Paul Menut

Reactivity of wheat gluten protein during mechanical mixing: radical and nucleophilic reactions for the addition of molecules on sulfur.

Mechanical properties of gluten-based biomaterials, such as break stress, were known to be influenced by temperature and shear stresses applied during processing. It is well documented in literature that these processing parameters promoted wheat gluten protein aggregation. Exchange between disulfide bonds and thiol groups oxidation are the postulated mechanisms that lead to gluten protein solubility loss in sodium dodecyl sulfate buffers. Both nucleophilic and radical reactions were postulated to act during gluten aggregation. To graft molecules on gluten, a study was carried out to explore the reactivity of its thiol and disulfide groups during thermomechanical mixing. A range of reactants able to react via radical or nucleophilic pathways with thiol groups were synthesized. Reactivity between gluten and functions was quantified by gluten solubility measurements. This investigation and literature observations allowed proposal of a general gluten aggregation mechanism during mixing.

Interactions of Kraft lignin and wheat gluten during biomaterial processing: evidence for the role of phenolic groups.

The chemical interactions between Kraft lignin and wheat gluten under processing conditions were investigated by determining the extent of the protein network formation. To clarify the role of different chemical functions found in lignin, the effect of Kraft lignin was compared with that of an esterified lignin, in which hydroxyl groups had been suppressed by esterification, and with a series of simple aromatics and phenolic structures with different functionalities (conjugated double bonds, hydroxyl, carboxylic acid, and aldehyde). The protein solubility was determined by using the Kjeldahl method. The role of the hydroxyl function was assessed by the significantly lower effect of esterified lignin. The importance of the phenolic radical scavenging structure is evidenced by the effect of guaiacol, which results in a behavior similar to that of the Kraft lignin. In addition, the significant effect of conjugated double bonds on gluten reactivity, through nucleophilic addition, was demonstrated.

Structure formation of poly (ether-imide) films using non-solvent vapor induced phase separation: relationship between mass transfer and relative humidity

Structure formation of poly(ether-imide) films using vapor induced phase separation was studied in relation with the elaboration process. Dense and cellular structure can be obtained depending on the processing parameters. When the solvent evaporation took place under humidified air, kinetic data from gravimetric measurements showed that the overall mass of the film was first increasing before decreasing to a plateau. An analysis in terms of drying rate revealed that mass transfers were occurring as if there was a thin layer of volatile molecule at the top of the forming film. Solvent and non-solvent transfers were demonstrated to be closely dependent on the relative humidity.

Modification of the wheat gluten network by Kraft lignin addition.

The effect of Kraft lignin (KL) on wheat gluten (WG) network formation during biomaterial processing was investigated. Gluten plasticized with glycerol was blended with a variable content of KL and processed into material by mixing and hot molding. The effect of KL on WG cross-linking was assessed by size-exclusion chromatography coupled with specific detection of KL by fluorescence. Whereas processing of WG usually results in cross-linking and solubility loss, KL addition promoted an increase of gluten protein solubility in sodium dodecyl sulfate buffers. The feature demonstrates that KL functional groups hinder WG aggregation. A radical scavenger activity of KL toward the thiyl radicals produced during gluten mixing is proposed. Mixing also promotes the association of KL with WG as evidenced by the coelution of KL and WG in size exclusion high-performance liquid chromatography. Finally, gluten aggregation and cross-linking can be obtained by immersion of the materials in a dioxane-water solution, thereby demonstrating the occurrence of stabilized radicals on WG material mixed with KL.

Poly(ether imide) membrane formation by water vapour induced phase inversion

The film formation by the phase inversion process induced by humidified air was investigated at 40°C from a 16 wt-% poly(ether imide)/N-methyl-2-pyrrolidinone solution. Weight measurements of the film forming system and video recording of the phase separation were performed in-situ to get a deep insight of the mass transfer and of the mechanism of the structure formation. Films with a cellular morphology were produced for a processing relative humidity higher than 30% and dense homogeneous films below this value. The influence of the relative humidity on the film morphology (dense or cellular, cell size, anisotropy) was discussed in terms of thermodynamic (ternary phase diagram) and kinetic aspects of the phase separation. On this basis, we propose a phenomenological model to explain what happens during the film formation.

Osmotic Compression of Anisotropic Proteins: Interaction Properties and Associated Structures in Wheat Gliadin Dispersions

In this Article, we investigated the interaction properties of wheat gliadins, properties that are at the basis of their functionality in wheat grain and in food matrixes. We established the equation of state of our isolate by osmotic compression and characterized the concentration-induced structural transitions, from the secondary structure of proteins to the rheological properties. We evidenced three thermodynamical regimes corresponding to several structuring regimes. First, for Φ < 0.03, gliadins behave as repulsive colloids, with a positive second virial coefficient, arising presumably from their surface charge density and/or their steric repulsion. No intermolecular interaction was detected by FT-IR, suggesting that proteins form a stable dispersion. In the second regime, the system becomes more easily compressible, i.e., less repulsive and/or more attractive. It is associated with the disappearance of β-sheet intramolecular structures of the proteins in favor of random coils/α-helix and intermolecular β-sheet interactions. This coincides with the appearance of elasticity and the increase of the apparent viscosity. Finally, in the last regime, for Φ > 0.16, FT-IR spectra show that proteins are strongly interacting via intermolecular interactions. A correlation peak develops in SAXS, revealing a global order in the dispersion. Interestingly, the osmotic pressure applied to extract the solvent is higher than expected from a hard-sphere-like protein and we highlighted a liquid-like state at very high concentration (>450 g L(-1)) which is in contrast with most proteins that form gel or glass at such concentration. In the discussion, we questioned the existence of supramolecular assemblies and the role of the solvation that would lead to this specific behavior.

Valorization of industrial by-products through bioplastic production: defatted rice bran and kraft lignin utilization

Abstract The objective of this study was to develop a bioplastic from industrial by-products. Commercial defatted rice bran (DRB) was extruded with 0–30% kraft lignin (KL) as a filler and 30% glycerol as a plasticizer. Firstly, the effect of extrusion temperature on the plasticized DRB’s processability was determined. Increasing the die extrusion temperature from 100°C to 150°C improved the extrudability by decreasing the die pressure and motor current. Subsequently, the effect of KL on plasticized DRB was studied. The addition of 10–30% KL improved DRB processability. The addition of 30% KL markedly lowered the die pressure in comparison to using a 150°C extrusion temperature. Moreover, KL addition decreased DRB viscosity determined by a capillary rheometer. These results were coherent with a decreased storage modulus in a rubber state and an increased tan δ height determined by a dynamic mechanical thermal analyzer (DMA). However, n values of DRB with 10–30% KL could not be explained by a simple mixing rule. This may be attributed to the interaction between DRB and KL, as shown by Fourier transform infrared (FTIR) spectra. KL addition increased Young’s modulus and the glass transition temperature (Tg) of plasticized DRB. Therefore, blending DRB with KL is an effective way to improve polymer flowability at the processing temperature and mechanical properties at ambient temperature.

Dynamics of liquid-liquid phase separation of wheat gliadins

During wheat seeds development, storage proteins are synthetized and subsequently form dense protein phases, also called Protein Bodies (PBs). The mechanisms of PBs formation and the supramolecular assembly of storage proteins in PBs remain unclear. In particular, there is an apparent contradiction between the low solubility in water of storage proteins and their high local dynamics in dense PBs. Here, we probe the interplay between short-range attraction and long-range repulsion of a wheat gliadin isolate by investigating the dynamics of liquid-liquid phase separation after temperature quench. We do so using time-resolved small angle light scattering, phase contrast microscopy and rheology. We show that gliadins undergo liquid-liquid phase separation through Nucleation and Growth or Spinodal Decomposition depending on the quench depth. They assemble into dense phases but remain in a liquid-like state over an extended range of temperatures and concentrations. The analysis of phase separation kinetics reveals that the attraction strength of gliadins is in the same order of magnitude as other proteins. We discuss the respective role of competing interactions, protein intrinsic disorder, hydration and polydispersity in promoting local dynamics and providing this liquid-like behavior despite attractive forces.