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

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.

Characteristic features of the unique house sake yeast strain Saccharomyces cerevisiae Km67 used for industrial sake brewing.

For several decades, almost all sake has been brewed with sake yeast Saccharomyces cerevisiae Kyokai no. 7 (K7) group strains. Although the widespread use of these strains has contributed to sake quality improvement, it may have lessened the diversity of sake gustatory properties brought about by house sake yeast (indigenous yeast of sake brewery). Sake yeast S. cerevisiae strain Km67 derives from the house yeast strain of Kiku-masamune Sake Brewing Co., Ltd., and it has been playing a central role in industrial sake brewing for decades. By using DNA sequencing, we revealed that strain Km67 does not possess specific loss-of-function mutations of stress response-related genes, which are characteristic of K7 group strains. Km67 had higher stress tolerance than K7 group strains likely because of the more efficient function of the stress response and heat shock elements in this strain. Sensory evaluation and taste sensor analysis demonstrated that sake brewed with Km67 had characteristically thicker body than sake brewed with K7 group strains. Chemical analysis suggested that unique sensory properties of the sake brewed with Km67 were due to high citramalic acid concentration. Taken together, these results revealed that strain Km67 differs from K7 group strains by genetic background and confers unique chemical composition and taste qualities upon sake it generates. It is expected that sake quality and gustatory properties will be diversified by utilizing house yeast such as strain Km67.

Antifungal properties of Japanese cedar essential oil from waste wood chips made from used sake barrels.

In this study, we prepared essential oil (EO) from waste wood chips made from used sake barrels (USBs) of Japanese cedar (i.e., EO-USB) by steam distillation. We found that EO-USB and three commercially purchased EOs derived from xylem tissue of Japanese woods, such as Japanese cedar (Cryptomeria japonica), Japanese cypress (Chamaecyparis obtusa) and false arborvitae (Thujopsis dolabrata), suppressed fungal growth activity against Trichophyton rubrum, which is the cause of tinea disease. The magnitude of the suppressive effects of the EOs ranked as follows: T. dolabrata > USB = C. japonica > C. obtusa. These EOs also inhibited the activity of DNA polymerase in an extract from T. rubrum mycelia with the following ranking: T. dolabrata > USB = C. japonica > C. obtusa. In addition, 50 µg/ml of EO-USB showed antifungal properties, killing T. rubrum mycelia at 27-42˚C in 20 min. By gas chromatography/mass spectrometry analysis, the main sesquiterpenes in EO-USB were δ-cadinene (25.94%) and epi-cubenol (11.55%), and the composition of EO-USB was approximately the same as that of EO-C. japonica. Three prepared sesquiterpenes, δ-cadinene, epi-cubenol and ß-eudesmol, inhibited the fungal growth and DNA polymerase activities of T. rubrum, and epi-cubenol showed the strongest inhibition among the compounds tested. These sesquiterpenes had no inhibitory effects on the activities of other DNA metabolic enzymes, such as DNA topoisomerase II, IMP dehydrogenase, polynucleotide kinase and deoxyribonuclease from T. rubrum. Taken together, these results suggest that EO-USB containing epi-cubenol may be useful for its anti-tinea disease properties, which are based on DNA polymerase inhibition.