The Influence of Controlling Redox Potential on Ethanol Production by Saccharomyces cerevisiae

The influence of redox potential (ORP) on ethanol production by Saccharomyces cerevisiae was investigated. The steady ORP levels (-50 mV, -100 mV, -150 mV, -230 mV) were obtained by modulating agitation speed and aeration rate continuously during the fermentation processes. The results showed that the ORP level had a notable influence on cell growth, yield of ethanol, formation of glycerol, secretion of organic acids, and death rate of cells. The biomass of culture with ORP controlled at −50 mV, which had the lowest death rate of cells, was 1.26, 1.86, and 2.59 times that of the culture with ORP at −100 mV, −150 mV, and −230 mV respectively, and the final glycerol concentration was 1.2, 1.1, and 1.7 times, but the final ethanol concentration was 0.87, 0.49, and 0.51 times as compared to the other three ORP levels. It was observed that ORP level of -150 mV was most favorable to ethanol production, considering all the factors, biomass, ethanol yield, glycerol production, and the final residual glucose concentration which could not be consumed by yeast in the broth. The results also implied that on the bioreactor scale, tuning up the ORP level was a powerful tool to exactly control the behavior of ethanol fermentation.