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ABSTRACT: Koji mold, classified in the genus Aspergillus, is used to produce traditional Japanese fermented foods such as miso, soy sauce, and sake. In recent years, the application of koji mold to cheese ripening has attracted attention, and cheese surface-ripened with koji mold (koji cheese) has been studied. In this study, to evaluate the taste characteristics of koji cheese, an electronic tongue system was employed to measure the taste values of cheese samples ripened using 5 strains of koji mold in comparison with commercial Camembert cheese. All koji cheese samples exhibited lower sourness and greater bitterness, astringency, saltiness, and umami richness than the Camembert cheese samples. The intensity of each taste characteristic differed depending on the koji mold strain. These results indicate that koji cheese has a different taste value than conventional mold-ripened cheese. Furthermore, the results also indicate that various taste characteristics can be achieved by selecting different koji molds.

Aspergillus flavus produces aflatoxin, a carcinogenic fungal toxin that poses a threat to the agricultural and food industries. There is a concern that the distribution of aflatoxin-producing A. flavus is expanding in Japan due to climate change, and it is necessary to understand what types of strains inhabit. In this study, we sequenced the genomes of four Aspergillus strains isolated from agricultural fields in the Ibaraki prefecture of Japan and identified their genetic variants. Phylogenetic analysis based on single-nucleotide variants revealed that the two aflatoxin-producing strains were closely related to A. flavus NRRL3357, whereas the two non-producing strains were closely related to the RIB40 strain of Aspergillus oryzae, a fungus widely used in the Japanese fermentation industry. A detailed analysis of the variants in the aflatoxin biosynthetic gene cluster showed that the two aflatoxin-producing strains belonged to different morphotype lineages. RT-qPCR results indicated that the expression of aflatoxin biosynthetic genes was consistent with aflatoxin production in the two aflatoxin-producing strains, whereas the two non-producing strains expressed most of the aflatoxin biosynthetic genes, unlike common knowledge in A. oryzae, suggesting that the lack of aflatoxin production was attributed to genes outside of the aflatoxin biosynthetic gene cluster in these strains.

ABSTRACT: More than 2,000 varieties of cheese currently exist in the world, and cheese manufacture continues to flourish. To develop the cheese ripening process, additional ingredients are used during cheese production. In this study, the effect of sake lees as an additional ingredient on the fermentation of cheese using Aspergillus oryzae (koji mold), known as koji cheese, was investigated. Aspergillus oryzae is used in the fermentation of Japanese traditional foods, such as sake and soy sauce, given its strong enzymatic activities, as well as in cheese production (i.e., koji cheese). Sake lees, a by-product of the fermentation of rice with A. oryzae and yeasts in the sake brewing process, contains various metabolites, such as amino acids. Here, supplementation with sake lees enhanced the activities of lactic acid bacteria and affected the color of the cheese. Metabolome analysis revealed that sake lees altered the balance of carbohydrates and fatty acids in the cheese. Remarkably, supplementation with sake lees enhanced the production of umami-enhancing γ-glutamyl (kokumi-active) peptides. This study suggests that a new type of cheese can be produced using A. oryzae and sake lees, and information on the synergistic effects of A. oryzae and sake lees will aid the development of cheese production.

The regulation of enzyme activity in the production of various fermented foods using koji mold has been optimized in many ways, and few additional refinements are apparent. This study examined light as a modifiable factor with which to adjust the enzyme activities of koji. A previous study has shown improved saccharification of wheat bran with Aspergillus oryzae RIB40 under at least 8 h of darkness. In the work reported here, light exposure had no significant effect on the saccharification activity of A. oryzae RIB1187. However, light exposure for 8 h or more continuously decreased protease-specific activity in RIB1187, as was seen previously in RIB40. This information may help manufacturers to improve fungal enzyme production, processes, and facilities. [ABSTRACT FROM AUTHOR]