Behavior of plant-dairy protein blends at air-water and oil-water interfaces

Recent work suggests that using blends of dairy and plant proteins could be a promising way to mitigate sustainability and functionality concerns. Many proteins form viscoelastic layers at fluid interfaces and provide physical stabilization to emulsion droplets; yet, the interfacial behavior of animal-plant protein blends is greatly underexplored. In the present work, we considered pea protein isolate (PPI) as a model legume protein, which was blended with well-studied dairy proteins (whey protein isolate (WPI) or sodium caseinate (SC)). We performed dilatational rheology at the air-water and oil-water interface using an automated drop tensiometer to chart the behavior and structure of the interfacial films, and to highlight differences between films made with either blends, or their constituting components only. The rheological response of the blend-stabilized interfaces deviated from what could be expected from averaging those of the individual proteins and depended on the proteins used; e.g. at the air-water interface, the response of the caseinate-pea protein blend was similar to that of PPI only. At the oil-water interface, the PPI and WPI-PPI interfaces gave comparable responses upon deformation and formed less elastic layers compared to the WPI-stabilized interface. Blending SC with PPI gave stronger interfacial layers compared to SC alone, but the layers were less stiff compared to the layers formed with WPI, PPI and WPI-PPI. In general, higher elastic moduli and more rigid interfacial layers were formed at the air-water interface, compared to the oil-water interface, except for PPI.