Modelling the combined effect of temperature and pH on the rate coefficient for bacterial growth.

An extension of a model of Davey (1989a) has been used to model data of Adams et al. (1991) describing the combined effect of temperature and pH on the rate coefficient for growth of Yersinia enterocolitica in liquid media acidified with four different acidulants: sulphuric, citric, lactic and acetic acids. The model explained between 97.8% and 99.1% of the variance in the results. This very good fit between the predictions and the observed data confirms pH can be incorporated into a model that had previously been applied to the combined effect of temperature and water activity, and to the effect of temperature alone. These findings, taken together with previously reported results, demonstrate the value of the model for predicting the combined effect of two environmental factors on the growth rate. Based on results reported in this paper and previously reported results, a generalised model is proposed for the combined effect of three or more environmental factors, that is amenable to testing.