ARS | Publication request: Liquid chromatography-mass spectrometry investigation of enzyme-resistant xylooligosaccharide structures of switchgrass associated with ammonia pretreatment, enzymatic saccharification, and fermentation

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 13, 2012
Publication Date: January 28, 2012
Citation: Bowman, M.J., Dien, B.S., Hector, R.E., Sarath, G., Cotta, M.A. 2012. Liquid chromatography-mass spectrometry investigation of enzyme-resistant xylooligosaccharide structures of switchgrass associated with ammonia pretreatment, enzymatic saccharification, and fermentation. Bioresource Technology. 110:437-447.

Interpretive Summary: BBiomass from dedicated energy crops (e.g., switchgrass) represents a source of renewable material for conversion to ethanol and other liquid biofuels. The conversion of biomass to simple monosaccharides, required for fermentation, is a complex process typically involving chemical and enzymatic steps. In this study, we developed a method to quickly analyze residual sugar-containing oligomers to determine the structural features that are resistant to chemical and enzymatic treatments. Several different structural features were identified that, in future studies, will be targeted by additional enzymes that specifically break these bonds to release free sugars and presumably will increase ethanol yields. This work represents analytical method development for the identification of recalcitrant bonds and an approach to quickly monitor additional fermentation experiments to identify specific enzymes to hydrolyze these bonds. The use of this method and the information gained from its application will be of value to plant breeders interested in developing new energy crops with more desirable compositions and enzyme companies developing products for improved conversion of biomass to fuels and chemicals.

Technical Abstract: Switchgrass is a potential source of renewable biomass for conversion to liquid biofuels. Efficient conversion requires effective strategies for pretreatment and enzymatic saccharification to produce fermentable sugars. Standard analysis of fermentation liquids includes detection of monosaccharides and ethanol to determine efficiency of conversion. Larger components, specifically oligosaccharides, are typically not measured due to the structural complexity of the products; however, as oligosaccharides they represent carbon available in biomass that is not converted to liquid fuels. In this study, ammonia-pretreated switchgrass was enzymatically depolymerized either independently or under simultaneous saccharification and fermentation conditions. Residual oligosaccharides were reducing end labeled followed by hydrophilic interaction liquid chromatography mass spectrometry/mass spectrometry analysis. These data reveal 20 oligosaccharide peaks with distinct retention times and tandem mass spectrometry fragmentation patterns representing 13 different oligosaccharide compositions. All measured compositions were smaller than a chain length of six and were neither linear xylooligosaccharides nor modified with phenolic esters.