The objective of this study was to evaluate the effects of low temperature-adapted Saccharomyces cerevisiae Y297 and fermentation temperatures on the quality of Yakju brewed. Physicochemical properties of Yakju brewed were compared pH, total acidity, ethanol, free amino acid, organic acid contents, and volatile flavor compounds in S. cerevisiae Y297 with control treatment. Cooked non-glutinous rice and saccharogenic amylase in koji were mixed with ethanol-producing yeasts and then fermented at 15℃, 20℃, and 25℃ for 20 days. Yakju brewed using the Y297 treatment showed the highest ethanol yield (17.9%) at 20℃. Expression of heat shock protein (HSP) 104 was evaluated by immunoblotting as an indication of adaptation to low temperatures (15℃); levels of the HSP104 protein were higher in the Y297 treatment than in the control. Organic acid analysis showed that the lactic acid content of Yakju brewed using the control was the highest at 25℃. Finally, free amino acid analysis showed that the Y297 treatment had a higher proportion of essential amino acids than the control. Overall, these results indicate that S. cerevisiae Y297 could be used as a suitable yeast for Yakju brewed under low temperature (15℃) condition.

The objectives of this study were to isolate and characterize low temperature adaptation yeast and to obtain suitable yeasts strains for manufacturing Yakju. In this study, we isolated 482 wild yeasts from fermented foods. Out of these, 5 yeast strains were selected based on increased growth at low temperature (15℃) and high β-glucosidase activity. To screen the aromatic level of isolates, media containing cerulenin and 5,5,5-trifluor-DL-leucine (TFL) were used. Y297 strain demonstrated tolerance against TFL and produced more than 13% alcohol. Y297 strain was identified a Saccharomyces cerevisiae based on the 26S rDNA gene sequences. Maximum cell growth was observed after 19 hr and 38 hr of incubation at 25℃ and 15℃, respectively. The exponential phase was followed by a lengthy stationary phase, at 15℃, when the cells remained high viable. Y297 strain demonstrated tolerance against alcohol (10%), glucose (60%) and salt(NaCl, 8%). β-glucosidase and esterase activity in Y297 were higher than those of controls at 15℃. Overall, these results indicated that using wild yeast strain, isolated from fermented food, affects the chemical characteristics of the brewed Yakju.