Compositional Analysis of Water-Soluble Materials in Corn Stover

Department of Chemistry & Biochemistry, Baylor University, One Bear Place, Box 97348, Waco, Texas 76798, USA.
Journal of Agricultural and Food Chemistry (Impact Factor: 2.91). 08/2007; 55(15):5912-8. DOI: 10.1021/jf0700327
Source: PubMed


Corn stover is one of the leading feedstock candidates for commodity-scale biomass-to-ethanol processing. The composition of water-soluble materials in corn stover has been determined with greater than 90% mass closure in four of five representative samples. The mass percentage of water-soluble materials in tested stover samples varied from 14 to 27% on a dry weight basis. Over 30 previously unknown constituents of aqueous extracts were identified and quantified using a variety of chromatographic techniques. Monomeric sugars (primarily glucose and fructose) were found to be the predominant water-soluble components of corn stover, accounting for 30-46% of the dry weight of extractives (4-12% of the dry weight of feedstocks). Additional constituents contributing to the mass balance for extractives included various alditols (3-7%), aliphatic acids (7-21%), inorganic ions (10-18%), oligomeric sugars (4-12%), and a distribution of oligomers tentatively identified as being derived from phenolic glycosides (10-18%).

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    • "Hemicellulose solubilized at higher severity (log R 0 = 4.42), gave a mixture of xylose monomers (7.6 g/L) and xylo-oligomers (6.5 g/L); or predominately oligomers (12.5 g/L) at the lower severity (log R 0 = 3.83) (comparison inTable 1). Phenolic compounds, derived from lignin degradation and from phenolic ester groups associated with hemicellulose (Chen et al., 2007) inhibit enzymatic hydrolysis (Ximenes et al., 2010Ximenes et al., , 2011). The highest concentration of phenolics (2.42 g/L) corresponded to the highest severity (log R 0 = 4.42). "
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    ABSTRACT: This work shows both cellulases and hemicellulases are inhibited and deactivated by water-soluble and acetone extracted phenolics from sugarcane bagasse pretreated at 10% (w/v) for 30min in liquid hot water at 180 or 200°C. The dissolved phenolics in vacuum filtrate increased from 1.4 to 2.4g/L as temperature increased from 180 to 200°C. The suppression of cellulose and hemicellulose hydrolysis by phenolics is dominated by deactivation of the β-glucosidase or β-xylosidase components of cellulase and hemicellulase enzyme by acetone extract at 0.2-0.65mgphenolics/mg enzyme protein and deactivation of cellulases and hemicellulases by the water soluble components in vacuum filtrate at 0.05-2mg/mg. Inhibition was a function of the type of enzyme and the manner in which the phenolics were extracted from the bagasse.
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    • "Wood chips had the highest holocellulose content (43.1%, cellulose and hemicellulose combined); while lawn grass had the highest extractives content (30.5%, water and ethanol solutes combined) and crude protein content (8.8%). Extractives include compounds such as free sugars, oligosaccharides, and organic acids (Chen et al., 2007), which are easily degradable for biogas generation (Liew et al., 2012). Leaves had the highest lignin content (36.1%). "
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    • "The increase of severity had only a minor effect on glucan solubilisation, with a maximum glucan loss of 9.9% for the severest condition. Glucan solubilisation that occurred for the less severe conditions (for instance 6.0% at severity 1.63) may be related with loss of water soluble non-structural sugars and not to cellulose hydrolysis (Chen et al., 2007). Low solubilisation of glucan has also been reported for corn cobs autohydrolysis (Garrote et al., 2001; Moura et al., 2007) and is an advantage for the integral utilisation of this raw material in a biorefinery framework. "
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    ABSTRACT: Corn straw was chemically and anatomically characterised. Hydrothermal processing (autohydrolysis) was used for the selective solubilisation of hemicelluloses. The raw material was treated under non-isothermal conditions (150-240 degrees C) and the effects on the composition of both liquid and solid phases were evaluated. The yields and composition of the solid fraction and soluble products are presented and interpreted using the severity factor (log R-0). The operational conditions for the maximum yield of xylo-oligosaccharides (XOS) of 53% of initial xylan, were established for log R-0 of 3.75. Under these conditions 72% of xylan was hydrolysed while cellulose and lignin were not substantially affected although an increase in the enzymatic digestibility of cellulose was attained. For the severest condition (log R-0 =4.51) the solids contained 61.7% glucan and 31.0% lignin. The XOS rich liquors and the glucan and lignin enrichment of the solid phase make corn straw a suitable raw material in a biorefinery framework and the hydrothermal treatment a favourable first step in the processing.
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