Dynamic adsorption and interfacial rheology of whey protein isolate at oil-water interfaces: Effects of protein concentration, pH and heat treatment

The effects of bulk protein concentration, C-p, (0.01, 0.1, 1 wt%), pH (3, 4.7 and 7) and heat treatment (unheated or 95 degrees C for 30 min) on whey protein isolate (WPI) stabilized interfaces were examined. The interfacial pressure and shear rheology of WPI-stabilized sunflower oil-water (o/w) interfaces were characterized using a pendant drop tensiometer and a rheometer equipped with a Du Nouy ring. The rate of WPI adsorption was faster at higer C-p and pH 3. Heat-enhanced surface activity was more pronounced at pH 7 compared to pH 3 as a result of greater heat stability of WPI at acidic pH. The elastic modulus of WPI stabilized interfaces increased with Cp (<= 0.1 wt%). A further increase in C-p (to 1 wt%) resulted in monolayer collapse and weaker films. Non-heated (NHT) WPI formed less elastic interfacial films at pH 3 than at pH7. Heat treatment enhanced the elastic behavior of interfacial films with longer relaxation times. This may be associated with the formation of intermolecular beta-sheets. The knowledge gained on the nature of WPI-stabilized interfaces can be used to better understand the stability of dairy emulsions during subsequent processing, digestion or storage.

Automated summary

The study revealed that the stability of whey protein isolate-stabilized interfaces is affected by protein concentration, pH, and heat treatment. Higher concentrations and acidic pH resulted in faster WPI adsorption rates, while heat treatments may enhance the elastic behavior of the interfaces. Furthermore, an increase in protein concentration could lead to monolayer collapse and weaker films.