Early film formation in protein-stabilised emulsions: Insights from a microfluidic approach

In conventional emulsification devices, interface formation and stabilisation occur within milliseconds. Protein network formation at liquid-liquid interfaces starts at time scales similar to those of droplet formation in conventional emulsification devices (i.e., in milliseconds). Classical methods, like drop tensiometry, do not allow measurements at these time scales. Using a tailor-made microchip, we probed droplet deformation to study the interfacial rheological properties of droplets, within time scales ranging from 0.16 to 1 s. We further investigated the coalescence stability of droplets at the same time scales. Whey protein isolate (WPI), pea protein isolate (PPI), or their blends were used as emulsifiers at 0.01–1 g/L. The rheological properties of the protein-interfaces showed that early network formation takes place (<1 s). WPI-stabilised interfaces were mechanically stronger compared to PPI-stabilised interfaces, and WPI-stabilised droplets were much less prone to coalescence than their PPI counterparts. Although the blend-stabilised films showed high interconnectivity, this did not prevent droplet coalescence, probably due to structural heterogeneity. The insights obtained with the tailor-made microfluidic devices help to capture effects at short time scales and are relevant to unravel phenomena occurring in large scale processing.