Structural and Shear Characteristics of Adsorbed (beta)-Casein and Monoglyceride Mixed Monolayers at the Air/Water Interface

In this work, we have analyzed the structural (structure, topography, reflectivity, miscibility, and interactions) and surface shear characteristics of an adsorbed (beta)-casein and monoglyceride (monopalmitin and monoolein) mixed films at the air/water interface. Different and complementary interfacial techniques (surface film balance, Brewster angle microscopy, and interfacial shear rheology) have been utilized. The structural, topographical, and shear characteristics of the mixed films are dependent on the surface pressure and the composition of the mixed film. The surface shear viscosity ((eta)s) varies greatly with the surface pressure. Generally, the greater the surface pressure, the greater the values of (eta)s. At higher surface pressures, collapsed (beta)-casein residues may be displaced from the interface by monoglyceride molecules with important repercussions on the shear characteristics of the mixed films. Shear-induced change in the topography of monoglyceride and (beta)-casein domains, on one hand, and segregation between domains of the film forming components, on the other hand, were also observed. The displacement of the (beta)-casein by the monoglycerides is facilitated under shear conditions, especially for (beta)-casein-monoolein mixed films.