Foaming properties of protein/pectin electrostatic complexes and foam structure at the nanoscale

The foaming properties, foaming capacity and foam stability, of soluble complexes of pectin and a globular protein, napin, have been investigated with a "Foamscan" apparatus. Complementary, we also used SANS with a recent method consisting in an analogy between the SANS by foams and the neutron reflectivity of films to measure in situ film thickness of foams. The effect of ionic strength, of protein concentration and of charge density of the pectin has been analysed. Whereas the foam stability is improved for samples containing soluble complexes, no effect has been noticed on the foam film thickness, which is almost around 315 {\AA} whatever the samples. These results let us specify the role of each specie in the mixture: free proteins contribute to the foaming capacity, provided the initial free protein content in the bulk is sufficient to allow the foam formation, and soluble complexes slow down the drainage by their presence in the Plateau borders, which finally results in the stabilisation of foams

Spatial structure and composition of polysaccharide-protein complexes from Small Angle Neutron Scattering

We use Small Angle Neutron Scattering (SANS), with an original analysis method, to obtain both the characteristic sizes and the inner composition of lysozyme-pectin complexes depending on the charge density. Lysozyme is a globular protein and pectin a natural anionic semiflexible polysaccharide with a degree of methylation (DM) 0, 43 and 74. For our experimental conditions (buffer ionic strength I = 2.5 10-2 mol/L and pH between 3 and 7), the electrostatic charge of lysozyme is always positive (from 8 to 17 depending on pH). The pectin charge per elementary chain segment is negative and can be varied from almost zero to one through the change of DM and pH. The weight molar ratio of lysozyme on pectin monomers is kept constant. The ratio of negative charge content per volume to positive charge content per volume, -/+, is varied between 10 and 0.007. On a local scale, for all charged pectins, a correlation peak appears at 0.2 {\AA}-1 due to proteins clustering inside the complexes. On a large scale, the complexes appear as formed of spherical globules with a well defined radius of 10 to 50 nm, containing a few thousands proteins. The volume fraction Phi of organic matter within the globules derived from SANS absolute cross-sections is around 0.1. The protein stacking, which occurs inside the globules, is enhanced when pectin is more charged, due to pH or DM. The linear charge density of the pectin determines the size of the globules for pectin chains of comparable molecular weights whether it is controlled by the pH or the DM. The radius of the globules varies between 10 nm and 50 nm. In conclusion the structure is driven by electrostatic interactions and not by hydrophobic interactions. The molecular weight also has a large influence on the structure of the complexes since long chains tend to form larger globules. This maybe one reason why DM and pH are not completely equivalent in our system since DM 0 has a short mass, but this may not be the only one. For very low pectin charge (-/+ = 0.07), globules do not appear and the scattering signals a gel-like structure. We did not observe any beads-on-a-string structure

Gelation studies of a cellulose-based biohydrogel: the influence of pH, temperature and sterilization.

International audienceThe present paper investigates the rheological properties of silated hydroxypropylmethylcellulose (Si-HPMC) biohydrogel used for biomaterials and tissue engineering applications. The general property of this modified cellulose ether is the occurrence of self-hardening due to silanol condensation subsequent to a decrease in pH (from 12.4 to nearly 7.4). The behavior of unsterilized and sterilized Si-HPMC solutions in diluted and concentrated domains is first described and compared. In addition, the influence of physiological parameters such as pH and temperature on the rate of the gelation process is studied. In dilute solution, the intrinsic viscosity ([eta]) of different pre-steam sterilization Si-HPMC solutions indicates that macromolecular chains occupy a larger hydrodynamic volume than the post-steam sterilization Si-HPMC solutions. Although the unsterilized Si-HPMC solutions demonstrate no detectable influence of pH upon the rheological behavior, a decrease in the limiting viscosities (eta(0)) of solutions with increasing pH is observed following steam sterilization. This effect can be explained by the formation of intra- and intermolecular associations during the sterilization stage originating from the temperature-induced phase separation. The formation of Si-HPMC hydrogels from injectable aqueous solution is studied after neutralization by different acid buffers leading to various final pHs. Gelation time (t(gel)) decreases when pH increases (t(gel) varies from 872 to 11s at pH 7.4 and 11.8, respectively). The same effect is observed by increasing the temperature from 20 to 45 degrees C. This is a consequence of the synergistic effect of the increased reaction rate and acid buffer diffusion. pH and temperature are important parameters in the gelation process and their influence is a key factor in controlling gelation time. By adapting the gel parameters one could propose hydrogels with cross-linking properties adapted to clinical applications by controlling the amount of pH of neutralization and temperature

Micelle formation, gelation and phase separation of amphiphilic multiblock copolymers

The phase behaviour of amphiphilic multiblock copolymers with a large number of blocks in semidilute solutions is studied by lattice Monte Carlo simulations. The influence on the resulting structures of the concentration, the solvent quality and the ratio of hydrophobic to hydrophilic monomers in the chains has been assessed explicitely. Several distinct regimes are put in evidence. For poorly substituted (mainly hydrophilic) copolymers formation of micelles is observed, either isolated or connected by the hydrophilic moieties, depending on concentration and chain length. For more highly substituted chains larger tubular hydrophobic structures appear which, at higher concentration, join to form extended hydrophobic cores. For both substitution ratios gelation is observed, but with a very different gel network structure. For the poorly substituted chains the gel consists of micelles cross-linked by hydrophilic blocks whereas for the highly substituted copolymers the extended hydrophobic cores form the gelling network. The interplay between gelation and phase separation clearly appears in the phase diagram. In particular, for poorly substituted copolymers and in a narrow concentration range, we observe a sol-gel transition followed by an inverse gel-sol transition when increasing the interaction energy. The simulation results are discussed in the context of the experimentally observed phase properties of methylcellulose, a hydrophobically substituted polysaccharide.Comment: 14 pages, 14 figures; Soft Matter (2011

De nouveaux modèles pour l'alimentation de demain

National audienceDans le cadre du projet européen DREAM, de nouveaux modèles ont été développés permettant de simuler l'impact de procédés de transformation agro-alimentaire sur les propriétés nutritionnelles ou microbiologiques des aliments. Les entreprises de l'agro-alimentaire, notamment les PME, disposeront ainsi de modèles informatiques à la fois génériques et suffisamment réalistes pour optimiser leurs processus de fabrication ou pour l'élaboration de recettes innovantes. Un colloque de clôture du projet organisé du 24 au 26 juin 2013 à Nantes a rendu compte des résultats obtenus

2.7. La qualité des produits : les apports de la modélisation

Les enjeux de la qualité des produits Comprendre l’origine de la qualité* des produits alimentaires nécessite de comprendre à la fois l’impact de nombreux paramètres externes, aussi bien « au champ » que lors des procédés de fabrication, et des paramètres intrinsèques à l’aliment comme sa composition et son organisation structurale qui résulte des interactions entre les molécules le composant. L’enjeu pour maîtriser la qualité consiste à relier les critères qui caractérisent l..

Face à une nouvelle donne, repenser l'innovation avec tous les acteurs devient incontournable

National audienceAlors que les industries agro-alimentaires (IAA) représentent le premier secteur industriel en France et en Europe elles sont aussi celui dont la part du chiffre d’affaire consacrée aux dépenses R&D est le plus faible. Cette particularité, si elle peut s’expliquer par la faible taille de la majorité des entreprises, par la faiblesse des marges, par le poids de contraintes réglementaires fortes, par les attentes contradictoires des consommateurs…, n’en reste pas moins un élément de fragilité majeur pour l’avenir alors que l’on attend pour 2011 et 2012 une croissance molle et une hausse du prix des matières premières agricoles et de tous les intrants

Etude par diffusion des rayons X aux petits angles du mecanisme de coagulation-floculation d'une silice colloiedale en presence d'une solution de chlorure d'aluminium partiellement neutralisee

SIGLET 56553 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Ion complexation of biopolymers : macromolecular structure and viscoelastic properties of gels

9 ref.International audienc

Polysaccharide-metal interactions

chap. 9International audienc