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International audience; Proteins are widely used to stabilize emulsions, and plant proteins have raised increasing interest for this purpose. The interfacial and emulsifying properties of proteins depend largely on their molecular properties. We used fluorescence spectroscopy to characterize the conformation of food proteins from different biological origins (dairy or pea) and transformation processes (commercial or lab-made isolates) in solution and at the oil-water interface. The fourth derivative of fluorescence spectra provided insights in the local environment of tryptophan (Trp) residues and thus in the protein structure. In emulsions, whey proteins adsorbed with their Trp-rich region at the oil-water interface. Proteins in the commercial pea isolate were present as soluble aggregates, and no changes in the local environment of the Trp residues were detected upon emulsification, suggesting that these structures adsorb without conformational changes. The lab-purified pea proteins were less aggregated and a Trp-free region of the vicilin adsorbed at the oil-water interface.

9 pages; International audience; Unsaturated fatty acids may be extracted from various agricultural resources and are widely used as soaps in the industry. However, there also exist a large variety of saturated and hydroxy fatty acids in nature, but their metal salts crystallize at room temperature in water, hampering their use in biological and chemical studies or for industrial applications. Addition of guanidine hydrochloride (GuHCl) to sodium salt of myristic acid has been shown to prevent its crystallization in water, forming stable flat bilayers at room temperature. Herein, we extend this finding to two other saturated fatty acids (palmitic and stearic acids) and two hydroxyl fatty acids (juniperic and 12 hydroxy stearic acids) and study more deeply (by using small angle neutron scattering) the supramolecular assemblies formed in both saturated and hydroxyl fatty acid systems. In addition, we take the advantage that crystallization no longer occurs at room temperature in the presence of GuHCl to study the foaming and emulsifying properties of those fatty acid dispersions. Briefly, our results show that all fatty acids, even juniperic acid, which is a bola lipid, are arranged in a bilayer structure that may be interdigitated. Depending on the nature of the fatty acid, the systems exhibit good foamability and foam stability (except for juniperic acid), and emulsion stability was good. Those findings should be of interest for using saturated long chain (and hydroxyl) fatty acids as surfactants for detergency or even materials chemistry.

6 pages; International audience; Ultrastable foams with an optimal foamability have been obtained using hydroxyl fatty acids tubes. The stabilization results from the adsorption of monomers at the air-water interface preventing coalescence and coarsening and from the presence of tubes in the Plateau borders limiting the drainage. Upon heating, tubes transit to micelles, which induces foam destabilization. Such foams are thus the first to have a temperature tunable stability.

10 pages; International audience; There is a growing interest for constructing supramolecular hollow tubes from amphiphilic molecules. Aqueous solutions of the ethanolamine salt of 12-hydroxystearic acid are known to form tubes of several tens of micrometers in length with a temperature-tunable diameter. However, the phase behavior of this system has not been fully studied. Herein, we report the variation of various physico-chemical parameters on the self-assembling properties of this system. The effects of the ionic strength, ethanol, doping with other lipids, pH, concentration, and the fatty acid/ethanolamine molar ratio R were investigated by both phase-contrast microscopy and DSC. We observed the formation of tubes in a wide range of parameters. For instance, the molar ratio R can be modified from 2/3 to 5/2 without altering the formation of tubes. In some but not all cases, the tube diameter still varied with temperature. These findings show that tubes form under various experimental conditions. This should increase the interest in producing such self-assemblies from low-cost fatty acids.

6 pages; International audience; We report on dispersions of fatty acid-lysine salts in aqueous solutions which are further used to produce foams. The alkyl chain length is varied from dodecyl to stearic. In aqueous solutions, the lysine salt of the dodecyl chain yields an isotropic solution, probably micelles, whereas for longer alkyl chains, vesicles formed but crystallized upon resting at room temperature or when kept at 4 C. Solid stateNMRshowed that in vesicles fatty acids are embedded in a lamellar arrangement passing from a gel to a fluid state upon heating; the transition temperature at which it occurs was determined by DSC. Those results are confirmed by small-angle neutron scattering which also give additional information on the bilayer structure. Incredibly stable foams are obtained using the palmitic acid/Lys salt whereas for other alkyl chain length, poor or no foam is formed. We conclude that the foamability is related to the phase behavior in aqueous solution.

International audience; A mixture between 1% sodium myristate and guanidine hydrochloride at a molar ratio of 1 in water forms a gel of membranes below a phase transition of ca. 21°C and a viscous limpid and isotropic solution above. As observed by both TEM and AFM, we report the formation of interconnected superstructures in that latter phase. Those assemblies exhibit a size of ca. 4-40nm width and several tens of [mu]m length with unexpected disconnections and reconnections between them having the appearance of an anastomosis-like superstructure.

International audience; In surfactant systems, the major role of the nature of the counter-ion on the surfactant behavior is well-known. However, the effect of the molar ratio between the surfactant and its counter-ion is less explored in the literature. We investigated the effect of the molar ratio (R) between 12-hydroxystearic acid (12-HSA) and various alkanolamines as a function of the temperature in aqueous solution from the molecular scale to the mesoscale. By coupling microscopy techniques and small angle neutron scattering, we showed that 12-HSA self-assembled into multilamellar tubes and transitioned into micelles at a precise temperature. This temperature transition depended on both the molar ratio and the alkyl chain length of the counter-ion and could be precisely tuned from 20°C to 75°C. This thermal behaviour was investigated by differential scanning calorimetry and wide angle X-ray scattering. We highlighted that the transition at the supramolecular scale between tubes to micelles came from two different mechanisms at the molecular scale as a function of the molar ratio. At low R, with an excess of counter-ion, the transition came from the chain melting phenomenon. At high R, with an excess of 12-HSA, the transition came from both the chain melting process and the surface melting process of the hydrogen bonds. At the mesoscale, this transition of supramolecular assemblies from tubes to micelles, delimited a regime of high bulk viscosity, with a regime of low viscosity.