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 (a(w)), fungal growth and aflatoxin B-1 (AFB(1)) production. A strain of Aspergillus flavus isolated from maize in north Italy, and previously tested and found positive for AFB(1) production, was used for these experiments. The optimum temperature for AFB(1) production was at 25 degrees C, slightly lower with respect to results obtained in other countries. 0.83 a(w) was the limit for growth of this strain of A. flavus after 60 days incubation at the optimum temperature. The solutes used to modify a(w), glycerol and NaCl, influenced both growth and secondary metabolite production. Media modified with glycerol resulted in more AFB(1) 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 AFB(1) production in diverse temperature and a(w) levels were used to develop a valid predictive model for A. flavus presence and AFB(1) production in the field.