial concentration of Salmonella,background microorganisms and total microorganisms in oysters were consistent and the mean initial concentration of Salmonella,background microorganisms and total microorganisms were respectively 2.73 log CFU/g,4.48 log CFU/g and 4.54 log CFU/g.And all the maximum bacterial populations of Salmonella,background microorganisms and total microorganisms were consistent for all selected temperatures and the mean maximum bacterial concentration of Salmonella,background microorganisms and total microorganisms were 6.83 log CFU/g,7.7 log CFU/g and 7.77 log CFU/g,respectively.2.Secondly,each individual growth curve under selected temperatures was fitted to all four primary models,Huang model,Baranyi model,Re-paramenterized Gompertz model and Three-Phase Linear model.The result showed that Huang model was particularly suitable for describing the growth of Salmonella in oyster than Baranyi model,Re-paramenterized Gompertz model and Three-Phase Linear model.The population of Salmonella increased little at the beginning and then grow rapidly at exponential phases and ultimately the population were constant at stationary phases.And the lag phase became short with the temperature increased.As for background microorganisms,Huang model also could be used as the primary model of background microorganisms.The population of background microorganisms increased little at the beginning and then grow rapidly at exponential phases and ultimately the population were constant at stationary phases.And the lag phase of background microorganisms became short with the temperature increased.3.Thirdly,the data of the specific growth rates of Salmonella at all temperatures were fitted to four secondary models,Ratkowsky square-root model,Huang square-root model,Cardinal model and Arrhenius-type model.The result showed that the secondary model of Salmonella in oyster was Huang square-root model and the estimated minimum and maximum temperatures of the growth of Salmonella were 5 ? and 48 ?,respectively.And the secondary model of background microorganisms in oyster was Ratkowsky square-root model and the estimated minimum and maximum temperatures of the growth of background microorganisms were 2.8 ? and 52?,respectively.The establishment of predictive models can be used to set critical limits and conduct risk assessment for raw oyster to prevent or reduce potential risk of Salmonella growth in raw oyster.The utility of these models can help regulatory agencies and food retailers to develop safe storage temperatures for raw oyster and predict the microbial shelf-life of raw oyster.4.Finally,the single factor method and central composite rotatable design of ozone sterilization to Salmonella in oyster were studied.With the process optimizing of ozone sterilization by central composite rotatable design,the mathematical model of the reduced number of Salmonella(y)with the ratio of oyster to ozone water(x1),the concentration of ozone water(x2)and the operating time(x3)is:y =-1.58517+0.96815x1+1.42274x2 +0.40978x3-6.25×10-3x1x2+1.5625 ×10-3x1,x3+0.02875x2x3-0.073055x,2-0.38399x22-0.025767x32The best parameters of ozone sterilization obtained from this model were:the ratio of oyster to ozone water was 1:6.63,the concentration of ozone water was 2.15 mg/L and the operating time was 9.35 min.The repeated test under this condition showed that the reduced number of Salmonella was 5.08 log cfu/g.The effect of the ratio of oyster to ozone water and the operating time to sterilization both were very significant,and the effect of the concentration of ozone water was significant.The interaction of all the factors were not significant.