pH-dependent aggregation behavior and emulsion stability in sodium caseinate-faba bean protein hybrid systems

This study investigated how protein mixture ratio and environmental pH jointly govern aggregation behavior and its subsequent impact on interfacial adsorption and emulsion stability in faba bean protein isolate (FBPI)-sodium caseinate (SC) systems. Different mixing ratios (FBPI:SC = 10:0, 7:3, 5:5, 3:7, and 0:10) were evaluated across pH 3-8 to systematically examine the relationships between bulk dispersion behavior and emulsion performance. Under neutral and alkaline conditions, formulations containing higher proportions of SC (5:5-0:10) exhibited high protein solubility (>90%), low turbidity, and strongly negative ζ-potential values (<-40 mV), indicating reduced aggregation and enhanced dispersion stability. These conditions promoted increased protein adsorption at the oil-water interface, leading to smaller and more stable emulsion droplets during storage. In contrast, acidic conditions resulted in reduced electrostatic repulsion, increased aggregation, and progressive droplet growth, indicating lower emulsion stability. Fourier transform infrared analysis suggested that these behaviors were associated with subtle changes in intermolecular interactions and interfacial organization, rather than major structural unfolding. Therefore, the results demonstrate that protein composition plays a critical role in modulating pH-dependent aggregation and interfacial behavior, which directly determines emulsion stability. This study highlights that stable emulsion systems can be achieved by suppressing aggregation and promoting interfacial adsorption, providing practical guidance for the design of high-protein beverage emulsions based on mixed plant-animal protein systems.