Interactive Effects of Spore Load and Temperature on Aflatoxin Production ¹

The relationship between initial spore load of an aflatoxigenic mold and subsequent growth and aflatoxin production were studied at 28 and 35°C. The initial spore loads ranges <10¹ to 10⁷ spores/ml. As the spore level increased, visible growth appeared sooner and was more extensive. Growth, determined by viable plate counts, indicated that maximum growth in all the treatments reached 10⁹ CFU/g, irrespective of the initial spore load. Mycelial growth and sporulation occurred faster at 35°C at all spore levels than at 28°C. At 28°C, unusually high amounts of aflatoxin B_l (380 ug/g) were produced when 10³ spores were inoculated into 50 g rice, while the lower and the higher spore levels produced comparatively lower levels of aflatoxin. At 35°C the lowest spore level (<10¹ spores) produced the highest amount of aflatoxin B₁ (62 μg/g). The higher spore levels at 35°C either did not result in any aflatoxin formation, or the amounts produced were negligible. At 35°C many fluorescing compounds other than aflatoxins were detected.