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

Abstract

In this work, we have analyzed the structural (structure, topography, reflectivity, miscibility, and interactions) and surface shear characteristics of an adsorbed β-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 (η s ) varies greatly with the surface pressure. Generally, the greater the surface pressure, the greater the values of η s . At higher surface pressures, collapsed β-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 β-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 β-casein by the monoglycerides is facilitated under shear conditions, especially for β-casein-monoolein mixed films.

Monoglycerides and β-Lactoglobulin Adsorbed Films at the Air−Water Interface. Structure, Microscopic Imaging, and Shear Characteristics

“…The structural characteristics of adsorbed β-lactoglobulin−monoolein mixed monolayers were essentially different to those of monopalmitin in the mixture, as deduced from π− A isotherms (Figure ). Briefly, as expected, , β-lactoglobulin−monoolein mixed films at surface pressures lower than that for β-lactoglobulin collapse (at π < 25.9 mN/m) adopt a liquid-like-expanded structure, as for pure components. There was a monolayer expansion due to the presence of monoolein in the mixture.…”

Protein Displacement by Monoglyceride at the Air−Water Interface Evaluated by Surface Shear Rheology Combined with Brewster Angle Microscopy

“…Topographical and Shear Characteristics of Protein and Monoglyceride Adsorbed Mixed Films. The time evolution of η s during the flow of β-casein− and β-lactoglobulin−monoglyceride adsorbed mixed monolayers through the canal as a function of surface pressure is shown in Figures and , respectively. , Similar results were observed for mixtures of monoglycerides and sodium caseinate . It can be seen that (i) at π < π e β-CS and at π < π e β-LG (at 10 and 20 mN/m), the values of η s are between those of pure monolayer components but a little lower.…”

“…While shear viscosity may contribute appreciably to the long-term stability of dispersions, dilatational rheology plays an important role in short-term stability. − ,− Moreover, the ability of the protein to resist displacement by emulsifiers is closely linked to the surface dilatational rheology, whereas the precise form of the displacement is considered to be more closely related to the surface shear behavior. , Interfacial shear rheology is most useful for polymer and mixed polymer surfactant adsorption layers and insoluble monolayers and gives access to interaction forces in two-dimensional layers. , In addition, the shear may induce heterogeneity and segregation between protein and lipid domains at the interface during the flow of the monolayer. The flow-induced orientational alignment has recently been the topic of abundant research in a variety of spread monolayers, − but less is known about adsorbed films. − …”

Penetration of β-Lactoglobulin into Monoglyceride Monolayers. Dynamics, Interactions, and Topography of Mixed Films

“…Moreover, the penetration of β-lactoglobulin into a monopalmitin monolayer can be also visualized at a microscopic level by the reduction of mobility of LC monopalmitin domains, which correlates with the higher shear viscosity of β-lactoglobulin and monopalmitin mixed films at the higher surface pressures , as the penetration process progresses.…”