Redox potential-driven repeated batch ethanol fermentation under very-high-gravity conditions

When Saccharomyces cerevisiae was cultivated under similar to 200 g glucose/l condition, the time point at which glucose was completely utilized coincided with the moment at which the slope of a redox potential profile changed from negative or zero to positive. Based on this feature, a redox potential-driven glucose-feeding fermentation operation was developed, and resulted in a self-cycling period of 14.25 +/- 0.4 h. The corresponding ethanol concentration was maintained at 88.4 +/- 1.0 g/I with complete glucose conversion, and the cell viabilities increased from 80% in the transition period to 97.2 +/- 1.1%, implying the occurrence of yeast acclimatization. In contrast, a pre-determined 36-h manually adjusted period was chosen to oscillate yeast cells under similar to 250 gglucose/l conditions, which resulted in 106.76 +/- 0.7 g ethanol/l and 15.19 +/- 1.3 g glucose/I remaining at the end of each cycle. Compared to the equivalent batch and continuous ethanol fermentation processes, the annual ethanol productivity of the reported fermentation operation is 2.4% and 13.2% greater, respectively in similar to 200g feeding glucose/I conditions. (C) 2011 Elsevier Ltd. All rights reserved.