Fermentation experiment
Seed cultures of strain K901 and 90 DNP-resistant sake yeast strains were inoculated in 5 ml of YM medium containing 10% glucose (YM10) [100 g/L (w/v) glucose, 5 g/L (w/v) polypeptone, 3 g/L (w/v) yeast extract, 3 g/L (w/v) malt extract] at 30°C for 24 h. Thirty microliters of precultured yeast strains were transferred to 50-ml Erlenmeyer flasks containing 30 ml of the YM10 medium. The yeast strains were statically grown at 30°C for 96 h. For time course analysis of fermentation products, the strain K901 and DNP-resistant strains DNPR38, DNPR46 and DNPR20 were cultured in 100 ml Erlenmeyer flasks containing 50 ml of the YM10 medium at 30°C.