Matthieu Pouzot

Structure of Heat-Induced β-Lactoglobulin Aggregates and their Complexes with Sodium-Dodecyl Sulfate

We report on the conformation of heat-induced bovine beta-lactoglobulin (betalg) aggregates prepared at different pH conditions, and their complexes with model anionic surfactants such as sodium dodecyl sulfate (SDS). The investigation was carried out by combining a wide range of techniques such as ultra small angle light scattering, static and dynamic light scattering, small angle neutron scattering, small-angle X-ray scattering, electrophoretic mobility, isothermal titration calorimetry (ITC) and transmission electron microscopy. Three types of aggregates were generated upon heating betalg aqueous dispersions at increasing pH from 2.0 to 5.8 to 7.0: rod-like aggregates, spherical aggregates, and worm-like primary aggregates, respectively. These aggregates were shown not only to differ for their sizes and morphologies, but also for their internal structures and fractal dimensions. The main differences between aggregates are discussed in terms of the ionic charge and conformational changes arising for betalg at different pHs. The formation of complexes between SDS and the various protein aggregates at pH 3.0 was shown to occur by two main mechanisms: at low concentration of SDS, the complex formation occurs essentially by ionic binding between the positive residues of the protein and the negative sulfate heads of the surfactant. At complete neutralization of charges, precipitation of the complexes is observed. Upon further increase in SDS concentration, complex formation of SDS and the protein aggregates occurs primarily by hydrophobic interactions, leading to (i) the formation of an SDS double layer around the protein aggregates, (ii) the inversion of the total ionic charge of each individual protein aggregate, and (iii) the complete redispersion of the protein aggregate-SDS complexes in water. Remarkably, the SDS double layer around the protein aggregates provides an efficient protective shield, preventing precipitation of the aggregates at any possible pH values, including those values corresponding to the isoelectric pH of the aggregates.

Oleoylethanolamide-Based Lyotropic Liquid Crystals as Vehicles for Delivery of Amino Acids in Aqueous Environment

We have investigated the phase behavior of self-assembled lyotropic liquid crystals (LC) formed by ternary mixtures of oleoylethanolamide (OEA), water and arginine. OEA, a natural analog of the endogenous cannabinoid anandamide involved in the peripheral regulation of feeding, was selected as a main component due to its capacity to induce efficient decreases in food intake and gains in body mass. Arginine was selected as representative hydrophilic amino acid and added to the OEA-water mixture at different concentrations. The phase diagrams were determined by combining cross-polarized optical microscopy and small angle x-ray scattering. First, the phase diagram for the OEA-water system was determined. It was shown that these two compounds give rise to reverse Ia3d double gyroid and reverse Pn3m double diamond cubic phases existing in bulk over a large window of temperature and composition, and that for water content beyond 25% Pn3m coexisted with excess water. Successively, the influence of arginine as guest molecule in the water channels of the reverse LC was investigated. For the sake of comparison, results for the OEA-water-arginine system were compared with analog series of OEA-water-glucose. The results showed that, at a fixed water content and temperature, the phase behavior of the liquid crystalline phases is strongly dependent on arginine concentration. In more detail, arginine could be encapsulated in the bulk OEA-water LC up to 2.0% wt, whereas transitions from Ia3d to Pn3m cubic phase were observed with increasing arginine concentration. Interestingly, upon an increase of water concentration beyond 20-25%, Pn3m phase started to coexist with excess water releasing the arginine in external water solution. Quantitative measurements of arginine content inside the LC water channels and in the excess external water solution revealed a complete release of the amino acid, demonstrating that the investigated lyotropic liquid crystalline systems can be used as ideal vehicles for the delivery of functional hydrophilic active molecules in aqueous environment.

Tuneable thickness barriers for composite o/w and w/o capsules, films, and their decoration with particles

Oil-in-water and water-in-oil capsules, and flat membranes of tuneable thickness and composition were prepared in one single facile step, based on the interfacial complexation between chitosan and anionic phosphatidic fatty acids. The phosphatidic acid molecules were introduced via the oil phase. The thickness of the capsule shell or the membrane grows by a diffusion-controlled mechanism, hence can be tuned using e.g. concentration and formation time parameters. A mechanism is proposed to explain the observed behavior. The capsule size is set by the emulsification conditions applied. Microfluidic methods proved useful for the generation of hollow capsules of uniform size and thickness in one step. The capsules and membranes display remarkable integrity over several years in a pH window 2–14. The thickness can easily reach several micrometres within an hour for the wet capsule shell or membrane, which explains the high interfacial rheological properties measured. Hence various processes can be envisaged after their formation. The simple preparation opens the way to tailored, environment-responsive composite systems for fabricating biopolymer-based materials for various applications. The capsules could be washed from the surrounding continuous phase and placed into one of arbitrary choice. Furthermore, the surface of the w/o capsules and of the membranes could be decorated by particles that attach to the water/oil interface with a high energy. The choice of the particle functionality is left open.