Surface tension of protein and insoluble lipids at the air‐aqueous phase interface

Abstract

The surface activity of bovine serum albumin (BSA) in water and aqueous solutions of ethanol (0.5, 1.0, and 2.0 M) and sucrose (0.5 and 1.0 M) has been investigated over a range of protein concentrations (5-1.10 −5 , % w/w). The surface tension data were determined by the Wilhelmy plate method. Surface data at low protein concentrations indicate a low surface activity, which rises to a plateau as the monolayer is saturated at higher protein concentrations. The protein concentration and surface tension at the plateau depend on the aqueous phase composition. The effect of aqueous phase composition on BSA-lipid interactions has been investigated by spreading an insoluble lipid (monostearin or monoolein) on a film of BSA previously adsorbed on the interface. The existence of protein-lipid interactions depends on the protein/lipid ratio. The surface activity of mixed BSA-lipid films is determined by the lipid because the surface pressure of the mixed film is the same as the lipid equilibrium spreading pressure, and the monolayer is not saturated by BSA. However, the surface activity of mixed BSA-lipid films is determined by BSA as the monolayer is saturated by the protein.

Correlating Surface Activity with Interface-Induced Aggregation in a High-Concentration mAb Solution

“…Nonetheless, the maximum surface pressure values attained over the course of 60 min showed that once the interface was saturated by protein molecules, these values did not depend on bulk concentration. This is in accordance with previous studies showing that, beyond the interface saturation point, the equilibrium surface pressure of protein solutions is irrespective of bulk concentration. , …”

“…This is in accordance with previous studies showing that, beyond the interface saturation point, the equilibrium surface pressure of protein solutions is irrespective of bulk concentration. 35,36 During experiments with samples at the highest concentration, we noticed the formation of a gel-like film around the probe, suggesting the formation of an interfacial viscoelastic network. Although no visible film was observed when dealing with lower concentrations, it does not mean the absence of a protein network.…”

Dewetting of Polymer Films Controlled by Protein Adsorption

“…The surface activity of BSA is related to its affinity for the amphiphilic air/aqueous phase interface, driven by hydrophobic BSA surface regions, whereas polar BSA domains stay in contact with the aqueous phase. 38 , 39 Surface tension decreases from the pure PBS dilution value only when a significant protein amount is adsorbed at the air interface with at least half monolayer surface coverage. 38 …”

Structural Characteristics of Monopalmitin Monolayers Spread on Aqueous Sugar Solutions

“…The expansion of monoglyceride monolayers on aqueous sugar solutions is higher for monopalmitin than for monostearin. This fact has important consequences for other interfacial characteristics, such as stability, rheology, and mobility, (30 -33), and has a role on the interactions between emulsifiers (proteins and lipids) at the interface (33)(34)(35)(36), which are important factors in food dispersions (emulsions and foams) formation, properties, and stability. …”