Stability mechanism of Pickering emulsions co-stabilized by protein nanoparticles and small molecular emulsifiers by two-step emulsification with different adding sequences: From microscopic to macroscopic scales

Pickering emulsions are increasingly being explored for their potential applications within the food industry. However, the stability of these emulsions is often limited when stabilized by single colloidal particles. Herein, we examined the possibility of improving the performance of Pickering emulsions by using a combination of colloidal particles (zein nanoparticles, Z) and small molecular emulsifiers (quillaja saponin, Q). The stability mechanism of Pickering emulsions was explored from microscopic to macroscopic scales using QCM-D, microrheology, and Cyro-SEM, et. Corn oil-in-water Pickering emulsions were prepared by adding the Z and Q in different sequences: (i) mix Z and Q and then homogenize (“ZQ-P”); (ii) add Z, homogenize, and then add Q (“Z-QP”); (iii) add Q, homogenize, and then add Z (“Q-ZP”). The sequence significantly influenced the interfacial structure and properties of Pickering emulsions. Macroscopic rheology and microrheology showed that the Pickering emulsions formed an elastic-like structure (G′>G″) and their viscoelastic properties increased over time. QCM-D analysis showed that the properties of the interfacial layers depended on the emulsifier addition sequence used to form the Pickering emulsions. The interfacial membranes formed using the Q-ZP sequence were the thickest (5.8 nm). Cyro-SEM imaging showed that nanoparticle bridges formed between neighboring droplet surfaces, which led to the formation of a 3D network that provided mechanical strength. Overall, this study showed that the Q-ZP addition sequence was the most effective at forming stable Pickering emulsions. It provides new insights that may facilitate the formation of plant-based Pickering emulsions with improved functional performance in food applications.