Production of xylitol from a mixture of hemicellulosic sugars

Abstract

Materials and methods are described to produce xylitol from a mixture of hemicellulosic sugars by several routes. Examples include either as a direct co-product of a biorefinery or ethanol facility, or as a stand-alone product produced from an agricultural or forestry biomass feedstock including using, e.g. ethanol waste streams.

1 . A method to produce xylitol from a mixture of hemicellulosic sugars. 
     
     
         2 . The method to produce xylitol of  claim 1 , comprising converting xylose alone to xylitol by the action of a xylose reductase. 
     
     
         3 . The method to produce xylitol of  claim 1 , comprising conversion of L-arabinose to xylitol and reducing xylose. 
     
     
         4 . The method to produce xylitol of  claim 1 , comprising reducing D-xylose and metabolizing arabinose. 
     
     
         5 . A microorganism capable of converting a mixture of sugars, wherein the sugars are selected from the group consisting of xylose, arabinose, and combinations thereof, and wherein conversion is by fermentation to xylitol with little or no arabitol present in the final fermentation broth. 
     
     
         6 . The microorganism of  claim 5 , wherein the microorganism is an  E. coli  strain that efficiently produces xylitol from D-xylose, using a mutant xylose reductase (XR) designated VMQCI and a genetically engineered  E. coli  that utilizes L-arabinose as a carbon source, thereby decreasing L-arabinitol production, and wherein xylitol is produced at a purity of approximately 100% from an equivalent mixture of D-xylose, L-arabinose, and D-glucose, and wherein there is a minimal production of L-arabinitol byproduct. 
     
     
         7 . The microorganism of  claim 6 , wherein the  E. coli  strain is designated HZ 1434. 
     
     
         8 . The microorganism of  claim 5 , wherein arabitol is less than 10% of the final mixture of polyol products produced. 
     
     
         9 . The microorganism of  claim 5 , wherein arabitol is less than 5% of the final mixture of polyol products produced. 
     
     
         10 . The microorganism of  claim 5 , wherein an initial ratio of xylose:arabinose is greater than 1:1. 
     
     
         11 . The microorganism of  claim 5 , wherein an initial ratio of xylose:arabinose is greater than 2:1. 
     
     
         12 . An  E. coli  strain designated ZUC220. 
     
     
         13 . An  E. coli  strain designated ZUC 170. 
     
     
         14 . A bioprocess for converting a mixture of sugars to xylitol, wherein the mixture includes sugars selected from the group consisting of xylose, arabinose, and combinations thereof, and wherein xylitol is produced with little or no arabinitol present in the final fermentation broth. 
     
     
         15 . The bioprocess of  claim 14 , wherein arabinitol is less than 10% of the final mixture of polyol products produced.