Glucose Fermentation under Carbon Dioxide Pressure

The effect of CO2 pressure on commercial S.cerevisiae cells viability and on the rate of ethanol production in yeast, has been studied in batch cultures under 1,10 and 18 bar of CO2 pressures. The results show that the effect of CO2 pressure on ethanol productivity strongly depends on the temperature, glucose and starting biomass concentration and pressure itself. Under atmospheric CO2 pressure condition, fermentation was completed after 62 hours with a 10% (w w) of ethanol in the fermentation broth. In the same conditions, using up to 10 bar of CO2 pressure, ethanol productivity was about 8 % (w w). No productions were observed at a CO2 pressure of 18 bar, probably due to a complete failure of enzymatic activity. The fermentation was obtained starting from a high concentration of biomass, however no cellular growth was observed during the process, when 10 and 18 bar of CO2 pressure were used. Inositol addition, in the millimolar range concentration, greatly influenced the viability of yeast cells, allowing the production of ethanol more rapidly in the first 24 hours of fermentation. Nevertheless after 62 hours, the final ethanol concentration was lower than the ethanol obtained in the unsupplemented media. Finally, we demonstrated the feasibility of using a new pressurized reactor system, developed in our laboratory, for fermentation under higher carbon dioxide pressure.