New features of plant-fructan structure revealed by methylation analysis and carbon-13 n.m.r. spectroscopy

Abstract

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 13C 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 β- 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.