Flow Cytometry for Age Assessment of a Yeast Population and its Application in Beer Fermentations

Michal Kuřec¹, Martin Baszczyňski¹, Radek Lehnert¹, André Mota², José A. Teixeira² and Tomáš Brányik^1,3
¹ Department of Fermentation Chemistry and Bioengineering, Institute of Chemical Technology, Technická 5, 166 28 Prague 6, Czech Republic.
² IBB - Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, University of Minho, Campus de Gualtar, 4710-057, Braga, Portugal.
³ Corresponding author. Email: tomas.branyik@vscht.cz.

J. Inst. Brew. 115(3), 253–258, 2009 | VIEW ARTICLE

ABSTRACT
An expeditious method of yeast age estimation was developed based on selective bud scar staining (Alexa Fluor 488-labelled wheat-germ agglutinin) and subsequent fluorescence intensity measurement by flow cytometry. The calibration curve resulting from the cytometric determination of average bud scar fluorescence intensities vs. microscopically counted average bud scar numbers of the same cell populations showed a good correlation and allowed routine cell age estimation by flow cytometry. The developed method was applied for yeast age control in traditional batch and continuous beer fermentations. At the pitching rates used in industrial beer fermentations, our results support former findings by locating a gradient of increasing yeast age from the top to the bottom zone of the fermenter cone. The results also indicate that in continuous beer fermentation, the increasing bud scar fluorescence of immobilized cells could help to schedule the replacement of aged biomass, prior to loss of viability or deterioration of process performance and product quality.

Key words:
aging, beer, bud scar, flow cytometry, staining, yeast.