Aflatoxins are a group of secondary metabolites produced by some Aspergillus species, including A. flavus and A. parasiticus, and are detected in many kinds of food such as corn, tree nuts, dried fruit, and spices. Because they are potent mutagens and are liver carcinogens in humans and a wide range of animal species, aflatoxin contamination in crops causes huge economic losses and may constitute a serious health threat. A practical use of compounds which can control aflatoxin production by fungi is expected to be an effective method to prevent aflatoxin contamination in agricultural products. Many kinds of aflatoxin production inhibitors have already been reported, and most of them are derived from plant constituents, microbial metabolites, or synthetic compounds. We have been searching for new aflatoxin production inhibitors among secondary metabolites produced by actinomycetes. In this review, the features of four aflatoxin production inhibitors, blasticidin A, blasticidin S, dioctatin A and polyoxins are introduced.

  The fungal strains belonging to Aspergillus section Nigri such as A. niger and A. tubingensis are industrially important microorganisms. However, some of Aspergillus section Nigri strains are known to produce mycotoxins. In this study, to confirm the non-production of four major mycotoxins (aflatoxins, ochratoxins, fumonisins, and patulin) by citric acid-producing Aspergillus tubingensis (formerly A. niger) WU-2223L, genome sequence analysis and LC-MS/MS analysis were performed. Although short genetic regions homologous to the biosynthetic gene clusters of ochratoxin A and fumonisin B₂ were found in the genome of strain WU-2223L, most of the other parts were missing, indicating that a large portion of the gene clusters were deleted. The genome sequence analysis also revealed that the genomic DNA of the strain WU-2223L possessed no gene homologous to biosynthetic gene clusters for aflatoxins and patulin in addition to ochratoxins and fumonisins. Moreover, the LC-MS/MS analysis on the broth of strain WU-2223L grown in three typical media revealed that none of the four mycotoxins were detected (below the detection limit). Therefore, the non-production of the four major mycotoxins by the strain WU-2223L was confirmed not only based on the genome sequence analysis, but also on the analysis of metabolites of the strain. Our findings indicate that A. tubingensis WU-2223L is a safe and promising strain that can be used for industrial production of valuable metabolites such as citric acid.

  Kojic acid is one of the major secondary metabolites produced by fungal species of Aspergillus section Flavi. In this study, we compared the extraction efficiency of kojic acid from agar media using the five solvents of different mixing ratio of methanol/water (100%, 75%, 50%, 25% and 0% of methanol), at two (low or high) kojic acid levels. The effect of ammonia exposure on the extraction efficiency was also examined. In all conditions tested, stable extraction was achieved by 100% methanol and 100% water, showing extraction efficiency of 75-86% with low standard deviations. The ammonia exposure did not affect the extraction efficiency when using above two solvents, indicating that 100% methanol or100% water is suitable rather than methanol/water mixture.

  Red yeast rice is made by growing Monascus on rice. Red yeast rice is used as a food all over the world. In recent years, red yeast rice has been increasingly used not only as a natural coloring agent, but also as a functional food with effects such as lowering blood pressure and lowering cholesterol. Monascus produces monacolin K and azaphilone pigments that affect human health, but it also produces citrinin, a mycotoxin believed to be harmful to health. Therefore, it is necessary to develop Monascus that does not produce the citrinin and can be used safely and securely as food. We conducted genome analyses of three Monascus strains using a next-generation sequencer and secondary metabolite analyses using LCMS. As a result, we found Monascus pilosus NBRC4520 and Monascus ruber NBRC4483 that do not produce the citrinin at the genome and LCMS analysis levels. Although Monascus ruber has been reported to produce citrinin from previous research reports, Monascus pilosus has been reported that biosynthetic genes for citrinin are not conserved in several strains at the genome level. Therefore, Monascus pilosus is considered the safest Monascus strain for use as food. Our goal is to contribute to the health of people around the world by studying safe and reliable Monascus for use in food.