A new model for germination of fungi.

The objective of this study was to design a germination model dedicated to fungi. The percentage of germinated spores, P(%), depended on the maximum percentage of germination P(max) (%), the germination time, τ (h) and a design parameter, d (-) according to : [formula in text]. The model was capable to fit satisfactorily either apparent symmetric and asymmetric shapes of germination curves. The accuracy of τ determined by using the logistic or the present model was at least twice that obtained by the Gompertz equation. In contrast to the logistic model, the new model is by essence asymmetric. Therefore, its use is consistent with skewed distributions of the individual germination times that were observed experimentally in many cases.

Impact of water activity of diverse media on spore germination of Aspergillus and Penicillium species.

The effects of water activity (a(w)) of diverse media i/ culture medium for sporogenesis, a(w sp) ii/ liquid spore suspension medium, a(w su) and iii/ medium for germination, a(w ge), on the germination time t(G) of Aspergillus carbonarius, Aspergillus flavus, Penicillium chrysogenum and Penicillium expansum were assessed according to a screening matrix at 0.95 and 0.99 a(w). It was shown that i/ reduced t(G)s were obtained at 0.95 a(w sp) except for P. expansum ii/ a significant effect of a(w su) on t(G) was demonstrated for A. carbonarius, P. chrysogenum and P. expansum iii/ the most important factor for controlling the germination time was the medium for germination except for A. carbonarius (a(w su)). In accordance with the fact that fungal spores can swell as soon as they are suspended in an aqueous solution it is recommended to re-suspend fungal spores in a solution at the same water activity as that of subsequent germination studies.

Significance of the physiological state of fungal spores.

In predictive mycology, most of the studies have been concerned with the influence of some environmental factors on fungal growth and production of mycotoxins, at steady-state. However, fluctuating conditions, interactions between organisms, and the physiological state of the organisms may also exert a profound influence on fungal responses in food and in the environment. In the laboratory, fungal spores are widely used as a biological material. They are produced under optimal conditions then, partially re-hydrated for obtaining standardized spore suspensions. In real conditions, spores are produced under suboptimal conditions and can be submitted to various stresses prior to their germination. It was illustrated how the sporulation/post-sporulation conditions, the re-hydration and the age of the spores affected greatly their physiological state and consequently their resistance to heat, inhibitors and their germinability. It was hypothesised that the observed responses to environmental factors during inactivation and germination could be correlated to the intracellular water activity of the spores.