Polymeric Assembly of Gluten Proteins in an Aqueous Ethanol Solvent

TL;DR

This study reveals that gluten proteins in an aqueous ethanol solvent form hierarchical, polymer-like structures, providing insights into their viscoelastic properties and supramolecular organization.

Contribution

It demonstrates that gluten proteins behave as flexible polymers in ethanol/water, with hierarchical structures similar to polymer gels, advancing understanding of their assembly.

Findings

Proteins display features of flexible polymer chains in ethanol/water.

Loosely structured proteins of about 150 nm in dilute solutions.

Hierarchical, fractal structures consistent with semi-dilute polymers.

Abstract

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.