|M.Sc Student||Ruiz-Rodriguez Paulina|
|Subject||Characterization of Pickering O/W Emulsions Stabilized|
by Silica Nanoparticle and their Responsiveness
to in Vitro Digestion Conditions
|Department||Department of Biotechnology and Food Engineering||Supervisor||Professor Uri Lesmes|
|Full Thesis text|
Emulsions stabilized by particles, known as Pickering emulsions have been the subject of recent studies, given their exceptional stability and suitability for various pharmaceutical and food applications. Particularly emulsions stabilized by silica nano-particles (NPs) 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, the focus of this work is to produce and characterize silica-stabilized emulsions and their potential digestive fate. The main hypothesis was that the unique barrier properties provided by silica nano-particles enhance emulsion stability to physiological processes occurring namely at droplet interfaces. Particularly, such emulsions are expected to exhibit improved stability to ionic strength, enzymatic activity and other conditions of the upper human gastrointestinal tract (GIT).
To this end, emulsions with 0.5-5% (w/w) silica NPs were produced to study the effect of particle concentration on size, electrokinetic potential, comparative stability, appearance and viscosity. Further, former emulsions were subjected to the action of artificial saliva, NaCl (0-200mM), varying pH (3<pH<7), bile (0-25mg/mL) and duodenal lipolysis, in order to evaluate their digestive fate.
Measurements indicate that increasing particle concentration above 1% (w/w) silica leads to the formation of more stable emulsions and smaller droplet size, without having a marked effect on droplet charge. It was also found that these emulsions exhibit shear thinning behavior and an unexpected tendency to sediment rather than to cream. Further, emulsions showed phenomena atypical to common simple emulsions; for example, stability of 1% (w/w) silica-stabilized emulsions increased with increasing levels of NaCl, and above 150mM NaCl, reverted emulsion separation from sedimentation to creaming. Additionally, simulated intestinal lipolysis in a pH-stat model revealed that silica nano-particles reduce the extent of emulsion lipolysis compared to an emulsion stabilized by β-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.