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

Objective A 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. Results Microaerophilic condition (k L a = 4.9 h −1 ) have shown to be suitable when compared to complete anaerobiosis (k L a = 0), providing an ethanol yield and a productivity after 48 h of 64.3% and 0.45 g ethanol L −1 h −1 , respectively; the maximum ethanol titer obtained was 21.50 g ethanol L −1 . Values of ORP varying from − 270 to − 330 mV resulted in high ethanol production from xylose by S. stipitis. Conclusions Different ORP values were found in anaerobiosis and k L a 4.9 h −1 , suggesting that for ethanol production by S. stipitis , values from − 270 to − 330 mV 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.