Compositional Analysis of Water-Soluble Materials in Switchgrass

Any valuation of a potential feedstock for bioprocessing is inherently dependent upon detailed knowledge of its chemical composition. Accepted analytical procedures for compositional analysis of biomass water-soluble extracts currently enable near-quantitative mass closure on a dry weight basis. Techniques developed in conjunction with a previous analytical assessment of corn stover have been applied to assess the composition of water-soluble materials in four representative switchgrass samples. To date, analytical characterization of water-soluble material in switchgrass has resulted in >78% mass closures for all four switchgrass samples, three of which have a mass closure of >85%. Over 30 previously unknown constituents in aqueous extracts of switchgrass were identified and quantified using a variety of chromatographic techniques. Carbohydrates (primarily sucrose, glucose, and fructose) were found to be the predominant water-soluble components of switchgrass, accounting for 18−27% of the dry weight of extractives. Total glycans (monomeric and oligomeric sugars) contributed 25−32% to the dry weight of extractives. Additional constituents contributing to the mass balance for extractives included various alditols (2−3%), organic acids (10−13%), inorganic ions (11−13%), and a distribution of oligomers presumed to represent a diverse mixture of lignin−carbohydrate complexes (30−35%). Switchgrass results are compared with previous analyses of corn stover extracts and presented in the context of their potential impact on biomass processing, feedstock storage, and future analyses of feedstock composition.