DEVELOPMENT OF ΒETA-LACTOGLOBULIN BASED PARTICLES AS COLLOIDAL STABILIZERS AND EVALUATION OF THEIR PERFORMANCE ON INTERFACES

Abstract

Beta-lactoglobulin (Blg) is a major whey protein in bovine milk. The desirable functional properties of Blg make it a versatile material, which has been processed into various types of colloidal systems such as nanoparticles, microgels and emulsions. This dissertation first developed several stable colloidal systems using native Blg molecules or denatured Blg aggregates as stabilizers. The study then elucidated the stabilization mechanism by characterizing Blg microgels adsorption on the interface.

Firstly, novel selenium nanoparticles were developed using Blg as a stabilizer. The synthesized Blg-selenium nanoparticles were stable at pH 2.5-3.5 and 6.5-8.5 at 4ºC for 30 days as a result of electrostatic repulsions. Furthermore, the cell toxicity of selenium nanoparticles was significantly lower than that of sodium selenite on both cancerous and non-cancerous cells, implying their potential uses as anti-cancer medicines.

The second part of this study was to stabilize a novel water-in-water (W/W) emulsion system using self-assembled Blg microgels. The microstructure and stability of the W/W emulsion were investigated under different environmental conditions. Microgels accumulating at the liquid-liquid interface led to a stable emulsion at pH 3 to 5. When pH was increased above the pI of the microgels, the emulsion was destabilized because the microgels tended to stay in the continuous phase (i.e., dextran) rather than the interface. In addition to electrostatic interactions, interfacial tension and hydrophobic attraction between microgels and two polymer phases were investigated to better understand the driving force for particles’ accumulation at the interface.

Lastly, we proposed a new method to study the interfacial properties of Blg microgel. Quartz crystal microbalance with dissipation (QCM-D) was employed to investigate adsorption behavior of Blg microgels on a hydrophobic solid surface, which was hypothesized to mimic the oil-water interface. Coupling with atomic force microscopy (AFM), QCM-D showed the ability to characterize the microgels adsorption efficiency and viscoelasticity of adsorbed layer on the solid surface. The application of QCM-D and AFM enabled us to generate insights into the fundamental behavior of soft particles at a solid-liquid interface.