STUDY OF THE METABOLIC ACTIVITY OF YEASTS USED IN BREWING INDUSTRY AND BIOETHANOL PRODUCTION
Determination of the percent of actively fermenting yeasts, during the production, can be used for optimization of the fermentation process in brewing industry and bioethanol production. The metabolic activity of brewing yeasts and yeasts used in bioethanol production was investigated using carboxyfluorescein diacetate (cFDA). cFDA penetrates the cell membrane, then active esterase enzymes inside the cell cleave acetate residues, and the released fluorescein stains the cell in green. The stained cells were counted by new fluorescent image cytometry EasyCounter YC from Milkotronic. EasyCounter YC is based on a fluorescence microscopic cell counting technique. Due to the fluorescent dye, LED optics, and CCD capture technologies, cell analysis is accurate, reliable, and fast. Optimal concentrations of the cFDA reagent for both types of yeast were determined. The cFDA optimal concentration for metabolic activity determination of the brewing yeast was found to be 50 μg/mL, and for yeasts in bioethanol production was found to be 200 μg/mL. The metabolic activity of cell suspensions with different concentrations of dead and live cells was determined. It was found that the assay provides very valuable information when the percentage of dead cells in the sample is significant, because there are a large number of cells with weak enzymatic activity in the suspension at that stage. The same samples were simultaneously tested for determination of total cell count, dead cell count and the percentage of viability. Great correlation between the individual parameters was established.
