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.