Mycotoxins in foodstuffs. XII. The influence of the water activity (a-w) of cakes on the growth of moulds and the formation of mycotoxins.

The influence of various a-w values (high, moderate and low, e.g. 0.92, 0.87, and 0.82) of cakes ("Rührkuchen", made of wheat flour, sugar, eggs, fat and water) on the development and the mycotoxin production of Aspergillus flavus (aflatoxins), A. versicolor (sterigmatocystin), A. ochraceus (ochratoxin A), Penicillium chrysogenum (citrinin) and P. expansum (patulin) was investigated. None of the moulds was able to germinate at an a-w of 0.82. An increase of the water activity resulted in a pronounced growth of the five fungi. Citrinin was not formed on the cakes at all. The yields of the other mycotoxins were not markedly influenced by the a-w (0.92 or 0.87). During the development of the moulds the a-w of the substrate was lowered at first (water requirement during germination and initial growth) and subsequently increased (initiation of the secondary metabolism).