Interfacial property of protein

Rouimi, S., Schorsch, C., Valentini, C., Vaslin, S. (2005). Foam stability and interfacial properties of milk protein-surfactant systems. Food Hydrocolloids, 19, 467 178. 

Emulsification is a stabilizing effect of proteins a lowering of the interfacial tension between immiscible components that allow the formation of a protective layer around oil droplets. The inherent properties of proteins or their molecular conformation, denaturation, aggregation, pH solubility, and susceptibility to divalent cations affect their performance in model and commercial emulsion systems. Emulsion capacity profiles of proteins closely resemble protein solubility curves and thus the factors that influence solubility properties (protein composition and structure, methods and conditions of extraction, processing, and storage) or treatments used to modify protein character also influence emulsifying properties. 

Interfacial phenomena with special reference to biological systems. Chapter discussions include properties of proteins, polar lipids and polysaccharide at interfaces. A variety of spectrophotometric methods to resolve interfacial membrane structures are described in detail. 

Surface properties of proteins in general, 296-298 (table) purification methods based on, 272 Surface tension and interfacial properties, 609-628. see also Interfaces Surfactants, see also Interfacial tension definition and adsorption kinetics of, 617-618, 639... 

Wilkie summarized the important interfacial properties of gelatin (7), and Stenzel and co-workers prepared a similar review of the features of collagen which underlie that protein s fundamental importance as a biomaterial (8, 9). 

The complexity and diversity of structures in the native proteins eluded any attempt to produce some simple conformation that accounted for their interfacial properties. The study of synthetic polypeptides with non-polar side chains has provided good evidence to support the view that the a-helix can be stable at the air-water interface (5), and it is therefore possible that the interfacial denaturation of proteins is mainly a loss of the tertiary structure (6, 7, 8). Since for a typical protein an a-helix takes up about the same area per residue as the p conformation, it can be accommodated as easily. Moreover, like the p conformation but unlike a more randomly coiled structure, it is linear and therefore compatible with a plane surface without loss of configurational entropy (5). In this respect a plane surface may favor an ordered over a more random structure. The loss of solubility of the spread protein can then be attributed to intermolecular association between hydrophobic side chains exposed as a result of the action of the interface on the polar exterior of the molecules. 

Direct, unmediated electrochemistry of redox enzymes has interested many researchers in several aspects. Understanding of the thermodynamics, kinetics, stoichiometry, and interfacial properties of redox enzymes is obviously important. The most attractive aspect, however, is the use of enzyme electrodes as novel electrochemical biosensors and their applications to bioreactors and biofuel cells. Although the observation of direct electrochemistry of small redox proteins has become almost commonplace as the consequence of extensive research over the past decade, the corresponding study with larger redox enzymes has proved more elusive. The difficulty lies mainly in that the redox centers are located sufficiently far from the outermost... 

Interfacial films of protein coagulate under certain conditions, the properties of the coagulated protein being quite different from those of the original crystalline protein. F or example, solubility is lost. 

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)... 

Thorough study of states and properties of protein layers at various interfaces and development of new methods for analyzing the interfacial state. 

The properties of proteins that promote emulsion formation are also important in the creation of foams. Poole and Fry [44] suggested that the ideal protein for foaming would posses high surface hydro-phobicity, high solubility, and a low net charge at the pH of the food product. To exhibit functional performance, the protein must reach the air/water interface. Rapid diffusion and unfolding at the interface is required to lower the interfacial tension between the air and the water phase [45]. Factors that increase the rate of protein diffusion have also been reported to enhance protein foaming [46,16]. 

The surface active properties of proteins are related to their ability to lower the interfacial tension between air/water or oil/water interfaces. Surface activity is a function of the ease with which proteins can diffuse to, adsorb at, unfold, and rearrange at an interface (11,12). Thus, size, native structure and solubility in the aqueous phase are closely correlated with the surface activity of proteins in model systems (13-16). 

Monolayer techniques were used to characterize the interfacial properties of the resultant Fractions. Fraction I contained highly cohesive complexes that did not unfold at the interface and had an average diameter of 9.1 nm. These particles are thought to represent submicelles, previously identified in micelle formation. Fraction II showed interfacial properties that are characteristic of spread casein monomers, and contained mainly a -casein. The results are discussed in relation to casein interactions and micellar formation. Mixed monolayers of sodium caseinate/glyceride monostearate (NaCas/GMS) were also examined at different composition ratios. The results show that for low surface pressures (0-20 mNm ), there is a condensation ascribable to hydrophobic interactions in the mixed film. At high surface pressures, the hydrophobic interaction is modified and the protein is expelled from the monolayer into the subphase. These results are discussed in relation to emulsion stability. 

PAQUIN ET AL. Interfacial Properties of Milk Casein Proteins... 

The work presented in this paper shows the usefulness of the mono-layer technique to determine the interfacial properties of caseins. Characterization of casein Fractions at the air-water interface contributed to a better understanding of the nature of casein interactions in micellar organization. Preparation of NaCas/GMS mixed films provided relevant information about the manner in which proteins might be involved in the structure of fat globule membrane. 

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