Properties of <i>Aspergillus oryzae</i> strains isolated from natural fields and the evaluation of their potential as seed <i>koji</i> for sake

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  • TSUBOI Hazuki
    Department of Materials Engineering, National Institute of Technology (KOSEN), Nagaoka College
  • WADA Yuko
    Department of Materials Engineering, National Institute of Technology (KOSEN), Nagaoka College
  • KOJIMA Ayano
    Department of Materials Engineering, National Institute of Technology (KOSEN), Nagaoka College
  • NAGAI Yutaka
    Niigata Meijo Co., Ltd.
  • TASAKI Yuji
    Department of Materials Engineering, National Institute of Technology (KOSEN), Nagaoka College

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Other Title
  • 自然界から分離した黄麹菌<i>Aspergillus oryzae</i>の諸性質と清酒用種麹としての適性評価
  • 自然界から分離した黄麹菌Aspergillus oryzaeの諸性質と清酒用種麹としての適性評価
  • シゼンカイ カラ ブンリ シタ キ コウジキン Aspergillus oryzae ノ ショ セイシツ ト セイシュヨウシュ コウジ ト シテ ノ テキセイ ヒョウカ

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<p>Aspergillus oryzae produces important hydrolytic enzymes during the sake brewing process. The hydrolysates are used for alcoholic fermentation by sake yeast and affect the flavor of sake. Here, we isolated novel wild strains of A. oryzae and evaluated them for their potential as seed koji for sake to increase the diversity of A. oryzae strains for producing sake. Thirteen filamentous A. oryzae-like fungi were isolated from fields at the National Institute of Technology (KOSEN), Nagaoka College and grown on rice-wood ash-potassium phosphate medium. All isolates were identified as A. oryzae using morphological characteristics, aflatoxin (AF) production, DNA sequence analysis of the rDNA 5.8S-ITS region and AF biosynthesis homologous genes, and estimation of α-amylase gene copy number. Enzyme activities, which are important during sake brewing, were measured in rice koji prepared using each of the isolates and three control strains, including two commercial seed koji. The 13 isolates showed α-amylase and glucoamylase activities approximately equal to or higher than those of the two commercial seed koji, suggesting that the 13 isolates can be used as seed koji for sake. Furthermore, the production ratio of glucoamylase to α-amylase, one of the indices of high-quality koji, was higher in 12 isolates, except in the strain NKK9, than in the two commercial seed koji. Therefore, the 12 isolates described in this study could be used as seed koji for brewing high-quality sake.</p>

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