PhD Proposal, University of Montpellier 2 (France), Biopolymer Soft Matter

Name of the Laboratory : UMR 1208 Ingénierie des Agro-polymères et Technologies Emergentes (IATE), 2, place Pierre Viala, 34060 Montpellier cedex 1, FRANCE
PhD. director : Pr. Christian Sanchez (UM2), (PhD co-director: Paul Menut, MCF Montpellier SupAgro)
1-PH.D subject
Title: Soft matter based on biopolymers: solid-liquid transition of gluten, a viscoelastic protein material
Key-words: condensed phase, jamming, SAXS, USAXS, confocal microscopy, FRAP, proteins, solvatation, diffusion, fluorescence, rheology
1. Scientific context and objectives
The composition and structure of gluten from wheat kernel are key parameters governing its viscoelastic properties. The latter allow to process the gluten as materials, such as food and biomaterial matrices. Gluten proteins are to the origin of cohesion, viscoelastic, extensibility/fracture and permeability properties of these materials, especially their resistance to hydration. Gluten proteins can be divided in two major fractions according to their solubility in polar solvents: soluble monomeric gliadins and partly soluble polymeric glutenins. The total amount and size distribution of the polymeric protein fraction have been mainly times correlated to the mechanical properties of materials (bread, pasta, biomaterials).
The structure of supramolecular assemblies between gliadins and glutenins is a subject of discussions and controversy. Like any self-assembled macromolecular system, the thermodynamic equilibrium is based on the balance between, on the one part gliadins-glutenins interactions, on the other hand on their interactions with the solvent. On the caoutchoutic domain of gluten, the effect of hydration on its structure and functionality have never been explored. However, the water content of gluten in this domain allows to consider it like a soft condensed material, stopped or fluid (jamming transition). The determination of a phase diagram in this range of water content is then fundamental in order to control the building of matrices with controlled mechanical or nutritional properties.
The main scientific objective of this project is to establish the relationships between the structure, mechanical properties and diffusional properties of gluten. More specifically, we will determine the influence of gluten protein hydration state on their organisation from the supramolecular to the macroscopic scale, on their rheological properties and on the mobility of colloidal fluorescent probes in the matrix. The study will allow us to establish the conditions leading to the dynamical arrest of the system (protein composition, hydratation state, spatial variation of the correlation length).
2. Methodologies and program
Methodologies:
Different protein systems (variable gliadins/glutenins ratios) will be set to thermodynamic equilibrium at different hydratation levels applying external osmotic pressures, through dialysis against synthetic polymer solutions. The structure of the different systems will be determined using spectroscopic methods such as SAXS and USAXS. The compacity of systems will be indirectly evaluated by confocal microscopy (FRAP method; measurement of diffusion rates of fluorescent probes with known hydrodynamic radius). The obtained data will be compared to direct measurements of interstitial volumes by granulo-polarimetry, which principle is based on the analysis of incoherent transport of polarized light. The functionality of systems will be determined by creep and oscillation rheological measurements.
Program:
Each stage of the program will be preceded by a specific bibliography.
- months 0-12: The Ph.D. student will determine the phase diagrams osmotic pressure-water content of different gliadins/glutenins mixtures, depending on the physico-chemical environment (ionic strength, pH). In parallel, rheological propertie of the different systems will be studied.
- months 13-15: Paper writing on the data obtained
- months 15-19: Development and validation of the confocal microscopic method in FRAP mode, including the search of fluorescent probes, with appropriate sizes, stability and quantic yield, the adjustment of microscope in terms of resolution, signal/noise ratio and gain, as well as image analysis.
- months 20-32: The previous method will be used on the same systems than those studied during the first Ph.D year. Granulo-polarimetric measurements will be carried out. In parallel, the structure of systems will be studied using SAXS and USAXS.
- months 32-36 mois: Ph.D and papers writing
Contact: Pr. C. Sanchez, tel: +33 4 99 61 20 85, mail: Christian.Sanchez@supagro.inra.fr; UMR Ingénierie des Agro-Polymères et Technologies Emergentes (IATE), 2, place Pierre Viala, 34060 Montpellier cedex 1, France.