Presentation Information
[P02-166]Fermented food using Aspergillus oryzae seed-koji strains belonging to clade B
○Ken-Ichi Kusumoto1, Kanae Sakai1 (1. The University of Osaka (Japan))
Keywords:
Aspergillus oryzae,clade B,seed-koji strain,soybean paste,surface-ripened cheese
Aspergillus oryzae is widely used as koji mold (starter seed of fungi for food-grade) in traditional fermentation industries in Japan and East Asia for long centuries. Nowadays, over hundred strains of genome information for A. oryzae are registered in open database. Watarai et al. (DNA Research, 2019) reported that seed-koji strains are phylogenetically divided into eight clades. Recently, we found the phylogenetic tree of A. oryzae was available using part of genome information of A. oryzae, i.e., aflatoxin biosynthetic gene homolog cluster (K. Sakai et al., 2024). This phylogenetic tree was compatible with that of Watarai’s one.
Among them, we focused on the strains belonging to clade B that have unique characteristics in brewing soybean paste and cheese surface-ripened with koji mold. Commercially available soybean paste which contains added umami components, i.e., inosine monophosphate, is manufactured because of its convenience for consumers. It is manufactured with high-temperature-heat process after brewing. The reason for such heating process is the inactivation of acid phosphatase from koji mold to maintain inosine monophosphate. The acid phosphatase produced by koji mold hydrolyzes inosine phosphate to inosine, non-umami compound. By using A. oryzae KBN8048 belonging to clade B as starter strain for brewing soybean paste, we found that the high-temperature heating process can be skipped, and that mild heating can be applied instead (Horii et al., manuscript in preparation). The acid phosphatase AphC of A. oryzae functions mainly during koji under sufficient concentration of phosphoric acid. KBN8048 produces mutant AphC with low tolerance against heat and salt (K. Sakai et al., manuscript in preparation). Additionally, this strain produces considerable level of protease activity as that of commercial strain for soybean paste (Y. Horii et al., 2022). Therefore, the KBN8048 has unique enzymatic features suitable for manufacturing soybean paste keeping more inosine phosphate than general commercial strains with mild-heating condition, which is an energy saving process.
Meanwhile, A. oryzae C belonging to clade B was applied to manufacture cheese surface-ripened with koji mold. This strain produces considerably low level of lipase compared to tested commercial A. oryzae strains for traditional fermentation and Penicillium strains for ripening cheese. A. oryzae C did not produce detectable level of butyric acid in the cheese curd, suggesting that A. oryzae C has suitable characteristics to produce a less rancid and spicy curd (S. Suzuki et al., 2021).
In addition, the strains belonging to clade B are crnA deficient for nitrate incorporation (S. Miki et al., 2024). The relationship between crnA deficiency and above unique characteristics of clade B strains is not clear. It is possible that clade B strains accumulated several genetic variations. Nevertheless, it is suggested that these strains can be applied to brew new types of fermented foods by applying the above unique characteristics of A. oryzae strains in clade B.
Among them, we focused on the strains belonging to clade B that have unique characteristics in brewing soybean paste and cheese surface-ripened with koji mold. Commercially available soybean paste which contains added umami components, i.e., inosine monophosphate, is manufactured because of its convenience for consumers. It is manufactured with high-temperature-heat process after brewing. The reason for such heating process is the inactivation of acid phosphatase from koji mold to maintain inosine monophosphate. The acid phosphatase produced by koji mold hydrolyzes inosine phosphate to inosine, non-umami compound. By using A. oryzae KBN8048 belonging to clade B as starter strain for brewing soybean paste, we found that the high-temperature heating process can be skipped, and that mild heating can be applied instead (Horii et al., manuscript in preparation). The acid phosphatase AphC of A. oryzae functions mainly during koji under sufficient concentration of phosphoric acid. KBN8048 produces mutant AphC with low tolerance against heat and salt (K. Sakai et al., manuscript in preparation). Additionally, this strain produces considerable level of protease activity as that of commercial strain for soybean paste (Y. Horii et al., 2022). Therefore, the KBN8048 has unique enzymatic features suitable for manufacturing soybean paste keeping more inosine phosphate than general commercial strains with mild-heating condition, which is an energy saving process.
Meanwhile, A. oryzae C belonging to clade B was applied to manufacture cheese surface-ripened with koji mold. This strain produces considerably low level of lipase compared to tested commercial A. oryzae strains for traditional fermentation and Penicillium strains for ripening cheese. A. oryzae C did not produce detectable level of butyric acid in the cheese curd, suggesting that A. oryzae C has suitable characteristics to produce a less rancid and spicy curd (S. Suzuki et al., 2021).
In addition, the strains belonging to clade B are crnA deficient for nitrate incorporation (S. Miki et al., 2024). The relationship between crnA deficiency and above unique characteristics of clade B strains is not clear. It is possible that clade B strains accumulated several genetic variations. Nevertheless, it is suggested that these strains can be applied to brew new types of fermented foods by applying the above unique characteristics of A. oryzae strains in clade B.
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