Effect of Xanthoceras sorbifolium bunge leaves saponins on the foaming properties of whey protein isolate at varying pHs: Correlation between interface, rheology, and foaming characteristics

The interaction between whey protein isolate (WPI) and saponins plays a key role in regulating and improving foam properties. In this study, the influences of Xanthoceras sorbifolium Bunge leaves saponins (XLS) on the foaming properties of WPI were characterized. Results revealed that 0.2 or 0.3% XLS could significantly increase the particle size and turbidity, as well as significantly decrease the protein solubility. The spectrum results showed that there was an interaction between WPI and XLS, which caused the change in protein structure and exposed more hydrophobic groups. Importantly, WPI with 0.3% XLS significantly increased the surface hydrophobicity and decreased the surface tension, resulting in better foaming ability and foam stability. Moreover, the rheological determination suggested that WPI with XLS increased both the apparent viscosity and viscoelasticity. The best foaming performance of WPI was achieved with 0.3% XLS at pH 3, along with the formation of the most compact, smallest, and densest bubbles. According to the classification of mixed conditions suggested by principal component analysis and hierarchical clustering analysis, WPI had good scores in the presence of both 0.2% and 0.3% XLS at pH 3, suggesting that XLS is a promising acidic foam additive applied to WPI food foam.