L. L. Chan (1), T. Smith (1), D. Kuksin (1), K. MCCULLEY (1); (1) Nexcelom Bioscience, Lawrence, MA, U.S.A
Technical Session 2 - Industrial Yeast Management
Sunday, June 14
2:00–3:15 p.m.
Fiesta 3,4,6,8
One of the major parameters measured in beer fermentation is the viability of yeast in the sample. Yeast viability can be monitored throughout fermentation to optimize brewing performance that may increase yield as well as produce consistent quality products. Recently, a novel imaging cytometry method has been demonstrated to rapidly and accurately measure yeast viability via fluorescent staining. The simplest fluorescent viability staining method utilizes propidium iodide (PI) to identify the dead yeast cells in the sample. By counting the total yeast cells in bright-field image and dead cells in PI fluorescence, one can accurately determine viability. However, single fluorescence may not be adequate for yeast in specialty beer where complex materials are added into the fermentation creating numerous background debris. The debris can cause inaccurate over-counting of total yeast cells, which can artificially generate higher viability. In this work, we developed a novel dual-fluorescence viability method using an acridine orange (AO) and PI nuclear staining technique. One of the most complicated samples is yeast with corn mash material, and by testing AO/PI with this sample, it can validate the capability of this staining method. Numerous fluorescent stains were examined before selecting AO and PI. In addition, a special buffer was used in order to increase the fluorescence signals generated by AO/PI. In order to validate the method, SYTO 9, CFDA, calcein AM, Calcofluor, AO, PI, ethidium bromide, and DAPI were tested with yeast in corn mash samples. Furthermore, the yeast viability was measured for a fermentation from 2 to 55 hours, and the results were compared to the manual counting methylene blue method. This viability method can be used with a variety of yeast samples that can produce accurate results for optimizing brewing fermentation process.
As a field applications specialist for Nexcelom Bioscience, Kelsey McCulley has had the pleasure of working with breweries of all sizes from Louisiana to Utah. Nexcelom's Cellometer image cytometry equipment provides a fast, simple, and accurate means to assess yeast viability and vitality for pitching and throughout the fermentation process. She is a member of the Master Brewers Association of the Americas. Kelsey received her B.S. degree in biomedical engineering from the Georgia Institute of Technology and her Ph.D. degree in bioengineering from Rice University in Houston, where she developed a taste for good Texas beer.
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