49 research outputs found
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
Adsorption of MultiLamellar tubes with a temperature tunable diameter at the air-water interface: a process driven by the bulk properties
The behavior at the air/water interface of multilamellar tubes made of the
ethanolamine salt of the 12-hydroxy stearic acid as a function of the
temperature has been investigated using Neutron Reflectivity. Those tubes are
known to exhibit a temperature tunable diameter in the bulk. We have observed
multilamellar tubes adsorbed at the air/water interface by specular neutron
reflectivity. Interestingly, at the interface, the adsorbed tubes exhibit the
same behavior than in the bulk upon heating. There is however a peculiar
behavior at around 50\degree for which the increase of the diameter of the
tubes at the interface yields an unfolding of those tubes into a multilamellar
layer. Upon further heating, the tubes re-fold and their diameter re-decrease
after what they melt as observed in the bulk. All structural transitions at the
interface are nevertheless shown to be quasi-completely reversible. This
provides to the system a high interest for its interfacial properties because
the structure at the air/water interface can be tuned easily by the
temperature
Polysaccharide/Surfactant complexes at the air-water interface – Effect of the charge density on interfacial and foaming behaviors
International audienceThe binding of a cationic surfactant (hexadecyltrimethylammonium bromide, CTAB) to a negatively charged natural polysaccharide (pectin) at air-solution interfaces, was investigated on single interfaces and in foams, versus the linear charge densities of the polysaccharide. Beside classical methods to investigate polymer/surfactant systems, we applied, for the first time concerning these systems, the analogy between the small angle neutron scattering by foams and the neutron reflectivity of films to measure in situ film thicknesses of foams. CTAB/pectin foam films are much thicker than that of the pure surfactant foam film but similar for highly and lowly charged pectin/CTAB systems despite the difference in structure of complexes at interfaces. The improvement of the foam properties of CTAB bound to pectin is shown to be directly related to the formation of pectin-CTAB complexes at the air-water interface. However, in opposition to surface activity, there is no specific behavior for the highly charged pectin: foam properties depend mainly upon the bulk charge concentration, while the interfacial behavior is mainly governed by the charge density of pectin. For the highly charged pectin, specific cooperative effects between neighboring charged sites along the chain are thought to be involved in the higher surface activity of pectin/CTAB complexes. A more general behavior can be obtained at lower charge density either by using a lowly charged pectin or by neutralizing the highly charged pectin in decreasing pH.
La vision artificielle appliquée aux produits céréaliers
2. ed. chap. 2 Mention d'Ă©dition : 2. ed.National audienc
Rôle des agrégats de protéines dans la formation et la stabilisation de mousses
La formation de mousses aqueuses à partir de solutions de protéines dépend de la nature des protéines et de leur capacité à stabiliser les interfaces eau/air. Durant les procédés industriels, les protéines se présentent sous forme agrégée dans des structures complexes du fait des traitements thermomécaniques qui leur sont appliqués. Mais, seule une partie des protéines est agrégée et cela peut influencer considérablement les propriétés moussantes. L objectif de ce travail de thèse était de mettre en évidence dans quelle mesure ces agrégats en absence de protéines non agrégées sont capables de stabiliser les mousses et cela en relation avec les différents niveaux d organisation de la mousse (interfaces eau/air et film interfacial). Des agrégats de différentes tailles ont été obtenus par dénaturation thermique de la b-lactoglobuline, protéine majeure du lactosérum dont les mécanismes d agrégation sont connus. Quelle que soit leur taille, les agrégats en absence de protéines non agrégées conduisent à des mousses moins stables que celles de protéines non agrégées, due à la faible capacité des agrégats às adsorber aux interfaces. En présence de protéines non agrégées, les agrégats sont capables d améliorer les propriétés moussantes. La viscoélasticité des couches interfaciales adsorbées est renforcée et un réseau de type gel est formé dans les films interfaciaux, rigidifiant l interface et ralentissant le drainage de la mousse. Dans le cas où le réseau de type gel ne peut être formé, les agrégats peuvent se localiser dans les bords de Plateau de la mousse, ralentissant ainsi l écoulement du liquideThe foam formation depends on the nature of the protein and on their capacity to stabilize the air/water interfaces. During food processes, proteins undergo thermomechanical treatments leading to their aggregation in self-assembled structures. However, only a given fraction of the proteins is aggregated and this part may be considerably influence the foaming properties. This thesis aims at considering the aggregation part in the foam formation and stabilization at the different foam scales (air/water interface and foam film). Protein aggregates with different sizes were obtained by heat-induced denaturation of b-lactoglobulin, major whey protein for which the aggregation is well-known. Whatever the aggregate size, solutions containing exclusively protein aggregates lead to less stable foams than that of non aggregated proteins alone, due to the low capacity of aggregates to adsorb at the air/water interfaces. With non aggregated proteins, aggregates are able to improve the foaming properties. The viscoelasticity of the interfacial adsorbed layers is reinforced and a gel-like network is formed within the foam film, rigidifying the interface and slowing down the foam drainage. In the case of the gel-like network cannot be formed, protein aggregates can locate in the Plateau borders, slowing down the flow in the foamNANTES-BU Sciences (441092104) / SudocSudocFranceF
Aggregation of proteins : its role in foam structuration and stabilization
National audienc
Effect of protein aggregates on foaming properties of beta-lactoglobulin
International audienceOur paper aims at determining the respective part of protein aggregates and non-aggregated proteins in the foam formation and stability of P-lactoglobulin. We report results on fractal aggregates formed at neutral pH and strong ionic strength (aggregates size from 30 to 190 nm). Pure aggregates and mixtures of non-aggregated/aggregated proteins at varying ratios were used. The capacity of aggregates to form and stabilize foams has been studied in relation with their ability to absorb at air/water interfaces. Our results show that protein aggregates are not able by themselves to improve the foaming properties but participate to a better foam stabilization in the presence of non-aggregated proteins. Non-aggregated proteins appear to be necessary to produce stable foams. We have shown that the amount and the size of aggregates had an influence on the drainage rate
Synthesising gold nanoparticles within bola fatty acid nanosomes
International audienceWe report on the synthesis of gold nanoparticles (AuNP) stabilized by a layer of mercapto and/or hydroxyl bola palmitic acid-tetrabutyl ammonium salts (TBAOH) which form nanosomes in water. Mixing both bola fatty acids in water in various proportions allowed to tune the nanoparticle diameter from 1 to 10 nm using NaBH4 as a reductor. Those nanoparticles could be phase transferred to dichloromethane by adding a more hydrophobic counter-ion than TBAOH, its derivative with octyl chains (TOAOH). Finally, we used those AuNP to formulate emulsions, the stability of which was followed as a function of particle size and time. The emulsions were stable but creamed after several hours. We conclude that bola fatty acid nanosomes are then good candidates to synthesize gold nanoparticles dispersed either in water, organic solvents and emulsions
Assessment of the quality of wheat milling products by fluorescence video imaging
National audienc
Particle size characterisation of in-flow milling products by video image analysis using global features
19 ref.International audienc