Effect of Temperature on Mycelia Growth and Aflatoxin B1 Production of Aspergillus flavus and Aspergillus parasiticus on Niger Seeds

Introduction: Aflatoxin (AFB₁) is produced by Aspergillus flavus and A. parasiticus, which contaminate crops before and after harvest. Consumption of AFB₁ causes both animal and human diseases including liver cancer. Niger seeds (Guizotia abyssinica) are commonly processed for cooking oil and noug cake (a byproduct from Niger seed oil factories) is commonly used in cattle feed. A previous study showed that cows fed with AFB₁ contaminated noug cake excrete aflatoxin M₁ in their milk. To prevent AFB₁ contamination in Niger seed oil and noug cake, it is critical to determine storage conditions that support growth and AFB₁ production of A. flavus and A. parasiticus in Niger seeds.

Purpose: The purpose of this study was to determine the effect of temperature on mycelia growth and AFB₁ production of A. flavus and A. parasiticus on Niger seeds after 5 and 10 days of incubation.

Methods: Individual plates containing ground Niger seeds, which were adjusted to water activity of 0.98, were inoculated with 10 μl (10⁶ spore/ml) spore suspension of A. flavus NRRL: 6513 or A. parasiticus NRRL: 2999. Plates were incubated at 20, 30, and 35°C for a total of 10 days and mycelia growth on each plate was recorded daily. AFB₁ was quantified via indirect ELISA after incubation for 5 and 10 days.

Results: Incubation temperature significantly affected both mycelial growth and AFB₁ production of the two fungi. The maximum growth rates and AFB₁ production of the two fungi were observed at 35°C after 10 days of incubation. 

Significance: The results collected from this study may be useful to establish a storage guideline for Niger seeds.