Lactoglobulin, surface viscosities

The structure of adsorption layers is of great importance during preparation of food foams and emulsions. These problems have been studied in [144] for protein adsorption at the liquid/gas interfaces and in [145] for liquid/liquid interfaces. Due attention is also paid to the interaction of typical emulsifiers and proteins during preparation of food emulsions [146 - 147]. Addition of an oil-soluble emulsifier to proteins during preparation of w/o emulsions [146] increased the emulsification rate, but at high concentrations decreased it due to the increase in oil viscosity. In this case, the emulsifier displaced (3-casein from the surface easier than P-lactoglobulin. However, there was no complete displacement into the aqueous phase since multiple emulsions were formed, as mentioned above [142 -143]. Hence, the ehoice of the surfactant/protein ratio is important. 

FIG. 2 Competitive adsorption of P-lactoglobulin + Tween 20 at the oil-water interface. R is the Tween 20/P-lactoglobulin molar ratio. F (triangles), concentration of P-lactoglobulin on the surface of oil droplets in the emulsion (0.45 wt% protein, 10 wt% n-tetradecane, pH 7) T (circles), apparent surface shear viscosity after 5 h adsorption from a 10 wt% aqueous protein solution (pH 7, 25°C). (From Ref. 23.)... 

At relatively low concentrations, gum arabic yields solutions that are essentially Newtonian in behavior and have very low viscosities compared to other polysaccharides of similar molecular mass. This behavior is similar to that of globular proteins. The intrinsic viscosities at pH 5.5 of gum arabic solutions are similar to those of P-lactoglobulin. Randall et al. [158] and Williams et al. [148] concluded that the AGP fraction is responsible for the gum s emulsifying ability. Consequently, relatively high concentrations of gum arabic are required to produce stable emulsions of relatively small droplet size. At a lower gum arabic concentration, there is insufficient surface-active material to fully coat all the droplets. Therefore, it has been concluded that although gum arabic is basically a polysaccharide, its interfacial and emulsifying properties are derived from its proteinaceous nature. 

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