  The supramolecular organization of wheat gluten proteins is largely unknown
due to the intrinsic complexity of this family of proteins and their
insolubility in water. We fractionate gluten in a water/ethanol (50/50 v/v) and
obtain a protein extract which is depleted in gliadin, the monomeric part of
wheat gluten proteins, and enriched in glutenin, the polymeric part of wheat
gluten proteins. We investigate the structure of the proteins in the solvent
used for extraction over a wide range of concentration, by combining X-ray
scattering and multi-angle static and dynamic light scattering. Our data show
that, in the ethanol/water mixture, the proteins display features
characteristic of flexible polymer chains in a good solvent. In the dilute
regime, the protein form very loose structures of characteristic size 150 nm,
with an internal dynamics which is quantitatively similar to that of branched
polymer coils. In more concentrated regimes, data highlight a hierarchical
structure with one characteristic length scale of the order of a few nm, which
displays the scaling with concentration expected for a semi-dilute polymer in
good solvent, and a fractal arrangement at much larger length scale. This
structure is strikingly similar to that of polymeric gels, thus providing some
factual knowledge to rationalize the viscoelastic properties of wheat gluten
proteins and their assemblies.
