Growth and aflatoxin production of an Italian strain of Aspergillus flavus: influence of ecological factors and nutritional substrates

The aim of this study was to define quantitative relationships between temperature and water activity (aw), fungal growth and aflatoxin B1 (AFB1) production. A strain of A. flavus isolated from maize in North Italy, and previously tested and found positive for AFB1 production, was used for these experiments. The optimum temperature for AFB1 production was at 25°C, slightly lower with respect to results obtained in other countries. 0.83 aw was the limit for growth of this strain of A. flavus after 60 days incubation at the optimum temperature. The solutes used to modify aw, glycerol and NaCl, influenced both growth and secondary metabolite production. Media modified with glycerol resulted in more AFB1 production when compared to the non-ionic solute NaCl added media. Maize based media, prepared with flour obtained from kernels at different ripening stages, only slightly influenced growth rates of A. flavus. The quantitative relationship obtained between fungal growth and AFB1 production in diverse temperature and aw levels were used to develop a valid predictive model for A. flavus presence and AFB1 production in the field