NEW FEATURES OF PLANT-FRUCTAN STRUCTURE REVEALED BY METHYLATION ANALYSIS AND C-13 NMR-SPECTROSCOPY

The chemical structures of inulins, levans, highly branched fructans, and fructan oligomers from plants were determined by gas-liquid chromatography of partially methylated alditol acetates and C-13 nuclear magnetic resonance spectroscopy of the native polymers. Results obtained by these sensitive techniques revealed that these polymers contained small proportions of linkages atypical of the expected structures; inulins were composed of primarily (2 --> 1)-linked beta-D-fructofuranosyl units, but contained measurable amounts of (2 --> 1,2 --> 6)-linked branch point residues and (2 --> 6)-linked fructosyl units, and the levans possessed atypical (2 --> 1)-linked fructofuranosyl and branch-point residues. The highly branched wheat fructans were particularly dynamic, exhibiting enrichment of (2 --> 1)-linkages during early induction of synthesis but enrichment of (2 --> 6) linkages upon extended periods of fructan accumulation. The techniques used here should prove valuable in determining the biological significance of these variations in structure.