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

Abstract

A correlation among different volumetric oxygen transfer coefficients (kLa) 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. Microaerophilic condition (kLa = 4.9h-1) have shown to be suitable when compared to complete anaerobiosis (kLa = 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. Different ORP values were found in anaerobiosis and kLa 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 O2 concentration.