The production of value-added co-products from agricultural biomass is an important economic driver for the success of a biorefinery approach to the production of ethanol and other fuels. During most ethanol production methods significant amounts of hemicellulose by-products are produced which are rich in pentoses such as xylose and arabinose as well as other sugars. Xylitol, a five-carbon polyol that has gained acceptance as a natural food sweetener, can be made from pure xylose by chemical hydrogenation, but production from a mixed pentose stream such as that found in hemicellulose is difficult and expensive due to separation issues. We have developed high efficiency fermentation strains capable of converting xylose and arabinose to xylitol by combining a variety of microbial genes and pathways. The fermentation is carried out in an engineered E. coli which also utilizes the other sugars in the mixture as carbon sources, thus producing xylitol with no other competing polyol by-products produced. The increasing demand for xylitol volume should provide a unique match as a co-product made alongside ethanol and other fuels produced from a biorefinery.

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