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

Tadahiro Suzuki,Masatoshi Toyoda

doi:10.3390/toxins11030140

Abstract

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.

Highlights

Aflatoxins (AFs), which are strong carcinogens, are secondary metabolites originating fromAspergillus fungi that can be present as contaminants in animal feed and various food products [1,2].Each country has established reference values and strict controls for AFs in food processing and distribution to avoid contamination [2]
We found that aflatoxin G1 (AFG1) production by A. bombycis MAFF111712 increased upon the addition of Fe, and AFG1 production by A. nomius MAFF111739 increased upon the addition of Mg (Table 8)
When we investigated the relationship between the AF volumes in the liquid culture study and the fluorescence intensities in the plate culture study, we found that only AFG1 production corresponded to the fluorescence intensities observed in the preliminary plate test (Tables 2 and 5)

Summary

Introduction

Aflatoxins (AFs), which are strong carcinogens, are secondary metabolites originating fromAspergillus fungi that can be present as contaminants in animal feed and various food products [1,2].Each country has established reference values and strict controls for AFs in food processing and distribution to avoid contamination [2]. Climate change has led to the expansion of the distribution of AF-producing fungi from tropical to other regions, but the full extent of their distribution is unclear [3]. In the AF synthesis gene cluster, which contains the target region for the detection of AF-producing fungi, homologous or non-homologous recombination events occur throughout [5] and complicate detection. Other analyses such as ELISA, TLC, HPLC, and LC-MS are required to confirm the presence of Toxins 2019, 11, 140; doi:10.3390/toxins11030140 www.mdpi.com/journal/toxins

Methods

Discussion

Conclusion