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Isolation and characterization of unhydrolyzed oligosaccharides from switchgrass (Panicum virgatum, L.) xylan after exhaustive enzymatic treatment with commercial enzymen preparations
- Bowman, Michael J., Dien, Bruce S., Vermillion, Karl E., Mertens, Jeffrey A.
- 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.