Effect of pH Changes on the Measured RQ of Fermentations

Abstract

The respiratory quotient, or RQ, of a fermentation is: $$RQ = \frac{{CER}}{{OUR}}$$ where CER is the carbon dioxide evolution rate and OUR the oxygen uptake rate. As an indicator of metabolic state, the monitoring and control of the RQ is of interest. What can be calculated from gas analyses are the carbon dioxide transfer rate (CTR) and the oxygen transfer rate (OTR) across the gas-liquid interface. As oxygen is sparingly soluble in fermentation media, the rate of change in the dissolved oxygen concentration can never represent a large flux and hence the OTR and OUR are always equal in practical situations. The same is not true for carbon dioxide.