Yeast Biomass Quantification Microscopic
Fermentation processes are dependent on the use of microbial biomass and require quantification in terms of its biological and metabolic characteristics. The ethanol fermentation process is a fundamental example of bioprocess where production of ethanol is dependent on growth and metabolic activity of the yeast cells population. Fundamentally, quantification of yeast growth is critically dependent on enumeration of yeast cells and physiological state of these cells. In addition, the yeast biomass compositional analysis combined with quantification of metabolic activity of the yeast cell population provides for the detailed measured description of the yeast cells biomass properties in respect of the ethanol fermentation targets. Several quantification methods are available to allow for quantification of yeast cells population properties. However, due to the process dependent variable sample matrix a single method such as fast and simple optical density measurements is not often reliable and other methods often slower methods must be utilized.
Biomass Density Quantification:
- Microscopy - cell count number, viability and cell cycle
- Optical Density - spectroscopic biomass density measurment
- Flow Cytometry - cell count number, viability and cell cycle
Varius dyes can be used to differentiate the viability of the cells and their physiological status. One such example is Methylene Blue (MB) is a cationic thiazine dye with the systematic name 3,7-bis (Dimethylamino)phenazathionium chloride, Tetramethylthionine chloride C₁₆H₁₈ClN₃S or Methylene Blue hydrate C16H18ClN3S · xH2O. Methylene Blue is commonly used compound in biological and microbiological applications, such as the yeast cell counting procedures. MB is metachromatic stain that penetrates yeast cells and it is a redox-sensitive dye that interacts with cellular metabolism. Live (viable) yeast cells contain active metabolic enzymes (e.g., oxidases, reductases) that reduce methylene blue into a colorless form, meaning they appear unstained or faintly blue. Dead (non-viable) yeast cells lack active metabolism and cannot reduce the dye, so they remain dark blue.
To the left is the example of elctronic cell counter and how it can be use to microscopically enumerate yeast cells.