Exploring Sake Flavor via RNA-Seq

The study, "Transcriptome Analysis of Sake Yeast in Co-Culture with Kuratsuki Kocuria," delves into how bacteria entering the sake fermentation process can impact the gene expression of Saccharomyces cerevisiae, ultimately influencing the flavor and quality of sake.

Sake is a traditional Japanese alcoholic beverage made from four key ingredients: koji, moto, rice, and water. Koji, produced by growing the mold Aspergillus oryzae on steamed rice, breaks down rice into sugars and amino acids but does not produce alcohol. The actual fermentation process is driven by moto, a fermentation starter made from a mixture of koji, rice, water, and Saccharomyces cerevisiae yeast. This yeast converts the sugars into ethanol, much like in beer and wine production.

The flavor and aroma of sake are primarily shaped by the esters and organic acids produced by the sake yeast. Different strains of yeast can create distinctive flavors, giving rise to a wide variety of sake profiles. Additionally, lactic acid bacteria can interact with yeast to further modify its metabolism, resulting in unique taste characteristics. Another important factor is the presence of kuratsuki bacteria, native to sake breweries, which naturally enter the brewing process and can influence sake's flavor by interacting with the yeast and adapting to the brewing environment. While research has focused extensively on sake yeasts, studies on kuratsuki bacteria are relatively new, revealing their role in shaping the final product's flavor.

Researchers co-cultured sake yeast (Saccharomyces cerevisiae) with Kuratsuki Kocuria to examine how the yeast’s gene expression profile is altered in this environment compared to monoculture. Using RNA sequencing enhanced by our rRNA depletion kits to remove unwanted rRNA (Saccharomyces cerevisiae riboPOOL kit), they observed significant changes in gene expression: 71 genes were upregulated more than twofold, and 61 genes were downregulated by half. Of note, stress-response genes, particularly those related to replication stress and meiosis, were significantly impacted. Furthermore, key metabolic genes, such as glyceraldehyde-3-phosphate dehydrogenase genes (TDH1, TDH2, TDH3), were downregulated.

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