DEVELOPMENT OF A DYNAMIC MODEL TO PREDICT THE FATE OF PATHOGENIC ESCHERICHIA COLI IN DICED CUCUMBER UNDER CHANGING TEMPERATURES

Abstract

Escherichia coli has been detected in a variety of foods, particularly in salad vegetables, such as diced cucumbers. However, it is difficult to control this pathogen in salad vegetables, because they are consumed without additional preparation or cooking. Thus, the objective of this study was to develop dynamic models to describe the kinetic behavior of E. coli in diced cucumber. The diced cucumber was inoculated with E. coli, and stored at 10 degrees C, 20 degrees C, 25 degrees C, and 30 degrees C; cells counts were then performed using Petrifilm (TM) plates. The Baranyi model was used to calculate lag phase duration (LPD; h) and maximum specific growth rate (mu(max) log CFU/g /h). These parameters were then fitted to a polynomial model, as a function of temperature, and a subsequent dynamic model was developed in accordance with these primary and secondary models. The performance of the model was evaluated by comparing predicted data with observed data to calculate the root mean square error (RMSE). As temperature increased, LPD decreased, but mu(max) increased. The secondary model effectively described the temperature effect on LPD and mu(max), where R-2 equaled 0.972-0.983. In the validation stage, RMSE value of 0.272 suggested that model performance was appropriate to predict cell counts in diced cucumber, and these predictions remained appropriate under changing temperatures. These results indicate that E. coli can grow rapidly in diced cucumber at high storage temperatures, and present a useful dynamic model for describing the kinetic behavior of E. coli in this vegetable.