Study On Bacillus Cereus Control During Process Of Light-baked Mussels

Mussels were famous with delicious taste, rich nutrition, and high moisture content, but traditional freezing, drying, high-temperature sterilization and other processing techniques often caused damage to the flavor, nutrition, texture, color and other qualities of mussels. Processing conditions of light-baked mussels were mild to avoid the adverse effects of a few traditional high-strength treatments on the flavor and nutrition of the product, better preservation of the quality of fresh products. But it was more difficult to control the pathogens since strong sterilization during process was not used.Bacillus cereus was opportunistic pathogens, not only led to the corruption of light-baked mussels, but also caused food poisoning. Due to the diversity and complexity of microbial ecology in the process of light-baked mussels, heat-resistant Bacillus cereus would be difficultly controlled if the entire process were not controlled and hurdle factors of inhibiting its growth were quantized by establishing the growth/no growth interface model. In order to ensure the top quality and safety of light-baked mussels by setting and quantifying mild hurdle factors, the entire process of light-baked mussels was simulated in the lab, and microflora changes and the key influencing factors on which were investigated and analyzed to determine critical control points(CCP) of microbial hazard control and main pathogens. And the growth/no growth interface model was established based on related pathogen and the key influencing factors(temperature, water activity and p H) on which. Besides, its prediction accuracy and applicability were verified and evaluated. The main research was summarized as follows:(1) The process of light-baked mussels was simulated in the lab, the correlation between the process parameters(temperature and time, water content and water activity and p H) and microflora changes(bacterial abundance and bacterial flora composition) of which was analyzed combine with the changes of texture and color in order to investigate microbial control during the process. It showed light-baked mussels were process-mild products, microbial hazard control of which mattered. Total bacteria count decreased significantly during the process, but heat-resistant bacteria count decreased slightly, which indicated most of the non-heat-resistant bacteria was killed after alternating heat and cold three times. And total bacteria count of the finished product was less than 300 CFU/g, most of which were identified as Bacillus cereus. Temperature and time and water activity(or moisture content) had significant effects on the changes in total bacteria count significantly, and p H had no significant effect but the synergistic effect. Drying and baking processes and the seasoning impregnation were the key processes of water activity and moisture content control and p H control respectively, which can be determined as critical control points(CCP) of microbial hazard control. Besides, temperature and time was strictly controlled during the safe production process, especially for alternating heat and cold three times. Considering the changes of organoleptic quality(texture and color), water activity(or moisture content) and p H should be reduced, and water activity, moisture content, and p H of light-baked mussels were 0.905±0.005, 46.5%±1.3%, and 5.81±0.02.(2) The growth/no growth interface model(logistic regression model) of Bacillus cereus on light-baked mussels was established by R software based on storage temperature, water activity and p H. It showed storage temperature, water activity, p H and their interaction had significant effects on the growth/no growth of Bacillus cereus(p<0.05). And the lower storage temperature, water activity or p H, the growth of Bacillus cereus was inhibited worse. With the increase of temperature, p H or water activity, their interaction replaced the status of the individual mainly influencing the growth probability of Bacillus cereus. And one of two factors of the interaction enhanced, and the other weakened. The total equation of this model, Lopit(p)=-208.457-2.167·T+35.304·p H+705.573·Bw+1.117·T·p H-7.072·T·Bw-174.946·p H·Bw, had important guidance function for ensuring microbiological safety and the nutritional and sensory quality of the products themselves.(3) The fitting of the growth/no growth interface model of Bacillus cereus(ATCC49064 and DSMZ4312) on light-baked mussels based on storage temperature(T), water activity(Aw) and p H and the validation behavior of Bacillus cereus(YB001) from light-baked mussels were analyzed and evaluated. And this model was compared with the established growth/no growth interface model of Bacillus cereus in Brian Heart Infusion(BHI) media. It showed a reasonable goodness of fit of this model due to R2-Nagelkerke=0.979 and χ2=0.019(df=8, p=1), and the predicted concordance rate(92.19%) of this model was significantly higher than that of the established model in BHI medium, which indicated that this model had a high accuracy and good applicability in predicting the growth probability of Bacillus cereus on light-baked mussels. And the predicted concordance rate of the established model in BHI medium was 84.38%, indicated its applicability and versatility are also good, but its false negative rate was as high as 15.62%. Therefore it is more accurate to establish the growth/no growth interface model of Bacillus cereus based on light-baked mussels.