Tuesday, April 20, 2010
8-34

Development of a method for isolation and identification of xylodisaccharides

Heidi M. Pilath1, William E. Michener1, David K. Johnson2, Mark R. Nimlos1, and Michael E. Himmel2. (1) National Bioenergy Center, National Renewable Energy Laboratory, 1617 Cole Blvd, MS3323, Golden, CO 80401, (2) Biosciences Center, National Renewable Energy Laboratory, 1617 Cole Blvd., Golden, CO 80401

In acid pretreatment of biomass the hemicellulose is hydrolyzed to form fermentable sugars and expose the cellulose for subsequent hydrolysis by enzymes.  A key to the economic success of ethanol production is the hydrolysis of xylan to give monomeric xylose in high yield.  Xylose yield is reduced by dehydration reactions, which form furfural, as well as reversion reactions which result primarily in the formation of xylodisaccharides.   Earlier studies demonstrated that at high sugar loadings, reversion product yields approached 9% for xylose.  To-date there has been limited research to identify the precise structure of the disaccharides.  A major hurdle is that there are no commercial standards available for the reversion products from xylose, other than xylobiose.  The purpose of this study was to identify the xylodisaccharides formed from xylose reversion reactions.  To that end, linkage analysis of the unknown xylodisaccharides was achieved by first fractionating the xylodisaccharide mixture into its individual components by preparative LC, followed by Hakamori Methylation, and then GC/MS to identify linkage types. NMR analysis was also conducted on the individual components to verify the linkages.  Underivatized sample fractions were collected and analyzed by LC/MS to obtain fragmentation patterns and retention times of the identified xylodisaccharides.   Overall, we hope through this work to gain insight into limiting the formation of xylodisaccharides during dilute acid pretreatment of biomass at high solid loadings.

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