Growth Models And Risk Assessment Of Staphylococcus Aureus In Raw Milk

S. aureus is a common widespread foodborne pathogen in various foods including milk and dairy products. Numerous S. aureus food poisoning incidents occurred every year, which have become a worldwide health problem. This pathogen can cause illness by the production of heat-stable enterotoxins. In this research, growth models of S. aureus under constant and variable temperatures in raw milk were established, the influence of environmental factors on production probability of enterotoxin was studied, and a quantitative risk assessment was constructed to determine the risk from S. aureus and its toxin in milk in China. The main research results were presented as follows:1. S. aureus growth in milk at10,15,20,25,30,37℃were determined, the growth data was used to establish model one. Combined with the data records of S. aureus growth in ComBase, model two was established. The internal validation results showed that the models were good to predict the growth of S. aureus in milk. External validation demonstrated that model two had a better statistic fitness than model one.2. According to the theory of "equivalent growth time", the growth models of S. aureus in raw milk under variable temperatures was established. The validation results showed that R2, Af, Bf were all close to1, indicating that predictive models were able to predict growth conditions of S. aureus in raw milk under fluctuating temperatures. In addition, the predictive models were compared with models built by Combase predictor(CP models). Results showed that in CP models, the growth rates of S.aureus were significantly greater than those in models based on milk, so prediction software should be validated when applied to specific foods.3. Established a probability Logistic model of S. aureus enterotoxin production under different temperature, pH and aw. The results showed that the concordant value was96.8%, and concordant index was0.972, indicating that the model can predict the probability of enterotoxin production in TSB both reliably. In addition, compared the predict values with the observed values in milk, model predictions were in good agreement with the observed values.4. A quantitative risk assessment to determine the food poisoning risk from the consumption of milk in China that might be contaminated by S. aureus was conducted. The results of the Monte Carlo simulation model indicated that the expected probability of milk with the contamination levels at the time of consumption greater than105CFU/mL was0. Sensitivity analysis showed that except the microorganism’s characterization, storage temperature and time on farm, treatment temperature and time at the dairy processing plant and storage time and temperature in family were the important factors affecting the contamination level at the point of consumption. To minimize the risk of milk-borne staphylococcal intoxication in China, the control of these factors is the most important step.