Interfacial Properties of Mixed β-Lactoglobulin−SDS Layers at the Water/Air and Water/Oil Interface

Abstract

The adsorption behavior of the beta-lactoglobuline has been studied in the presence of the anionic surfactant sodium dodecylsulfate (SDS) and compared for two different interfaces, water/air and water/hexane. The fitting of experimental data (adsorption isotherms) by a mixed adsorption model and the determination of structural parameters such as the molecular area occupied by the protein-surfactant complex and the surfactant molecules at the interface allowed to have a better understanding of the composition and as a consequence the behavior of the mixed interfacial layer. The parameters obtained for the mixtures are similar to those obtained separately for the single components, but the comparison of the both interfaces has shown significant differences. Much higher concentration of complex is found at the water/hexane interface, which is the result of a better affinity of the protein for this interface. A higher penetration of the protein into the oil phase and the presence of interactions between protein-surfactant complexes and free surfactant molecules stabilize the interface preventing its replacement by the SDS molecules. Rheological experiments show a decrease of the visco-elastic modulus at both interfaces with increasing SDS concentration. But at the water/oil interface, contrary to the water/air interface at which the replacement of the protein has been clearly observed, this decrease is attributed to changes of complex properties. At high SDS concentrations, an increase of the hydrophilic character due to hydrophobic interactions with the surfactant molecules leads to an increase in the mobility of the complex, which favors its desorption upon increased competition by the surfactant.

Tensiometry and dilational rheology of mixed β-lactoglobulin/ionic surfactant adsorption layers at water/air and water/hexane interfaces

“…Since even saturated SDS or DoTAB layers do exhibit much lower |E|-values than those for the BLG layer at the studied concentration (10 À6 M), the fact that the trends of P and |E| in the mixtures keep opposite directions, i.e. decrease of |E| with increasing P, is consistent with the continuous increase of the interfacial amount of SDS due to competitive adsorption and subsequent replacement of the protein (protein/surfactant complexes) from both the W/A [26][27][28] and the W/H interfaces [27,36] by unbound surfactant molecules.…”

Effect of surfactant SDS on DMSO transport across water/hexane interface by molecular dynamics simulation

“…The interfacial tension versus the SDS concentration at C DMSO ¼ 4:3% is plotted in Fig. 2, and for comparison we also plot the distributions of interfacial tensions in the absence of DMSO from both the current simulation and available experimental results (Pradines et al, 2009). First, at zero DMSO concentration, the overall simulation curve agrees well with experimental results at various SDS concentrations.…”

“…It has been shown that competitive adsorption at the interface plays different roles in the water/air and water/oil interfaces (Pradines et al, 2009). Specifically, when amphiphilic surfactants such as SDS are adsorbed at the water/air interface, despite an increase in the interfacial width, the hydrophobic tails of SDS are repelled from both sides, forming a disordered structure at the interface (Dominguez and Berkowitz, 2000).…”

“…The experimental result is fromPradines et al (2009), and the concentration of DMSO is set zero or C DMSO ¼ 4:3%. Curves are drawn to guide the eye.…”

Microfluidic methods to study emulsion formation

“…%). This may be caused by a higher affinity of protein for oil than for air resulting in a higher interfacial protein concentration with a more compact and protective structure at the oil-water interface (Pradines et al 2009;Maldonado-Valderrama et al 2005). This foam experiment shows that it is possible to form protein-stabilised air bubbles in a microfluidic device and subsequently measure their coalescence stability.…”