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Cereal Chem. 70:209-214   |  VIEW ARTICLE

Purification and Characterization of Two Arabinoxylans from Wheat Bran.

K. Shiiba, H. Yamada, H. Hara, K. Okada, and S. Nagao. Copyright 1993 by the American Association of Cereal Chemists, Inc. 

Water-soluble hemicellulose (WSH) was extracted and purified from wheat bran. The yield of WSH was 7.6% of the bran. WSH was mainly comprised of arabinoxylan (86.4%). Two major arabinoxylans of the WSH were fractionated by a diethylaminoethyl (DEAE)-Sepharose CL-6B column. One of them (AX-1) passed through the DEAE-Sepharose column, but the other (AX-2) was adsorbed on the column and was eluted with a linear gradient of 0.1-0.3M NaCl. These fractions were further purified by Sephacryl S-200. The carbohydrate yields of AX-1 and AX-2 were around 40 and 60% of the WSH, respectively. AX-1 was comprised principally of xylose (50.4%), arabinose (28.7%), and glucose (17.3%), whereas AX-2 contained some uronic acid (4.7%) and proteinaceous materials (4.8%) as well as xylose (42.4%) and arabinose (45.5%); little glucose (2.4%) was found in AX-2. Size-exclusion high-performance liquid chromatography of AX-1 and AX-2 showed that they had almost the same peaks in the symmetric molecular mass distribution that corresponded to a molecular mass of around 300,000-350,000 Da of pullulan. Enzymatic hydrolysis of the polysaccharides contained in AX-1, catalyzed by endo-1,4-beta-D-xylanase, reduced the molecular weight of the fragments to less than 10,000 Da. However, polysaccharides o f AX-2 did not show any change in molecular weight distribution. Methylation analysis suggested that AX-2 had a more branched structure than AX-1, becuse AX-2 had a lower ratio (1/1.88) of 2,3-dimethylxylose to 2- or 3- methylxylose than did AX-1 (1/0.59). It also showed that AX-1 was constituted of 37% unsubstituted, 22% single-substituted, and 40% double-substituted xylopyranosyl residues, whereas the percentages for AX-2 were 21, 39, and 40%, respectively.

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