Development of redox potential-controlled schemes for very-high-gravity ethanol fermentation

Abstract

Fermentation redox potential reflects the momentary physiological status of organisms. Controlling redox potential can modulate the redistribution of intracellular metabolic flux to favor the formation of the desired metabolite. Accordingly, we have developed three redox potential-controlled schemes to maximize their effects on the very-high-gravity (VHG) ethanol fermentation. They are aeration-controlled scheme (ACS), glucose-controlled feeding scheme (GCFS), and combined chemostat and aeration-controlled scheme (CCACS). These schemes can maintain fermentation redox potential at a prescribed level (i.e., −50, −100, and −150mV) by supplementing sterile air, fresh glucose media, or a combination of sterile air and fresh glucose media into a fermenter to counteract the decline of redox potential due to yeast growth. When ACS was employed, the fermentation efficiency at −150mV is superior to the other two redox potential levels especially when the initial glucose concentration is higher than 250g/l. The redox potential-controlled period for ACS, GCFS, and CCACS at −150mV under the same 200g glucose/l condition was 2.5, 21.7 and 64.6h and the corresponding fermentation efficiency was 85.9,89.3 and 92.7%, respectively.