Interfacial tension, between protein

Interfacial Tension Between Protein and Water A Missing Chapter in Drug Design 219... 

To summarize, three conclusions transpire from the nanoscale thermodynamics results (a) The interfacial tension between protein and water is patchy and the result of both nanoscale confinement of interfacial water and local redshifts in dielectric relaxation (b) the poor hydration of polar groups (a curvature-dependent phenomenon) generates interfacial tension, a property previously attributed only to hydrophobic patches and (c) because of its higher occurrence at protein-water interfaces, the poorly hydrated dehydrons become collectively bigger contributors to the interfacial tension than the rarer nonpolar patches on the protein surface. 

Figure 4c shows that the amount of adsorbed proteins is rapidly saturated within several minutes of exposing serum-containing medium to a surface. Albumin, the most abundant serum protein, was expected to preferentially adsorb onto the surfaces during early time points. Then, adsorbed albumin was expected to be displaced by cell adhesion proteins. To investigate the effect of preadsorbed albumin displacement on cell adhesion, SAMs were first exposed to albumin then, HUVECs suspended in a serum-supplemented medium were added [21, 42]. Very few cells adhered to hydrophobic SAMs that had been pretreated with albumin, due to the large interfacial tension between water and the hydrophobic surfactant-like surface. Albumin was infrequently displaced by the cell adhesive proteins Fn and Vn. One the other hand, HUVECs adhered well to hydrophilic SAM surfaces that had been preadsorbed with albumin. In that case, the preadsorbed albumin was readily displaced by cell adhesive proteins. 

Go and n being the interfacial tension between oil and water, and the surface pressure due to the adsorption of proteins and emulsifier, respectively. Combining equations 1-4, we obtain. 

Kinsella (13, 14) summarized present thinking on foam formation of protein solutions. When an aqueous suspension of protein ingredient (for example, flour, concentrate, or isolate) is agitated by whipping or aeration processes, it will encapsulate air into droplets or bubbles that are surrounded by a liquid film. The film consists of denatured protein that lowers the interfacial tension between air and water, facilitating deformation of the liquid and expansion against its surface tension. 

When proteins unfold and expose their hydrophobic regions, the interfacial tension between air and the aqueous phase is lowered facilitating deformation of the liquid into an impervious film that enhances aeration or foamability of the solution. This is affected by pH, ionic strength, and temperature, and protein, oil, and carbohydrate concentrations. Water and fat absorption involve similar physicochemical and environmental properties, and reportedly have been affected by the size of ingredient particles. 

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. 

Keshavarz, E. and Nakai, S. 1979. The relationship between hydrophobicity and interfacial tension of proteins. Biochim. Biophys. Acta 576, 269-279. 

Jackson, R. H. and Pallansch, M. J. 1961. Influence of milk proteins on interfacial tension between butteroil and various aqueous phases. J. Agr. Food Chem. 9, 424-427. 

Emulsion Capacity and Stability. The emulsion capacities of the three protein preparations are shown in Table IV. and again both the unheated and microwave treated samples were significantly superior to that of the hot water process. Although it is difficult to relate these data to those of other workers, since a wide variety of conditions are employed for measuring this property, it has generally been found that emulsifying properties are related to the aqueous solubility of proteins (7.) which further bears on the capacity of proteins to lower interfacial tension between hydrophobic and hydrophilic components. 

Introduction of additional negative charge into proteins by reaction with dicarboxylic anhydrides resulted in an increased solubility in neutral and weak alkaline aqueous solutions [11-13], A positive correlation between solubility and the ability of a protein to emulsify has been documented by some authors [59-62], An increase in protein solubility would encourage a rapid migration to and adsorption of the protein at the water-oil interface. The adsorption would, in turn, lower the interfacial tension between the water and the oil and stabilize the emulsion [63 J. In fact, improved emulsifying properties have been found after succinylation or citraconylation of a large number of food proteins such as myofibrillar fish proteins [10, fish protein... 

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). 

Fig. 2.8 Interfacial tension of p-lactoglobulin (P-LG), whey protein isolate (WPI) and whey protein hydrolysates (WPH) with varying degree of hydrolysis (DH) at the air-water interface during 15 min (left) and right) interfacial tension after injection of the protein solution into a droplet of water (protein content /e/t 1.2 wt% right, approximately 0.4 wt% final protein content after injection). The interfacial pressure is defined as the difference between the interfacial tension of water and the interfacial tension with protein present...

Interfacial tensions between water and various oils (Table 9) were found to be significantly lower in comparison to other hydrocolloids or well-known emulsifying proteins. 

It is well known that hydrogels are characterized by a very good biocompatibility °, mostly because of the low interfacial tension between the hydrogel surface and biological fluids that minimizes protein adsorption and cell adhesion . 

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