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Abstract: In order to utilize hemicelluloses from biomass as a feedstock for production of higher value added products such as biofuels and bio-based chemicals, it is essential to assess the chemical composition of the liquid phase and molecular weight distribution of isolated carbohydrates. The association of hemicelluloses with lignin also plays an important role for utilization of isolated hemicelluloses. In the present study carbohydrates were first extracted from a mixture of southern hardwoods by autohydrolysis at different temperatures for 100min, and then precipitated after mixing with four volumes of ethanol. Depending on the temperature, all (100% at 130°C) or a small part (5% at 170°C) of the oligomeric hemicelluloses present in the extract precipitated together with some lignin and oligo-glucose (glucans). The classical iodine test confirmed that most of the glucans are actually starch. Oligo-glucose is the major component in the precipitate from extracts produced at 150°C and below, while xylan is the main component at 160°C. Almost all lignin in the precipitate is in the form of lignin–carbohydrate complexes. The average M w of the carbohydrates isolated from the extract decreases with increasing autohydrolysis temperature. The average DP of hemicelluloses isolated from the extract decreases from about 71 to 36 over the temperature range from 130 to 170°C during 100min autohydrolysis. [ABSTRACT FROM AUTHOR]

Abstract: The carbohydrate composition of lignocellulosic biomass is normally obtained by the quantification of monomers after two stages of hydrolysis in H2SO4. A new two-stage hydrolysis protocol has recently been developed but so far only results for temperate hardwoods have been reported. In this investigation the new protocol was used in the analysis of depithed sugarcane bagasse, Eucalyptus grandis and bamboo. The results were compared to those from the traditional hydrolysis protocol. Sugar monomers were quantified by 1H NMR and high performance liquid chromatography (HPLC) and there were no significant differences between the two techniques. The new and traditional hydrolysis protocols gave nearly identical results for the bagasse and bamboo samples both of which contain <0.10 uronic acids per xylose unit. However, the new protocol gave a higher xylan yield (13.2% vs. 12.1%) for the E. grandis that contained >0.20 uronic acids per xylose units. For both hydrolysis protocols, summative analyses in the range of 97.5–101.0% were obtained for the three biomass samples. However, the range was narrower (98.6–99.5%) for the new hydrolysis protocol coupled with 1H NMR analysis. [Copyright &y& Elsevier]