Relationship between structure and rheological properties of mixed BSA/Tween 80 adsorption layers at the air/water interface

Rheological properties of interfacial layers play a very important role for the stability of various colloidal food systems such as foams or emulsions. The ability of liquid lamellas between neighbouring elements of the dispersed phase to resist deformations upon collision can determine the coalescence rate and, therefore, the life time of the whole colloidal system. The same properties, in turn, are closely related to the structure of the interfacial layers on both sides of the liquid lamella. The composition of interfacial layers and the way in which they were formed are crucial factors influencing their structural and consequently their rheological properties. Hence, one of the most important tasks of modern food science is the development of compositions of interfacial active compounds being able to modify the structure of these layers in a controlled way. From this point of view protein/surfactant mixtures are very promising systems. In the present contribution the rheological, structural and mechanical properties of mixed adsorption layers comprised of bovine serum albumin (BSA) and Tween 80 at the air/water interface were studied by surface shear rheometry, ellipsometry and tensiometry (drop profile analysis), respectively. The dependencies of shear visco-elasticity, thickness and refractive index of the respective adsorbed layers as well as the surface tension on the total concentration and subphase composition were considered. On this basis, conclusions about possible changes in the layer structure and their relation to the rheological properties were drawn. Applicability of “orogenic” displacement model developed earlier for penetration of a spread protein layer by soluble surfactants was discussed for the current case of competitive adsorption.