Fabrication of complex interface and pH-switchable Pickering emulsions prepared by electrostatic associative of zein nanoparticles with QS-coated nanodroplets

Edible soft nanoparticles have received increasing interest in alternating to surfactants as stabilizers of food-grade emulsions. Here, we describe a novel approach to fabricate pH-switchable Pickering emulsions in which electrostatic heteroaggregation of oppositely charged soft nanoparticles at the oil-water interface. Taking advantage of the electrostatic attraction-driven coacervation of positively charged Zein nanoparticles (ZNPs) and negatively charged QS-coated nanodroplets (SNDs) as well as the controllable wettability, the ZNPs/SNDs associative colloidal particles (ZSPs) are coacervated to form a complex viscoelastic film at the oil-water interface, enabling Pickering stabilization of the emulsion. The oil-in-water Pickering emulsion stabilized by ZNPs associatived with SNDs is stable over 30 days storage, in contrast to those emulsions stabilized by ZNPs solely. The resulting Pickering emulsions are also form a gel-like structure and show shear thinning behavior, and these properties were adjustable by manipulating their concentration and proportion. Moreover, the emulsions are sensitive to pH variations, that stable Pickering emulsion achieved at acidic pH's (pH ∼4) while at the neutral, the emulsion separates into emulsion and serum phases due to flocculation. The Pickering emulsion can be reversibly switched by pH, which probably from the pH-controlled electrostatic attraction between ZNPs and SNDs. The finding demonstrates a newly strategy of preparing pH-switchability Pickering emulsions, with potential applications in the fields of foods, cosmetics, and drug delivery.