Fractional and structural characterization of hemicelluloses isolated by alkali and alkaline peroxide from barley straw |
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Authors: | R. C. Sun X. F. Sun |
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Affiliation: | a State Key Laboratory of Pulp and Paper Engineering, College of Paper and Environment Engineering, South China University of Technology, Guangzhou, People's Republic of China b Centre for Straw and Wood Utilization, The North-Western Sciences and Technology University of Agriculture and Forestry, Yangling, People's Republic of China |
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Abstract: | Eight hemicellulosic fractions were obtained by sequential treatment of dewaxed barley straw with 0.1 M NaOH at 45 °C for 3 h, 0.25, 0.5, 1.0, 1.5, 2.0, and 3.0% H2O2 at 45 °C for 3 h at pH 11.5, and 10% KOH–1% Na2B4O7·10H2O at 28 °C for 15 h under continuous agitation. The yields of the fractions were 8.0, 3.1, 3.3, 3.3, 2.2, 2.0, 2.0, and 9.9%, respectively, of the initial amount of barley straw, corresponding to the dissolution of 21.6, 8.4, 8.9, 8.9, 5.9, 5.4, 5.4, and 26.7% of the original hemicelluloses. Meanwhile, the successive treatment also solubilized 29.1, 15.8, 14.6, 10.8, 4.5, 3.2, 2.7, and 3.7% of the original lignin, respectively. This sequential extraction together resulted in dissolution of 91.1% of the original hemicelluloses and 84.8% of the original lignin. The 0.1 M NaOH-soluble hemicellulosic fraction contained mainly xylose, glucose, and arabinose, 44.2, 15.7, and 15.2%, respectively, while the 10% KOH–1% Na2B4O7·10H2O-soluble fraction predominated in xylose, 75.0%. The six alkaline peroxide-soluble fractions were composed of 50.3–54.4% xylose, 14.7–16.9% arabinose, 6.8–10.7% glucose, 6.8–8.5% glucuronic acid or 4-O-methyl--glucuronic acid, 0.4–1.5% mannose, and 0.3–1.2% rhamnose. All the hemicellulosic fractions contained substantial amounts of glucuronoarabinoxylans and noticeable quantities of β-glucans. In comparison, the six hemicellulosic fractions, isolated with alkaline peroxide, had much higher molecular weights (56,890–63,810 g mol−1) than those of the two hemicellulosic preparations (28,000–29,080 g mol−1), isolated with alkali in the absence of hydrogen peroxide. The thermal stability of the hemicelluloses increased with an increment of their molar mass. |
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Keywords: | Barley straw Hemicelluloses Alkali Alkaline peroxide Sugars Lignin |
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