Dehydrogenase activity measurement in yeast fermentation

Abstract

The dehydrogenase activity was used as a measure of active biomass in preference to other biochemical parameters because of the simple, but accurate nature of the dehydrogenase test. After a consierable amount of experimental work on the dehydrogenase activity measurement technique and the consideration of utilization of the technique as a measure of the active biomass in yeast fermentation systems, an analytical procedure was developed. The developed procedure was first tested on two yeast cultures (Kluyveromyces fragilis andCandida pseudotropicalis) and then used for the determination of active yeast cells in single-cell protein reactors operating on cheese whey. The dehydrogenase enzymes appeared to be sensitive to the pH, the optimum being 7±0.2. Because the optimum pH for the propagation of these yeasts is about 4.5±0.2 and a pH variation of 3 U impairs enzyme activity, the pH of the medium must be adjusted. The incubation time is also a critical factor in determining the accuracy of the TTC test, especially at low-biomass concentrations. An incubation period of 80 min was found to be reasonable.