Determination of Yeast Viability Using Fluorophores

The assessment of pitching and cropping yeast viability and vitality is important in attaining adequate fermentation performance. Methylene blue remains an industry standard for viability assessment, even though the efficiency of this stain is highly controversial. It has been suggested that methylene violet might provide a more accurate and reproducible assessment of viability than does methylene blue because of impurities in the latter. The objective of this study was to identify an alternative viability assessment to brightfield reductive dye techniques using fluorophores. Viability studies were performed on yeast cell populations exhibiting different viabilities and stresses. Viability was determined using fluorophore dyes, such as oxonol (DiBAC4(3)), 1-anilino-8-naphtalene-sulfonic acid (MgANS), berberine, Sytox Orange, propidium iodide, FUN1, and conventional brightfield dyes, such as methylene violet. It was observed that oxonol successfully distinguished between live and dead cells without ambiguity. In addition, with the exception of FUN1, fluorophore staining was perceived to be less subjective to the operator compared with brightfield dye staining because of the lack of intermediate color variations.