Characterization of Pickering O/W Emulsions Stabilized by Silica Nanoparticles and Their Responsiveness to In vitro Digestion Conditions

Emulsions stabilized by particles, known as Pickering emulsions, show exceptional stability, making them suitable for various applications. Particularly, emulsions stabilized by silica have been considered and intended for various cosmetic, food and pharmaceutical applications. However, growing concerns regarding the safety of nano-sized colloids raise the need to evaluate their safety and their possible digestive fate. Therefore, this work aimed to study the properties of silica-stabilized emulsions made with 0.5-5 % (w/w) silica nano-particles and elucidate emulsion behavior under different conditions of the human gastrointestinal tract (GIT). Size, electrokinetic potential, comparative stability, appearance and viscosity measurements indicate exceeding 1 % (w/w) silica yields highly stable emulsions with shear thinning behavior and an unexpected tendency to sediment rather than to cream. Further, emulsions subjected to the action of artificial saliva, NaCl (0–200 mM), varying pH (3 < pH < 7) and bile (0–25 mg/mL) showed phenomena atypical to common simple emulsions. For example, the stability of 1 % (w/w) silica-stabilized emulsions increased with increasing levels of NaCl, and above 150 mM NaCl emulsion separation was reverted from sedimentation to creaming. Additionally, simulated intestinal lipolysis in a pH stat model revealed silica nano-particles reduce the extent of emulsion lipolysis compared to an emulsion stabilized by beta-lactoglobulin. Overall, the study's findings show that the unique properties of silica-stabilized emulsions offer not only exceptional physical stability but also the possibility to alter emulsion digestive fate; all are suggested to stem from particle-particle interactions which play an elemental role in the macroscopic stability of emulsions and offer another pathway to rationally design emulsions for oral applications.