米曲霉是豆瓣酱发酵常用菌株,蛋白酶活力是评价成曲的重要指标。蛋白酶能将豆瓣原料中的蛋白质降解为寡肽以及氨基酸,为豆瓣酱风味提供重要前体物质,所以提高米曲霉的蛋白酶活力显得尤为重要。米曲霉BL18是1株具有较高蛋白酶活力的米曲霉菌株,将它应用在豆瓣酱发酵过程并与米曲霉3.042进行比较,同时通过基因组测序挖掘差异背后的遗传基础。与米曲霉3.042相比,米曲霉BL18成曲的孢子数达到4.19×108个/g干曲,酸性、中性和碱性蛋白酶活力分别提高52%、7.6%和45.6%;发酵前期米曲霉BL18蛋白酶具有优势,并且能将豆瓣酱鲜味氨基酸、甜味氨基酸总量分别提升33.3%和10.8%;基因注释结果表明米曲霉 BL18具有强大的能量合成、蛋白质合成及次级代谢产物合成能力,相比于米曲霉3.042,在米曲霉BL18中发现647个特有基因。米曲霉BL18在制曲发酵过程表现出的优势性能及大量功能基因的注释为其在豆瓣酱发酵应用中提供了有力的理论基础。
Aspergillus oryzae is commonly used as starter for the fermentation of broad bean paste, and protease activity is an important indicator of finished koji. Protease degrades the protein in raw materials into oligopeptides and amino acids, providing important precursors for flavor formation of broad bean paste, so it is particularly crucial to improve the protease activity of A. oryzae. A. oryzae BL18 is a strain with high protease activity. It was applied in the fermentation of broad bean paste and compared with A. oryzae 3.042, and simultaneously unearthed the genetic basis behind the differences through genome sequencing. Compared with A. oryzae 3.042, the spore number of finished koji made by A. oryzae BL18 reached 4.19×108/g dry weight, and the activities of acidic, neutral and alkaline protease increased by 52%, 7.6% and 45.6%, respectively. The protease of A. oryzae BL18 had advantages in the early stage of fermentation, and increased umami amino acid and sweet amino acid content in broad bean paste by 33.3% and 10.8%, respectively. Gene annotation results showed that A. oryzae BL18 had strong ability of energy synthesis, protein synthesis and secondary metabolite synthesis, at the same time, compared with 3.042, 647 unique genes were found in A. oryzae BL18 genome. The dominant performance of A. oryzae BL18 in koji making and fermentation and the annotation of a large number of functional genes provide a strong theoretical basis for its application in broad bean paste fermentation.
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