| Vibrio parahaemolyticus is a natural inhabitant in estuarine marine water and seafood has been recognized as the most frequent vehicle for this pathogenic bacterium. Along with the increase of supply and consumption of seafood worldwide, the illnesses outbreaks associated with V. parahaemolyticus have aroused concerns over the public health. Various intervention methods for reducing the bacteria in seafood products have been investigated and practiced. Each method has distinct advantages and disadvantages depending on the properties of products, the conditions of processing, and the preference of consumers. The successful application of appropriate intervention strategies could effectively reduce the contamination of V. parahaemolyticus in seafood, and consequently contribute to the reduction of public health risk. The principal aim of quantitative microbial risk assessment (QMRA) is to quantify the level of risk in order to prevent unacceptable exposures and to design improved production, processing, distribution, and preparation systems that would help in reducing exposures to acceptable limits. The risk assessment process helps to identify any of those stages from production to consumption that contribute to an increased risk of foodborne illnesses. QMRA has been recognized as a predictive and decision-making tool in organizing available data, and assessing the impact resulting from exposure to different pathogens.The main contents and resultsof this study are summarized as follows.(1) Lactic acid and chitosan are natural antimicrobials for food decontamination in the washing process of seafood. In this research, a4-factor response surface model based on the Box-Behnken experimental design was developed to evaluate the effects of lactic acid (1%,2%, and3%, v/v), chitosan (0.4%,1%, and1.6%, w/v), rotational rate (90,110, and130rpm) and washing time (10,20, and30min) on reduction of V. parahaemolyticus inoculated in raw peeled shrimps. These treatments achieved2.2to4.3log10CFU/g reduction of V. parahaemolyticus in shrimps. Stepwise stratification led to a simplified model that has satisfactory performance as evidenced by statistical indices (R2=0.92; p<0.0001; RMSE=0.196) and external validation parameters [bias factor (Bf)=1.01; accuracy factor (Af)=1.05]. The model generated an optimum treatment combination (3%lactic acid,1.6%chitosan, and rotational rate at110rpm) that could achieve greatest bacterial reduction of4.5log10CFU/g. Among the four factors, lactic acid and chitosan were the major contributors for bacterial decontamination. Analysis of variances showed a significant interactive inactivation effect (p<0.05) from combined use of lactic acid and chitosan. The treatments did not have adverse effects on the quality attributes such as color and pH of the shrimps.(2) The effect of thermo-ultrsound treatment on the survival of V. parahaemolyticus in raw peeled shrimps was investigated in this study as an alternative inactivation method in seafood postharvest washing process. Raw peeled shrimps inoculated with V. parahaemolyticus were treated with mild heat (47,50, and53℃) combined with ultrasound (0.96,150, and204W) based on a3×4full factorial design and the bacterial survival curves were fitted with a Weibull model. Due to the high correlations of the shape parameter "n" and the scale parameter "n" in the Weibull model, an overall n-value was estimated from the whole set of bacterial inactivation data and n-values were estimated for each set of inactivation curve accordingly. A response surface model was generated to describe the scale parameter as a function of temperature and ultrasonic power. The results indicated that the Weibull model with the overall n-value could be used to describe the bacterial reduction with the time of exposure to the thermo-ultrasound treatments, which is well evidenced by the small values of root mean square errors (RMSE) and the high values of correlation of determination (R2). The quadratic model was validated with independent experiments within the prediction range. Statistical indices (R2=0.99; p<0.0001; RMSE=0.17) and validation parameters (Bf=0.97; Af-1.03) showed a satisfied performance of the quadratic model. The results indicated that the thermo-ultrasound treatment was effective, simple, and cost effective for inactivation of V. parahaemolyticus in shrimps during postharvest washing process.(3) Weakly acidic electrolyzed water (AEW) was used in combined with lactic aicd to reduce V. parahaemolyticus in raw peeled shrimps. A3-factor response surface model based on the Box-Behnken experimental design was developed to evaluate the antimicrobial effects of AEW (1/3,2/3and3/3, ratio, v/v), lactic acid (1%,2%, and3%, v/v), and rotational rate (90,110, and130rpm). The investigation results showed that the treatments achieved1.36～4.02log10CFU/g reduction of V. parahaemolyticus in shrimps. The developed model proved a satisfied prediction performance as evidenced by statistical indices (R2=0.99; p<0.0001; RMSEO.104) and external validation parameters (Bf=1.01; Af=1.09). The model generated an optimum treatment combination (100%AEW,3%chitosan, and rotational rate at130rpm) that could achieve greatest bacterial reduction of4.36log10CFU/g, which met the guideline value (3.52log10CFU/g) suggested by FDA for industrial invention method to remove Ⅴ. parahaemolyticus from seafood. Among the four factors, lactic acid and AEW were the major contributors for bacterial decontamination. Analysis of variances showed a significant interactive inactivation effect (p<0.05) from combined use of AEW and lactic acid.(4) In this study, a quantitative risk assessment model comprising initial bacterial contamination, post-harvest washing, transport to market, retail storage, transport to household, home storage and consumption was developed to evaluate the relative effectiveness of different post-harvest washing treatments on reducing the risk reduction by Ⅴ. parahaemolyticus in frozen peeled shrmps. Three treatments were lactic acid combined with chitosan (LA+CH), thermo-ultrasound treatment (TH+UL), and weak acid electrolyzed water combined with lactic acid (AEW+LA). Data obtained from laboratory experiment, scientific literatures, professional suggestion and assumption were used to parameterize the input variables and the growth/survival kinetics of Ⅴ. parahaemolyticus at different processing stages. The model was run using Monte Carlo simulation with100,000iterations. The simulated results showed that the risk of illness was2.5×10-9/year/person the number of illnesses per year should be344.7in China. The result of our study is reasonable as compared with the epidemiological data and results of previous risk assessment reports. Sensitivity analysis identified that the temperature and time of harvest were the most significant risk factors. Scenario analysis showed that LA+CH, TH+UL AEW+LA treatments reduced the risk of illness to2.5%,24.0%and2.6%as compared with the baseline model, respectively, suggesting the intervention method could potentially reduce the risk of Ⅴ. parahaemolyticus in frozen peeled raw shrimps. The risk model can assist seafood industry in adopting appropriate risk mitigation strategies to reduce seafood-borne illness caused by Ⅴ. parahaemolyticus. |
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