Synergistic stabilization of high internal phase Pickering emulsions using zein nanoparticles and quillaja saponin: Advancing stability, functional properties, and fat replacement in food systems.

High internal phase Pickering emulsions (HIPPEs), stabilized by colloidal particles, have attracted interest owing to their exceptional stability, tunable viscoelasticity, and versatile encapsulation capabilities. With increasing health concerns over saturated fats and the demand for sustainable fat alternatives, novel emulsion-based substitutes are of significant interest. In this study, oil-in-water HIPPEs containing 80 % oil phase were formulated using food-grade zein nanoparticles (ZNPs) and quillaja saponin (QS) as co-stabilizers. The incorporation of QS leads to a reduction in droplet sizes, thereby modifying the physicochemical and functional properties of the emulsions. Rheological analysis reveals a concentration-dependent enhancement in gel strength accompanied by a decrease in critical strain points. A QS-to-ZNPs mass ratio of ≥1:0.5 notably enhanced thermal stability. Molecular docking further confirmed the synergistic interactions between ZNPs and QS, supporting experimental findings. The resulting optically opaque, semi-solid HIPPEs exhibit strong potential as butter substitutes in cookie formulations. Specifically, cookies formulated with HIPPEs at a ZNPs:QS mass ratio of 1:0.5 achieved partial butter replacement at levels of 25-50 %, while retaining acceptable sensory attributes. These results highlight the potential of ZNPs/QS-stabilized HIPPEs as structurally robust and functionally effective fat substitutes, offering a promising strategy for advancing sustainable and health-oriented food systems through rational colloidal design.