The effects of different water activities (a(w)) and temperatures on growth of storage moulds (Aspergillus candidus and Penicillium implicatum) on maize and paddy rice grains were measured using ergosterol content and dilution plating. The results showed that the mode of fungal growth depends on a(w). In all cases, conidiation occurred more readily at low a(w), whereas mycelial growth is more marked at higher a(w). The xerotolerant, thermophilic characteristics of A. candidus were more clearly revealed by the ergosterol content, which reflected mycelial development, than by enumeration of spores formed. The ergosterol content proved to be a better index of technological quality of cereals (assessed by acidity) than the number of fungal propagules. A 10-fold increase in the number of spores corresponded to a doubling of the ergosterol content.
