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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

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DOI: 10.1016/j.jcs.2017.04.005
WoS: 000404792200025
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Model gluten gels

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The structure of polymer nanocomposites has important consequences on final properties, like e.g.mechanical reinforcement. The structure of the hard filler phase is usually characterized by electronmicroscopy and small-angle X-ray scattering (SAXS), and we will review recent examples of fillerstructure in model and industrial nanocomposites. The chain conformation can only bemeasured by small-angle neutron scattering (SANS) with isotopic substitution. Over the past 15 years,considerable efforts have been dedicated to such measurements. Results appear to converge towardGaussian statistics of chains, unperturbed by the presence of filler NPs, and exceptions seem to be dueto system-dependent effects. In nearly all studies, however, unexplained pollution of the scatteringdata in the low-q range has been observed, in spite of careful contrast-matching.In this study, the conformation of polymer chains in silica-latex nanocomposites has been studiedunder zero-average contrast (ZAC) conditions using SANS. Samples have been prepared by dryingcolloidal suspensions of silica and polymer nanoparticles (NPs) for two different silica NPs (radius of5 and 15 nm) and two chain masses (17 and 100 kg/mol). By mixing appropriate amounts ofhydrogenated and deuterated polymer, chain scattering contrast is introduced, and in principle silicascattering is suppressed. However, the SANS scattering intensities displayed distinct deviations at lowangles. Comparison of the SANS and SAXS intensities proves that the measurement of chain structureby SANS is perturbed by unwanted silica contributions, i.e., the silica is ‘mysteriously’ visible. Aquantitative model rationalizing these contributions for the first time is proposed. It is based on astatistical H/D-mismatch in the local environment of the silica NPs. Such a mismatch leads to theexistence of a nanometer-thick polymer shell surrounding silica NPs, which carries H/D contrast andthereby produce an undesired scattering contribution. These shells are presumably maintained by thereduced mobility of polymer close to interfaces or attractive polymer-silica interactions. The effect ofunwanted filler scattering is NP size-dependent − it is pronounced only for smaller beads. This isprobably why ZAC turned out to be so difficult with polymer nanocomposites.

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We propose a quantitative approach to probe the spatial heterogeneities of interactions in macromolecular gels, based on a combination of small angle X-ray (SAXS) and neutrons (SANS) scattering. We investigate the structure of model gluten protein gels and show that the gels display radically different SAXS and SANS profiles when the solvent is (at least partially) deuterated. The detailed analysis of the SANS signal as a function of the solvent deuteration demonstrates heterogeneities of sample deuteration at different length scales. The progressive exchange between the protons (H) of the proteins and the deuteriums (D) of the solvent is inhomogeneous and 60 nm large zones that are enriched in H are evidenced. In addition, at low protein concentration, in the sol state, solvent deuteration induces a liquid/liquid phase separation. Complementary biochemical and structure analyses show that the denser protein phase is more protonated and specifically enriched in glutenin, the polymeric fraction of gluten proteins. These findings suggest that the presence of H-rich zones in gluten gels would arise from thepreferential interaction of glutenin polymers through a tight network of non-exchangeable intermolecular hydrogen bonds.

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Ref Arxiv: 1605.05867
DOI: 10.1039/c6sm00710d
WoS: 000378934400011
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The structure of model gluten protein gels prepared in ethanol/water is investigated by small angle X-ray (SAXS) and neutrons (SANS) scattering. We show that gluten gels display radically different SAXS and SANS profiles when the solvent is (at least partially) deuterated. The detailed analysis of the SANS signal as a function of the solvent deuteration demonstrates heterogeneities of sample deuteration at different length scales. The progressive exchange between the protons (H) of the proteins and the deuteriums (D) of the solvent is inhomogeneous and 60 nm large zones that are enriched in H are evidenced. In addition, at low protein concentration, in the sol state, solvent deuteration induces a liquid/liquid phase separation. Complementary biochemical and structure analyses show that the denser protein phase is more protonated and specifically enriched in glutenin, the polymeric fraction of gluten proteins. These findings suggest that the presence of H-rich zones in gluten gels would arise from the preferential interaction of glutenin polymers through a tight network of non-exchangeable intermolecular hydrogen bonds.