Online monitoring of the redox potential in microaerobic and anaerobic Scheffersomyces stipitis fermentations

ObjectiveA correlation among different volumetric oxygen transfer coefficients (k(L)a) and the oxireduction potential (ORP) in batch fermentations using Scheffersomyces stipitis was evaluated. Experiments were performed using a mixture of xylose and glucose as the substrates.ResultsMicroaerophilic condition (k(L)a=4.9h(-1)) have shown to be suitable when compared to complete anaerobiosis (k(L)a=0), providing an ethanol yield and a productivity after 48h of 64.3% and 0.45g ethanol L-1 h(-1), respectively; the maximum ethanol titer obtained was 21.50g ethanol L-1. Values of ORP varying from -270 to -330mV resulted in high ethanol production from xylose by S. stipitis.ConclusionsDifferent ORP values were found in anaerobiosis and k(L)a 4.9h(-1), suggesting that for ethanol production by S. stipitis, values from -270 to -330mV are favorable under the studied circumstances. In this ORP range, the greatest rates of xylose consumption and ethanol production were registered. ORP monitoring was demonstrated to be a suitable option for online control throughout the fermentation processes, which may provide a more efficient bioprocess operation with a very low O-2 concentration.