Metal Ions in Activated Carbon Improve the Detection Efficiency of Aflatoxin-Producing Fungi

Aflatoxins (AF), produced by several Aspergillus species, are visible under ultraviolet light if present in high amounts. AF detection can be improved by adding activated carbon, which enhances the observation efficiency of weakly AF-producing fungi. However, commercial activated carbon products differ in their characteristics, making it necessary to investigate which characteristics affect method reproducibility. Herein, the addition of 10 activated carbon products resulted in different AF production rates in each case. The differences in the production of aflatoxin G₁ (AFG₁) were roughly correlated to the observation efficiency in the plate culture. Trace element analysis showed that the concentrations of several metal ions differed by factors of >100, and the carbons that most effectively increased AFG₁ production contained higher amounts of metal ions. Adding 5 mg L⁻¹ Fe or Mg ions increased AFG₁ production even without activated carbon. Furthermore, co-addition of both ions increased AFG₁ production stably with the addition of carbon. When varying the concentration of additives, only AFG₁ production increased in a concentration-dependent manner, while the production of all the other AFs decreased or remained unchanged. These findings suggest that a key factor influencing AF production is the concentration of several metal ions in activated carbon and that increasing AFG₁ production improves AF detectability.