Effect of Carbon and Nitrogen Additions on Consumption Activity of Apparent Extract of Yeast Cells in a Brewing Process

摘要

In our study, low-amino―nitrogen wort was used with glucose, maltose, and maltotriose as the major assimilating sugars, and the effects of the addition of carbon and nitrogen sources on the sugar-uptake capability and the production rate of ethanol in yeast cells were investigated. The apparent extract concentration, which was defined as an estimated value of the concentration of the total amount of dry matter in the wort based on the measured value of specific gravity of wort, was used as an indicating variable for the degree of fermentation (DF) in our study. When the ratio of glucose to maltose was changed, no marked effect on the rate of decrease in the apparent extract concentration was found. Maltose and maltotriose uptake by the cells apparently was inhibited at a high glucose concentration. The addition of nitrogen sources, particularly aspartate (Asp), most effectively enhanced the consumption activity of the extract. When the apparent extract concentration decreased from 14% (the initial apparent extract concentration) to 3.5%, i.e., when the DF reached 75%, the fermentation time was shortened to 72% of that of the control experiment by adopting a strategy of intermittent addition of Asp. Asp addition also enhanced both the cell growth and the maltose-uptake capability.