RELATIONSHIP BETWEEN YEAST CELL PROLIFERATION AND INTRACELLULAR ESTERASE ACTIVITY DURING BREWING FERMENTATIONS

Flow cytometry was used for the determination of the intracellular esterase activity of unstressed and stressed Saccharomyces cerevisiae cells using fluorescein diacetate as substrate during brewing fermentations in EBC tubes. The determination of intracellular esterase activity by flow cytometry was compared with in vitro assays for determination of yeast esterase activity. The method was regarded valid with a high degree of reproducibility. Intracellular esterase activity during brewing fermentations was dependent on the yeast strain applied but independent of the wort compositions applied within this study. Further, the intracellular esterase activity during fermentation was correlated with cell proliferation determined by DNA staining and flow cytometry and by calculating the percentage of G1-phase cells. Yeast esterase activity in both unstressed and ethanol stressed cells followed a similar pattern during brewing fermentations. Furthermore, this pattern could be correlated with the percentage of G1-phase cells during fermentation indicating that the esterase activity was in some way related to cell cycle progression.