Anaerobic Yeast Fermentation Using Redox ControlSource: Eppendorf, Inc
Metabolic activity of microorganisms depends on many factors, including oxidation and reduction reactions, or the “redox potential” of the culture environment. Redox reactions govern metabolism of biologically important nutrients such as carbon, hydrogen, oxygen, nitrogen and sulfur. Measuring their redox potential allows the fermentor operator to monitor the addition of reducing or oxidation agents, while ensuring that the potential is in the proper range for cell growth, especially when the DO level is very low.
Since free electrons never exist in any noteworthy concentration, reduction and oxidation reactions are always coupled together, and can be considered a measure of the ease with which a substance either absorbs or releases electrons. The determination of redox potential is a potentiometric measurement, expressed as millivolts (mV). Practically, however, no electrical current flows through the sample solution during this potential measurement.
Redox sensors are most commonly used to maintain anaerobic conditions in a fermentation broth. They can be used to measure trace amounts (< 1 ppm) of dissolved oxygen, at levels that are too low for the DO sensors in various anaerobic fermentation processes. Glucosecontaining feed medium can be treated as a reducing source in oxidation-reduction of the culture medium. When the oxidation capacity is increased, the redox potential level will elevate to a higher value. On the flip side, its value will become lower when the culture broth has a higher reducing capacity.