Physicochemical and functional properties of rye nonstarch polysaccharides. V. Variability in the structure of water-soluble arabinoxylans

Subsequent increases in the degree of ammonium sulfate saturation of a rye water extract allowed the precipitation of at least three distinct arabinoxylan fractions that differed markedly in molecular weight distribution and fine structure. A first (main) fraction, precipitated between 25 and 50% saturation, had an arabinose-to-xylose ratio (A/X) of 0.5 with virtually all branched xylose residues substituted at 0-3 with arabinose (as shown by 500 Mhz 1H-nuclear magnetic resonance [NMR]). This fraction contained ferulic acid (0.04-0.07%), had a lower molecular weight than the other fractions, and gelled oxidatively with the hydrogen peroxide-peroxidase system. A second (small) fraction had an A/X of 1.4 and precipitated between 75 and 100% ammonium sulfate saturation. It did not gel. All branched xylose residues were substituted at both O-2 and O-3 with arabinose. Structures of one, two, and more consecutive, disubstituted xylose residues in the xylan chain could be recognized in the 1H-NMR spectra. Fractions precipitating between 50 and 75% ammonium sulfate saturation were not mixtures of these two arabinoxylan fractions because the 1H-NMR spectra showed differences in the ratio of isolated to paired disubstituted xylose residues