Modelling and predicting the effect of temperature, water activity and pH on growth of Streptococcus iniae in Tilapia.

AIMS: To evaluate and model the growth of Streptococcus iniae affect by temperatures (10-45 degrees C), water activity (A(w); 0.995-0.957), and pH (5-8). METHODS AND RESULTS: Temperatures, A(w), and pH were adjusted. The behaviour of S. iniae was studied and modelled. Growth curves were fitted by using logistic, Gompertz, and Baranyi models. The maximum growth rates obtained from the primary model were then modelled as a function of temperature, A(w), and pH using the Belehradek-type models for secondary model. The optimum values for growth were found to be in the range of 35-40 degrees C, A(w) 0.995-1, and pH 6-7. The statistical characteristics of the models were validated by r(2), mean square error, bias, and accuracy factors. The results of validation indicated that Baranyi model performed the best. CONCLUSIONS: The effect of temperature, A(w)/NaCl, pH control of S. iniae in tilapia could be satisfactorily predicted under current experimental conditions, and the proposed models could serve as a tool for this purpose. SIGNIFICANCE AND IMPACT OF THE STUDY: The suggested predictive model can be used for risk assessment concerning S. iniae in tilapia.