Interfacial protein layer

Some of the areas where interfacial protein layers dominate the boundary chemistry are reviewed, and we introduce some nondestructive armlytical methods which can be used simultaneously and/or sequentially to detect and characterize the microscopic amounts of matter at protein or other substrates which spontaneously acquire protein conditioning films. Examples include collagen and gelatin, synthetic polypeptides, nylons, and the biomedically important surfaces of vessel grafts, skin, tissue, and blood. The importance of prerequisite adsorbed films of proteins during thrombus formation, cell adhesion, use of intrauterine contraceptives, development of dental adhesives, and prevention of maritime fouling is discussed. Specifics of protein adsorption at solid/liquid and gas/liquid interfaces are compared. 

Lee, S.-H., Lefevre, T., Subirade, M., and Paquin, P. (2009). Effects of ultra-high pressure homogenization on the properties and structure of interfacial protein layer in whey protein-stabilized emulsion. Food Chem. 113,191-195. 

Bos, M.A., van Vliet, T. (2001). Interfacial rheological properties of adsorbed protein layers and surfactants. Advances in Colloid and Interface Science, 91, 437-471. 

A situation that commonly occurs with food foams and emulsions is that there is a mixture of protein and low-molecular-weight surfactant available for adsorption at the interface. The composition and structure of the developing adsorbed layer are therefore strongly influenced by dynamic aspects of the competitive adsorption between protein and surfactant. This competitive adsorption in turn is influenced by the nature of the interfacial protein-protein and protein-surfactant interactions. At the most basic level, what drives this competition is that the surfactant-surface interaction is stronger than the interaction of the surface with the protein (or protein-surfactant complex) (Dickinson, 1998 Goff, 1997 Rodriguez Patino et al., 2007 Miller et al., 2008 Kotsmar et al., 2009). 

Figure 8.11 Elastic modulus versus interfacial water activity aws of protein layers at the air-water interface ( ) adsorbed p-casein ( ) adsorbed a-lact-albumin ( ) adsorbed p-lactoglobulin ( ) spread p-lactoglobulin. Reproduced from Damodaran (2004) with permission.

Protein-polysaccharide complexation affects the surface viscoelastic properties of the protein interfacial layer. Surface shear rheology is especially sensitive to the strength of the interfacial protein-polysaccharide interactions. Experimental data on BSA+ dextran sulfate (Dickinson and Galazka, 1992), asi-casein + high-methoxy pectin (Dickinson et al., 1998), p-lactoglobulin + low-methoxy pectin (Ganzevles et al., 2006), and p-lactoglobulin + acacia gum (Schmitt et al., 2005) have all demon-... 

Although the present finding that BLM formed from simple lipids alone can possess intrinsic low yb without the presence of protein layers, it in no sense invalidates the bimolecular leaflet model. Our study does suggest, however, that natural lipids such as lecithin when in a bilayer configuration could exist in natural membranes to give the results of low yt observed by earlier workers, which has been thought essential in the development of the concept of the bimolecular lipo-protein model based upon interfacial tension measurements. 

It is commonly stated that the first readily observable event at the interface between a material and a biological Quid is protein or macromolecule adsorption. Clearly other interactions precede protein adsorption water adsorption and possibly absorption (hydration effects), ion bonding and electrical double layer formation, and the adsorption and absorption of low molecular weight solutes — such as amino acids. The protein adsorption event must result in major perturbation of the interfacial boundary layer which initially consists of water, ions, and other solutes. 

When pure protein films are stretched, the change in interfacial area is dissipated across the film, due to the cohesive nature of the adsorbed protein layer and the deformability of the adsorbed protein molecules. 

The interfacially bound protein layer on fat globules is influenced greatly by the emulsifier and hydrocolloid content as well as by processing conditions. 

During ageing of the mix, interfacial milk protein hydration also increases simultaneously with protein desorption from the fat globules. The water content of the isolated cream layers after centrifugation of ice cream mix can be analyzed by Karl Fischer titration. From such analyses, interfacial protein hydration can be calculated (Figure 13). 

Both hydrocolloids and emulsifiers increase the water-binding capacity in the mix (increased % of hydrogen atoms with low T2 and decreased T2 values). A synergistic effect is observed when both ingredients are present. From studies described earlier in this chapter, the effect of hydrocolloids is assumed to be due to simple water binding and increased thickness of protein layers around the fat globules, whereas the effect of emulsifiers may be due to the increased hydration of interfacially bound protein as well as increased hydration of polar groups of emulsifier at the oil-water interface. 

Abstract. Surface pressure/area isotherms of monolayers of micro- and nanoparticles at fluid/liquid interfaces can be used to obtain information about particle properties (dimensions, interfacial contact angles), the structure of interfacial particle layers, interparticle interactions as well as relaxation processes within layers. Such information is important for understanding the stabilisation/destabilisation effects of particles for emulsions and foams. For a correct description of II-A isotherms of nanoparticle monolayers, the significant differences in particle size and solvent molecule size should be taken into account. The corresponding equations are derived by using the thermodynamic model of a two-dimensional solution. The equations not only provide satisfactory agreement with experimental data for the surface pressure of monolayers in a wide range of particle sizes from 75 pm to 7.5 nm, but also predict the areas per particle and per solvent molecule close to the experimental values. Similar equations can also be applied to protein molecule monolayers at liquid interfaces. 

A great problem is that for (vlsco-) elastic interfacial layers, such as spread or adsorbed protein layers, any major deformation partly destroys the network at the interface. This is expected to cause a strong inhomogeneity of the local shear rate and interfacial viscosity over the gap between the measuring body and the outer vessel. Then the obtained apparent 7) reflects some average over the local values. For a small deformation, as usually applied in creep or relaxation experiments, the problem of inhomogeneous deformation of the interface is reduced. Moreover, it is smaller for a smaller gap width between the measuring body emd the outer vessel. 

Interactions between proteins and polysaccharides give rise to various textures in food. Protein-stabilized emulsions can be made more stable by the addition of a polysaccharide. A complex of whey protein isolate and carboxymethylcellulose was found to possess superior emulsifying properties compared to those of the protein alone (Girard et al., 2002). The structure of emulsion interfaces formed by complexes of proteins and carbohydrates can be manipulated by the conditions of the preparation. The sequence of the addition of the biopolymers can alter the interfacial composition of emulsions. The ability to alter interfacial structure of emulsions is a lever which can be used to tailor the delivery of food components and nutrients (Dickinson, 2008). Polysaccharides can be used to control protein adsorption at an air-water interface (Ganzevles et al., 2006). The interface of simultaneously adsorbed films (from mixtures of proteins and polysaccharides) and sequentially adsorbed films (where the protein layer is adsorbed prior to addition of the polysaccharide) are different. The presence of the polysaccharide at the start of the adsorption process hinders the formation of a dense primary interfacial layer (Ganzelves et al., 2008). These observations demonstrate how the order of addition of components can influence interfacial structure. This has implications for foaming and emulsifying applications. 

Uniaxial compression of a model protein layer (a) transient bonds (bmax = 0-3) nd (b) permanent bonds (fcmax — °°)- The snapshots of the system on the left correspond to 50% compression. Dark spheres represent particles not directly adsorbed at the interface. The area fraction P as function of the interfacial area A and the corresponding interfacial stress in the direction of compression are shown on the right. The thick lines correspond to a system of particles that do not form bonds at aU. The arrows indicate the direction of compression. 

Such behavior can be explained as follows when batch adsorption is performed above the volume phase transition temperature (1) the mechanical entrapment of protein molecules in the interfacial shell layer due to the poly(NlPAM) tentacles (octopus-like adsorption process) and... 

Ismailova, V.N., "Stmcture Formation and Rheological Properties of Proteins and Surface-Active Polymers of Interfacial Adsorption Layers" in Progress in Surface and Membrane Science 13(1979)... 

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