With the demography growth, there is a huge pressure on protein demand, and the development of plant based proteins is required for a future sustainable food production. Plant proteins are efficient to stabilize interfaces in foams or emulsions, and the understanding of physical mechanisms at the origin of their interfacial behavior is important to develop new products. We investigate the adsorption of wheat grains (gliadin) and sunflower seeds (helianthinin) proteins, at air-water and oil-water interfaces, respectively. A combination of tensiometry, dilatational viscoelasticity and ellipsometry measurements is used to determine the adsorption mechanisms, and characterize the structure and properties of the interfacial protein films formed with different bulk protein concentrations. We demonstrate that a diffusion-controlled adsorption occurs at low bulk protein concentration for helianthinin whereas this mechanism occurs whatever the bulk concentration for gliadins. Surface pressure-induced film relaxation through conformation changes of proteins at the air-water interface is identified for gliadin whereas surface aggregation is observed at high helianthinin concentration. Overall, our experimental results highlight that structural flexibility of proteins appears as a key factor for their interfacial activity.

The origin of the unique rheological properties of wheat gluten, the water-insoluble protein fraction of wheat grain, is crucial in bread-making processes and questions scientists since the 18th century. Gluten is a mixture of two types of proteins, monomeric gliadins and polymeric glutenins, formed by subunits linked via disulfide bonds. To better understand the respective role of gliadins (Gli) and glutenins (Glu) in the supramolecular structure of gluten and its link to rheology, we have developed a model gluten system using a food-grade solvent, which allows quantitative comparisons with theoretical models for synthetic polymers [1]. Thanks to an experimental protocol based on a liquid-liquid phase separation, we can extract, from industrial gluten, gluten protein fractions with contrasted mass ratios Glu/Gli (from 0.04 to 2). Stable gluten protein suspensions in a water/ethanol mixture solvent over a wide range of concentrations can be produced. Using scattering techniques, we demonstrate that blends of Gli and Glu exhibit features characteristic of branched flexible polymer chains in a good solvent, and form in a dilute regime large Glu-rich protein assemblies [2]. In the semi-dilute regime, we evidence the existence of large zones (of typical size 60 nm) rich in hydrogen bonds [3]. We show that hydrogen bonds are responsible for the spontaneous sample gelation, whose concentration dependence can be quantitatively accounted using percolation theories developed for polymer gels [4]. Overall, our experimental results illustrate the relevance of model gluten gels to unravel the unique and complex behavior of gluten. [1] Banc, Dahesh, Wolf, Morel, Ramos. Journal of Cereal Science 75, 175 (2017). [2] Dahesh, Banc, Duri, Morel, Ramos. J Phys Chem B 118, 11065 (2014). [3] Banc, Charbonneau, Dahesh, Appavou, Fu, Morel, Ramos. Soft Matter 12, 5340 (2016). [4] Dahesh, Banc, Duri, Morel, Ramos. Food Hydrocolloids, 52, 1 (2016).

not available

Gliadins are edible wheat storage proteins well known for their surface active properties1, 2. Although their foaming3 and emulsifying4 capability is useful in food industry, the physical mechanisms of their adsorption at an interface are not well understood and the resulting structure of the protein interfacial films not yet well characterized. In this talk, we will present experimental results on the interfacial properties of acidic gliadin solutions studied over 4 decades of concentrations from 0.01 up to 110 mg/ml.Dynamic pendant drop tensiometry reveals that the surface pressure of gliadin solutions builds up in a multistep process. We show that the series of curves of the time evolution of alpha.time collected at different protein concentrations can be merged onto a single master curve when surface pressure is plotted as a function of alpha.time where t is the time elapsed since the formation of the air/water interface and alpha is a shift parameter that varies with the bulk protein concentration as a power law with an exponent 1.6. The existence of a master curve indicates that the surface pressure is the relevant parameter to characterize the interfaces covered with gliadin proteins.Optical and elastic properties of the interfaces are studied by dilatational rheology and ellipsometry and provide a consistent physical picture of the adsorption processes. Correlated evolutions of ellipsometry and rheological properties show a simple and progressive coverage of the interface by individual proteins at low surface pressure. This stage is followed, at higher surface pressure, by conformational rearrangements of the protein film, which are identified by a strong increase of the dissipative viscoelastic properties of the film concomitantly with an anomalous evolution of its optical profile that we have quantitatively rationalized. In the last stage, at even higher surface pressure, the optical profile is not modified while the elasticity of the film dramatically increases resulting from the gelation of the film due to the formation of intermolecular bonds. [1] J.Ornebro, T. Nylander, A-C Eliasson (2000). Journal of Cereal Science 31, 195-221[2] R. C. A Keller, R. Orsel, R. J. Hamer (1997). Journal of Cereal Science 25, 175-183[3] Martin A. Bos, Bertus Dunnewind, Ton van Vliet (2003). Colloids and Surfaces B 31, 95-105[4] Y.Popineau, F.Pineau, P. Evon, S. Bérot (1999). Nahrung 6, S. 361-367