Foams Prepared from Whey Protein Isolate and Egg White Protein: 1. Physical, Microstructural, and Interfacial Properties

Abstract

Foams were prepared from whey protein isolate (WPI), egg white protein (EWP), and combinations of the 2 (WPI/EWP), with physical properties of foams (overrun, drainage 1/2 life, and yield stress), air/water interfaces (interfacial tension and interfacial dilatational elasticity), and foam microstructure (bubble size and dynamic change of bubble count per area) investigated. Foams made from EWP had higher yield stress and stability (drainage 1/2 life) than those made from WPI. Foams made from mixtures of EWP and WPI had intermediate values. Foam stability could be explained based on solution viscosity, interfacial characteristics, and initial bubble size. Likewise, foam yield stress was associated with interfacial dilatational elastic moduli, mean bubble diameter, and air phase fraction. Foams made from WPI or WPI/EWP combinations formed master curves for stability and yield stress when normalized according to the above-mentioned properties. However, EWP foams were excluded from the common trends observed for WPI and WPI/EWP combination foams. Changes in interfacial tension showed that even the lowest level of WPI substitution (25% WPI) was enough to cause the temporal pattern of interfacial tension to mimic the pattern of WPI instead of EWP, suggesting that whey proteins dominated the interface. The higher foam yield stress and drainage stability of EWP foams appears to be due to forming smaller, more stable bubbles, that are packed together into structures that are more resistant to deformation than those of WPI foams.