Flow cytometry for age assessment of a yeast population and its application in beer fermentations

摘要

An expeditious method of yeast age estimation was developedbased on selective bud scar staining (Alexa Fluor 488-labelledwheat-germ agglutinin) and subsequent fluorescence intensitymeasurement by flow cytometry. The calibration curve resultingfrom the cytometric determination of average bud scar fluorescenceintensities vs. microscopically counted average bud scarnumbers of the same cell populations showed a good correlationand allowed routine cell age estimation by flow cytometry. Thedeveloped method was applied for yeast age control in traditionalbatch and continuous beer fermentations. At the pitchingrates used in industrial beer fermentations, our results supportformer findings by locating a gradient of increasing yeast agefrom the top to the bottom zone of the fermenter cone. The resultsalso indicate that in continuous beer fermentation, the increasingbud scar fluorescence of immobilized cells could helpto schedule the replacement of aged biomass, prior to loss ofviability or deterioration of process performance and productquality.