Stability and viscoelastic properties of mixed lupin-whey protein at oil-water interfaces depend on mixing sequence

There has been increasing interest in understanding how to utilize plant proteins for foods. In this study, the adsorption dynamics and emulsifying properties of lupin proteins were studied, in isolation and in combination with whey proteins, to evaluate potential synergies occurring at the interface. Analysis of the viscoelastic properties of lupin-whey protein interfaces demonstrated that lupin protein highly surface active compared to whey proteins, particularly the most soluble lupin proteins. Furthermore, in the mixed systems, the elastic and viscous properties of the interfaces differed depending on the order of protein addition. The interfacial structures were also probed by studying displacement by surfactant. Emulsions prepared with both lupin and whey proteins showed reduced bridging flocculation when compared to lupin-only stabilized emulsions. Emulsions stabilized with whey proteins only, on the other hand, did not show any bridging flocculation. The creaming stability of bulk emulsions was also dependent on the order of protein addition. Transmission electron microscopy images confirmed the presence of aggregates when lupin protein isolate was employed as the main emulsifier. This work highlights the potential benefits of using protein blends, to control the emulsion properties by altering the order and point of protein addition during processing.