Interfacial properties of whey protein hydrolysates monitored by quartz crystal microbalance with dissipation

Whey protein hydrolysate (WPH) can be used to develop hypoallergenic foods. However, the stabilization mechanism of WPH-stabilized emulsion is not fully understood. Here, a real-time quartz crystal microbalance with dissipation monitoring (QCM-D) was used in conjunction with a rheometer to investigate the interfacial properties of WPH. Initially, the properties of WPH with different (6 %, 8 %, 10 %, 12 % and 14 %) degree of hydrolysis (DH) were investigated. 8 %-WPH demonstrated superior emulsifying (11.49 m²/g, 81.34 min) and foaming properties (14.00 %, 7.78 %). Subsequently, the stability of different WPH-stabilized emulsions were examined. 8 %-WPH emulsion exhibited the lowest centrifugal precipitation rate (4.50 %) and Turbiscan stability index (2.24). Additionally, the 8 %-WPH promoted the adsorption and retention of molecules at the interface, which effectively reduced the interfacial tension. QCM-D measurement further proved that the 8 %-WPH possessed excellent adsorption mass and viscoelasticity. Finally, we characterized the interface-adsorbed WPH. The 8 %-WPH exhibited the highest surface hydrophobicity (1072.60) and flexibility (0.22). Notably, the 8 %-WPH showed the highest β-sheet (41.11 %). This led to stronger interactions between neighboring interfacial WPH molecules, which protected the emulsion droplets from destabilizing factors. Nevertheless, excessive hydrolysis (10 %-14 %) caused WPH molecules aggregation, which consequently diminished the viscoelasticity of the interfacial film and the emulsion stability.