Abstract
Successive extraction of rice hull with hot water, 0.5% ammonium oxalate, 4% potassium hydroxide, and 24% potassium hydroxide, followed by neutralization of the alkaline extracts, yielded seven polysaccharide fractions. An electrophoretically homogeneous arabinoxylan was obtained as a precipitate (HC-IA) after neutralization of the 4% potassium hydroxide extract. The homogeneity of the rice-hull arabinoxylan was confirmed by ultracentrifugation, and by gel filtration through Sepharose CL-6B. It contained a small proportion of uronic acid (1.5%) and, on complete hydrolysis with acid, gave xylose and arabinose in the ratio of ∼19:1. This value is in close agreement with those calculated from the results of methylation analysis, and fragmentation analysis with endo-(1→4)-β- d-xylanase. The results from the methylation analysis, and from fragmentation analyses with acid and with endo-(1→4)-β- d-xylanase, indicated that the repeating unit of this arabinoxylan consists of a linear chain of 19 (1→4)-linked, β- d-xylosyl residues and an arabinofuranosyl side-chain joined through a (1→3) linkage.
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