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

Cereal Chem. 72(4):41 1-418 A fraction rich in water-unextractable arabinoxylans was isolated from nose residues and unsubstituted, 3-mono-, 2-mono-, and disubstituted rye wholemeal. Arabinoxylans were solubilized by a sequence of alkaline xylose residues. A second group had an A/X of -1.1 and was partly extractions. Structural features of these arabinoxylans were investigated extracted with alkali; more could be extracted after delignification. This by methylation analysis and nuclear magnetic resonance spectroscopy. group was soluble in water and in saturated ammonium sulfate solution. Three groups of water-unextractable arabinoxylans could be recognized, Typical structural features in this arabinoxylan were: substituted arabinose differing in extractability, solubility, and structure. The first group had residues (40% of arabinoses), terminal xylose residues (26% of xyloses), an intermediate arabinose-to-xylose ratio (A/X) of 0.55-0.79 and was and terminal galactose residues. A third group of arabinoxylans was exextractable either with saturated Ba(OH) 2 containing 1% NaBH4 or with tractable with IM KOH, had low water solubility after neutralization water after saturated Ba(OH) 2 extraction. The polymers were soluble in of the alkaline extract, and had an A/X of -0.2. Besides arabinoxylan, water after neutralization of the alkaline extract, but they precipitated 13-glucan was present in large proportions in rye cell-wall material. Glucoin saturated ammonium sulfate solution. They contained terminal arabi- mannan and xyloglucan were also detected.