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Cereal Chem 72:411-418  |  VIEW ARTICLE

Physicochemical and Functional Properties of Rye Nonstarch Polysaccharides. VI. Variability in the Structure of Water- Unextractable Arabinoxylans.

C. J. A. Vinkx, I. Stevens, H. Gruppen, P. J. Grobet, and J. A. Delcour. Copyright 1995 by the American Association of Cereal Chemists, Inc. 

A fraction rich in water-unextractable arabinoxylans was isolated from rye wholemeal. Arabinoxylans were solubilized by a sequence of alkaline extractions. Structural features of these arabinoxylans were investigated by methylation analysis and nuclear magnetic resonance spectroscopy. Three groups of water- unextractable arabinoxylans could be recognized, differing in extractability, solubility, and structure. The first group had an intermediate arabinose-to-xylose ratio (A/X) of 0.55-0.79 and was extractable either with saturated Ba(OH)2 containing 1% NaBH4 or with water after saturated Ba(OH)2 extraction. The polymers were soluble in water after neutralization of the alkaline extract, but they precipitated in saturated ammonium sulfate solution. They contained terminal arabinose residues and unsubstituted, 3-mono-, 2- mono-, and disubstituted xylose residues. A second group had an A/X of approximately 1.1 and was partly extracted with alkali; more could be extracted after delignification. This group was soluble in water and in saturated ammonium sulfate solution. Typical structural features in this arabinoxylan were: substituted arabinose residues (40% of arabinoses), terminal xylose residues (26% of xyloses), and terminal galactose residues. A third group of arabinoxylans was extractable with 1M KOH, had low water solubility after neutralization of the alkaline extract, and had an A/X of approximately 0.2. Besides arabinoxylan, beta- glucan was present in large proportions in rye cell-wall material. Glucomannan and xyloglucan were also detected.

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