Profiling of taste-related compounds during the fermentation of Japanese sake brewed with or without a traditional seed mash (kimoto)

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Japanese sake production involves three processes: rice koji fermentation, seed mash fermentation, and main mash fermentation. Traditional seed mash (kimoto) production utilizes natural lactic acid produced by lactic acid bacteria for pure cultures of only sake yeast, preventing the growth of wild yeast and other unwanted bacteria. Recently, because kimoto production requires substantial time and labor, sake yeast mass-cultured in usual liquid medium has been used as a seed mash alternative. Sake quality is highly similar to that of kimoto, suggesting that they share similar component profiles. However, comparative component analyses of sake brewed with kimoto and sake brewed with cultured yeast are lacking. In this study, a time-course analysis of hydrophilic compounds in the main mash brewed with kimoto and with cultured yeast as well as a sensory evaluation of the products were performed. As a result, differences in various compounds and in umami taste level between sake brewed with kimoto and cultured yeast were detected. This is the first comparative analysis of changes in the component profile during sake main mash brewing using kimoto seed mash and cultured sake yeast; our results clarify the effects of kimoto seed mash on main mash brewing and sake quality.

Section snippets

Sake brewing

Kimoto and the main mash for sake brewing were produced at an industrial scale at the Kiku-Masamune sake brewing factory by conventional methods.

Yeast strain

The non-foaming sake yeast S. cerevisiae Km67 is a house stock derived from the ATCC32694 strain isolated from Kiku-Masamune sake mash between 1966 and 1973 (5).

Chemical reagents

Trichloroacetic acid (TCA) was purchased from Fujifilm Wako Pure Chemical Industries, Ltd. (Osaka, Japan).

Sampling

Kimoto or main mash for sake brewing were centrifuged (19,200 × g, 4 °C, 10 min). For

Results and discussion

A time-course analysis was performed using two types of main mashes, i.e., brewed using kimoto seed mash or using cultivated sake yeast. The sake yeast was S. cerevisiae Km67, a house yeast strain at the Kiku-Masamune sake brewing factory traditionally used for the production of kimoto sake (5). Amino compounds in main mash samples were broadly analyzed by LC–MS and hydrophilic compounds, such as organic acids and sugars, were comprehensively evaluated by GC–MS.

Acknowledgments

This work was supported by JSPS KAKENHI Grant Number 18J20256 (MT) and 17K19235 (EF). The study represents a portion of the dissertation submitted by Moyu Taniguchi to Osaka University in partial fulfillment of the requirement for her Ph.D. The authors declare no conflict of interest.

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