Rethinking the cane sugar mill by using selective fermentation of reducing sugars by Saccharomyces dairenensis, prior to sugar crystallization

Abstract

Abstract High yield sugarcane is expected to resolve the competition between food and fuel regarding farmland and biomass resources. However, its higher composition of reducing sugars (i.e., glucose and fructose), which inhibit sucrose crystallization, hinders the production of sugar from high yield sugarcane. Under the conventional integrated sugar–ethanol manufacturing system, high biomass yield causes only the increase of ethanol production because of the increase in unrecovered sugar after extraction, which represents a failure in resolving the competition. The technology presented here is the world's first to solve this problem via selective ethanol fermentation using Saccharomyces dairenensis, an unconventional yeast that ferments only reducing sugars and leaves sucrose untouched. A laboratory-scale test using sugarcane juices with a high composition of reducing sugars (100 g kg−1) resulted in a sucrose crystal yield increase from a single extraction, from 16.2 to 65.1%, by introducing selective fermentation. The second extraction, from the molasses, which was enabled by the lowered residual reducing sugar composition, further enhanced the total sugar crystal yield (up to 83.4%). A simulation of the application of this technology in the U.S.A. revealed that both sugar and ethanol production were enhanced, whereas sugar production declined by the mere adoption of high yield cultivar, even with the increase in sugarcane yield.