Résumé:

The origin of the unique rheological properties of gluten, the water-insoluble protein fraction of wheat, is crucial in bread-making processes and questions scientists since decades. Gluten is a complex mixture of monomeric and polymeric proteins. To better understand the supramolecular structure of gluten and its link to the material properties, we develop and characterize model gluten using a combination of rheology, biochemistry and scattering techniques. In this framework, we investigate the linear and non-linear viscoelastic properties of samples produced by the dispersion of gluten proteins in a solvent. We vary the quality of the solvent (various water/ethanol mixtures), the protein concentration, and the protein composition, which we finely control thanks to a novel protocol based on a liquid-liquid phase separation. We show that the complex viscoelasticity of the gels exhibits concentration/aging time/solvent composition superposition principles, demonstrating the self-similarity of the gels produced in different conditions. All gels can be regarded as near critical gels with characteristic rheological parameters, elastic plateau, and characteristic relaxation time, which are related to one another, as a consequence of self-similarity, and span several orders of magnitude when changing the parameters. Structural features probed by X-ray, neutron and light scattering experiments provide a quantitatively consistent physical picture and of near-criticality and provide crucial molecular clues of the role of intramolecular H-bonds in the gelation process. Non-linear rheology, as probed by shear start-up experiments, is also intimately related to the sample structural features.