Sunday, April 29, 2007

Fluorometric method for the quantitation of active yeast cells

Darby D. McLean, J.B. Somes, Tawnya St. Pierre, and J. Fleming. GenPrime, Inc., 157 S. Howard Ste #605, Spokane, WA 99201

Yeast performance is critical to proper fermentation attenuation.  For this reason, methods of yeast analysis are an important element of the fermentation process.  Traditional methods including hemacytometer counting and methylene blue staining are rapid, but inaccurate and unreliable. Slide culture is an accurate measure of yeast viability, but requires a lengthy incubation period of 18 to 24 hours. As an alternative, we have developed a fluorometric assay, the Easy Count, based on the metabolic activity of the yeast culture to provide operators with a rapid and accurate estimation of active cell number.  This method was compared to the hemacytometer counting technique as an estimation of cell number, and to both methylene blue staining and slide culture as measures of vitality and prediction of fermentation performance. The Easy Count method correlated to the hemacytometer, methylene blue, and slide culture with R2 values of .985, .987, and .962 respectively, P<.0001.  An error analysis was carried out on the Easy Count, hemacytometer and methylene blue staining techniques during fermentation for multiple operators performing the tests. There was significantly less error associated with the Easy Count than with the microscopic methods.  The Easy Count was also used to track the activity of a culture during fermentation. These results suggest that this novel method can be used to determine the active number of cells in a commercial ethanol plant. Thus, the Easy Count could be used to determine correct innoculation rates, monitor fermentation and propagation progression, and for other applications involving cell quantitation.

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