Structure, Miscibility, and Rheological Characteristics of β-Casein−Monoglyceride Mixed Films at the Air−Water Interface

Abstract

In this work we have used different and complementary interfacial techniques (surface film balance, Brewster angle microscopy, and interfacial dilatational rheology) to analyze the static (structure, morphology, reflectivity, miscibility, and interactions) and dynamic characteristics (surface dilatational properties) of beta-casein and monoglyceride (monopalmitin and monoolein) mixed films spread on the air-water interface. The static and dynamic characteristics of the mixed films depend on the interfacial composition and the surface pressure. At higher surface pressures, collapsed beta-casein residues may be displaced from the interface by monoglyceride molecules with important repercussions on the interfacial characteristics of the mixed films. From the frequency dependence of the surface dilatational properties, we have elucidated the relationships between interfacial dilatational rheology and changes in molecular structure, interactions, miscibility, and relaxation phenomena in protein-monoglyceride mixed films.

Flow-Induced Molecular Segregation in β-Casein−Monoglyceride Mixed Films Spread at the Air−Water Interface

“…Structural and Topographical Characteristics. Results derived from π− A isotherms (Figure A) in the modified Wilhelmy type trough are in good agreement with those obtained in the same unmodified trough with pure β-casein and monopalmitin monolayers and in the Langmuir type trough with the same β-casein, monopalmitin, and β-casein−monopalmitin mixed films. , Briefly, the results of π− A isotherms confirm that β-casein monolayers at the air−water interface adopt two different structures and the collapse phase. At low surface pressures, β-casein molecules may exist as trains with all amino acid segments located at the interface .…”

“…In this region, a mixed monolayer of monoglyceride and β-casein may exist. However, at surface pressures higher than that for β-casein collapse, the π− A isotherm for the mixed monolayer at X MP = 0.5 was parallel to that of monopalmitin, which demonstrates that the arrangement of the monopalmitin hydrocarbon chain in mixed monolayers is practically the same. , That is, at higher surface pressures, collapsed β-casein residues may be displaced from the interface by monopalmitin molecules. Moreover, the mixed film collapses at a surface pressure similar to that for monopalmitin, which is an indication of the immiscibility between film-forming components at the highest surface pressures.…”

“…The main difference was observed in the region after the β-casein collapse (20 mN/m < π < 45 mN/m), because the relative reflectivity of the mixed film was lower than for pure β-casein. This suggests that monopalmitin is able to displace β-casein residues from the interface toward a sublayer beneath the monopalmitin monolayer. , The peaks in the relative reflectivity are due to the fact that in this region domains of pure β-casein (with high I ) and monopalmitin (with low I ) passed alternatively through the spot where this measurement was performed. Near to the collapse of the mixed films (at 45 mN/m < π < 52 mN/m), the peaks in relative reflectivity practically disappeared and the I values decreased to those typical for a pure monopalmitin monolayer.…”

Characterization of Monoolein Langmuir Monolayers Spread at The Salt Solution/Air Interface

“…Due to the compactness of the molecules on barrier compression and also the phenomenon of liftoff surface pressure observed for monoolein lipid monolayer has been shown in Figure 4(a). On the experimental side, the values of salt-free monoolein experimental studies for the area per lipid for monoolein monolayers were recorded for various temperature ranges [33][34][35]. To validate, our observed value for the area per lipid is therefore in good agreement with the available experimental data at room temperature [34].…”

“…The slit complement to the interactions between van der Waals and the hydrocarbon chain of the lipid and hydrogen bond links at the interface form the network with the lipid polar head group. This enhances the attraction or repulsion of the uniform distributive single-molecule lipid layer, particularly the affinity to change the subphase of salt in the bulk aqueous process [35,49]. It may also be associated in the bulk aqueous phase with monolayer molecular loosening by collapse and dissolution, as seen for the same lipid propagation to the aqueous solution [50].…”