Dissolved carbon dioxide concentration profiles during very-high-gravity ethanol fermentation

The dissolved carbon dioxide (DCO2) evolved from Saccharomyces cerevisiae was measured for the duration of very-high-gravity (VHG) ethanol fermentation conducted at four glucose feeds (150, 200 +/- 0.21, 250 +/- 0.12, and 300 +/- 0.28 g/L). The DCO2 concentration profiles depict evolution patterns that depend on the extent of glucose utilized. A mass balance for DCO2 was proposed by taking into account the physiochemical behavior of CO2 and biological processes occurring under VHG ethanol fermentation conditions. The proposed equations could interpret the underlying CO2 desorption, CO2 conversion, and CO2 evolution on the basis of yeast activity during VHG ethanol fermentation. Consequently for 150 and 200 +/- 0.21 g glucose/L absence of yeast activity was interpreted in terms of zero CO2 evolution rate (CER(t)). In contrast, under 250 +/- 0.12 and 300 +/- 0.28 g glucose/L conditions the presence of non-zero residual glucose resulted in non-zero CER(t). The mass balance equation could also interpret that the physical desorption of CO2 from the fermentation broth did not follow the equilibrium relation between dissolved and off-gas CO2 concentrations as defined by Henry's law under current experimental conditions. (C) 2012 Elsevier B.V. All rights reserved.