Improving whey protein foam stability via soluble complexation with low methoxyl pectin above the isoelectric point: Mechanisms and angel food cake application

Whey protein isolate (WPI) is widely recognized for its excellent foamability; however, its application in food systems is limited by poor foam stability. This study investigated the foaming properties of heated soluble complexes (HCPX) formed by heating WPI (4% wt/wt) with low methoxyl pectin (LMP, 0-0.5% wt/wt)-at pH 5.6, 6.0, and 6.2 (above the isoelectric point of WPI, pI ≈5.2), and evaluated their functional performance in a model angel food cake system prepared with whey protein concentrate (WPC). Characterization of the complexes revealed that HCPX formation resulted in smaller aggregate sizes, increased negative surface charge, and altered bulk rheological properties relative to heated WPI alone. Zeta-potential measurements indicated that electrostatic interactions between WPI and LMP reached saturation at 0.3% LMP, regardless of the pH at which complexes were formed. Increasing LMP concentration elevated solution viscosity and enhanced shear-thinning behavior, with the most pronounced effects observed at pH 5.6. Despite these rheological changes, HCPX formation had no significant effect on initial or equilibrium surface tension, and foam overrun was maintained across all conditions. Foam stability, however, was dramatically improved in all HCPX systems compared with heated WPI, with complete drainage resistance observed at LMP concentrations of ≥0.2% at pH 6.2. Confocal laser scanning microscopy (CLSM) confirmed reduced coalescence and disproportionation in HCPX foams,-consistent with improved foam stability through increased bulk-phase viscosity and enhanced foam lamellae rheology. The enhanced foam stability is attributed to a combination of increased bulk-phase viscosity and strengthened foam lamellae rheological properties. These functional improvements were successfully translated to an applied baking system, where partial replacement of WPC with HCPX yielded angel food cakes with greater volume, lower density, and finer crumb texture. These findings demonstrate that WPI-LMP complexation under optimized conditions is an effective strategy for improving whey protein foam stability with direct relevance to food manufacturing applications.