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

    Year: 2021

    Journal: Food Hydrocolloids, Volume 120, NOV

    Authors: Ramamirtham, Sashikumar; Whitby, Catherine P.; Zare, Davoud; Weeks, Mike; Williams, Martin A. K.

    Organizations: New Zealand Ministry of Business, Innovation & Employment (MBIE) [C10X1502]; AgResearch Ltd, NZ

    Keywords: Whey proteins; Interfacial rheology; Acidified milk drinks; Disulfide bond; Protein adsorption

    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.
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