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New Concept for Physiological Assessment of Yeast Cells
T. Imai and M. Mochizuki

At present, there are various methods for evaluating yeast viability and vitality. Yeast viability is a measure of the ratio of dead cells and yeast vitality is a measure of the vigor of living cells. All of the methods that evaluate yeast physiological condition measure only viability or vitality. Under real-world conditions such as actual brewing, however, viability and vitality are often unrelated. As a result, there is a fundamental problem with the current evaluation methods for vitality and viability. It is necessary to simultaneously observe both the dead cell ratio and vitality of living cells in order to precisely evaluate the physiological state of yeast. However, there have been no methods developed to resolve this fundamental problem to date. In this paper, a new method for simultaneously evaluating both viability and vitality is proposed using recent advances in flow cytometry; TO-PRO3 staining was applied for evaluation of viability and intracellular pH was applied for evaluation of vitality. First, the intracellular pH of yeast cells was measured using an argon laser, and the cell was determined to be dead or alive using a He/Ne laser. This new method was reproducible and could evaluate the subtle differences in viability and vitality that affect fermentation performance and beer quality. As this method could easily and accurately evaluate both viability and vitality of individual cells simultaneously, the fundamental problems with current evaluation methods were resolved. The simultaneous evaluation of both viability and vitality is essential for the brewing of quality beer.

Descriptors: yeast, vitality, viability, simultaneous evaluation, flow cytometer, intracellular pH, TO-PRO3

BrewingScience - Monatsschrift fr Brauwissenschaft, 69 (May/June 2016), pp. 33-41