The rheological properties of bovine β-Lactoglobulin stabilized oil/water interfaces depend on the protein's quaternary structure

Structural manipulation of beta-lactoglobulin through processes such as heat treatment and complexation with other molecules has proven fruitful in industrial formulations. To fully appreciate the ramifications of such methods on protein interfacial adsorption we have investigated assemblies of beta-lactoglobulin at oil/water interfaces predominantly at pH 3 and at different conditions of ionic strength, salt type and temperature. These parameters were tuned to vary the relative amounts of two native species, namely, monomer and its smallest aggregate, the dimer, while the interface was monitored using rheology and tensiometry. Unfolding of beta-lactoglobulin at the interface triggers the formation of disulfide linkages between the free thiol groups of two monomers which are located at cys121. In this way, monomers pair up to form discrete assemblies of two beta-lactoglobulin molecules (non-native dimers) that are not interconnected further and this is reflected in the absence of a viscoelastic layer in solutions with high monomer concentrations. Native dimers however form primary particles capable of forming two thiol bonds allowing the formation of extended networks. A higher concentration of dimers increases the final interfacial elastic strength of the network. This fundamental relation between the quaternary structure of beta-lg and its subsequent interfacial network suggests a possible interfacial role in its biological function.

Automated summary

Structural manipulation of beta-lactoglobulin through processes like heat treatment and complexation has shown success in industrial formulations. The formation of disulfide linkages between monomers at the interface triggers assembly into non-native dimers, while native dimers form extended networks, impacting the interfacial elastic strength. The relationship between the quaternary structure of beta-lg and its interfacial network suggests a potential role in its biological function.