Tuesday, May 3, 2011
Switchgrass (SG) is a potential renewable biomass source for conversion to liquid biofuels. Efficient conversion requires effective strategies for pretreatment and enzymatic saccharification to fermentable sugars. Standard analysis of fermentation broth includes detection of monosaccharides and ethanol (or other products) to determine efficiency of conversion. However, larger components, specifically oligosaccharides, are typically not measured due to analytical limitations. Further analysis of residual material from pretreated biomass subjected to enzymatic depolymerization will reveal oligosaccharide sequences that are resistant to hydrolysis. Therefore, ammonia-pretreated SG was enzymatically depolymerized for 72 hours by the action of a combination of industrial enzymes. Simultaneous saccharification and fermentation (SSF) of pretreated SG should mitigate product inhibition of the enzyme cocktail. Therefore, pretreated SG was treated by SSF using the same enzymes and fermented to ethanol using Saccharomyces cerevisiae. Residual oligosaccharides were analyzed by liquid chromatography mass spectrometry (LC-MS/MS) as it is a useful tool for analyzing oligosaccharides by combining high sensitivity with the ability to determine oligosaccharide composition and, potentially, structural information via the fragmentation patterns of analytes. Prior to analysis by LC-MS, a reducing-end label was incorporated into mono- and oligo-saccharides by reductive amination to facilitate identification of reducing sugar components. The incorporated label provides a traceable chromophore and differentiates the reducing and non-reducing end derived fragments generated by tandem mass spectrometric analysis.