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Isolation and characterization of unhydrolyzed oligosaccharides from switchgrass (Panicum virgatum, L.) xylan after exhaustive enzymatic treatment with commercial enzymen preparations

Michael J. Bowman, Bruce S. Dien, Karl E. Vermillion, Jeffrey A. Mertens
Carbohydrate research 2015 v.407 pp. 42-50
Panicum virgatum, alpha-N-arabinofuranosidase, biofuels, cell walls, enzymatic hydrolysis, enzymatic treatment, hydrolysis, nuclear magnetic resonance spectroscopy, oligosaccharides, xylan
Switchgrass (Panicum virgatum, L.) is a potential renewable source of carbohydrates for use in microbial conversion to biofuels. Xylan comprises approximately 30% of the switchgrass cell wall. To understand the limitations of commercial enzyme mixtures, alkali-extracted, isolated switchgrass xylan was hydrolyzed by the action of two commercial enzyme cocktails, in the presence and absence of an additional alpha-arabinofuranosidase enzyme. The two most abundant enzymatic digestion products from each commercial enzyme treatment were separated and characterized by LC-MSn, linkage analysis, and NMR. The most abundant oligosaccharide from each commercial cocktail was susceptible to hydrolysis when supplemented with a GH62 alphaarabinofuranosidase enzyme; further characterization confirmed the presence of (1->3)-alphaarabinose linkages. These results demonstrate the lack of the required selectivity for arabinose-containing substrates in the commercial enzyme preparations tested. One product from each condition remained intact and was found to contain (1->2)-beta-xylose-(1->3)-alphaarabinose side chains; this linkage acts as a source of oligosaccharide recalcitrance.