Fitting of colony diameter and ergosterol as indicators of food borne mould growth to known growth models in solid medium

Growth of a range of 14 common food spoilage fungal species was evaluated along time as a function of both colony diameter and ergosterol content on malt extract agar. Growth was assessed under different environmental conditions following a central composite design. The suitability of using either linear, Gompertz's or Baranyi's models for primary modelling of the results was tested. Regarding colony diameters, using either linear or asymptotic Baranyi's function gave better estimations of growth rate and lag phase when no asymptotic trend was observed. When a decrease in growth rate was observed with time, standard Baranyi's model was chosen, although the search for new mechanistic models specific for moulds would probably improve the estimations. The use of Gompertz equation led, in general, to overestimated parameters. Ergosterol showed good performance as a fungal growth indicator for the whole range of species. Finally, significant correlation coefficients were found between ergosterol and colony diameters, suggesting that both parameters may be useful for primary modelling and thus for subsequent secondary modelling.