A temperature-type model for describing the relationship between fungal growth and water activity

Growth of Penicillium chrysogenum, Aspergillus flavus, Cladosporium cladosp orioides and Alternaria alternata at their respective optimum temperatures was studied in Potato Dextrose Agar (PDA) medium at different water activit ies (a,) adjusted with glycerol. The growth rate( CL) was expressed as the increase in colony radius per unit of time. This paper extends the model th at showed the relationship between temperature and bacterial growth rate de veloped by Rosso et al. [J. Theor. Biol. 162(1993) 447] to describe the inf luence of a, on fungal development. An excellent correlation between the ex perimental data and the model predictions was obtained, the regression coef ficients (r(2)) were greater than 0.990, with the exception of that for A. flavus (r(2) = 0.982). In addition, the use of such a model allows predicti ons of the cardinal water activities: a(wmin), a(wopt), and a(wmax),. The e stimation of the minimum water activity (a(wmin)) was in accordance with da ta literature for all the moulds considered here, hut seemed to be slightly underestimated for P. chrysogenum and A. flavus when compared to our exper imental values. The estimations of the optimal water activity (a(wopt)) and the optimal growth rate (mu (opt)) were in excellent agreement to the expe rimental results for the four moulds. Through this example, it is suggested that the same approach for modelling can be used for various microorganism s (e.g. bacteria and moulds), and different environmental parameters (e.g. temperature and water activity). (C) 2001 Elsevier Science B.V. All rights reserved.