Predicting fungal growth: the effect of water activity on Penicillium roqueforti.

The effect of water activity on the colony growth of Penicillium roqueforti is studied by predictive modelling techniques. Measured colony diameter growth curves are fitted to estimate the growth rate and lag phase of the curves. The colony growth rate was modelled by a quadratic function of transformed water activity (a(w)) values, as suggested by Baranyi et al. (Food Microbiol. 10 (1993) 43-59). The lag time was modelled as a function of water activity, by means of the sum of a constant term and a hyperboloid function of a(w) raised to the second power. The lag-phase of Penicillium roqueforti was found insensitive to the water activity in the range of its higher (a(w) > 0.92) values.