Design and fabrication of functional lipid nanoparticles based on control of interfacial properties using biopolymers

The main objective of this research was to better understand the formation, stability and properties of emulsions having lipid nanoparticles with tunable functional properties by controlling the composition and structure of the biopolymer interface, in order to develop better food-grade delivery systems. Initially, the influence of environmental stresses (pH, heating and salts) on the physicochemical properties of cationic lactoferrin (LF)-stabilized oil-in-water emulsions was investigated. At ambient temperature, the emulsions were found to be stable at all times except when pH was close to pI. When LF-coated droplets were heated in distilled water, and then their pH was adjusted in the range 2 to 9, they were highly unstable to aggregation at pH 7 and 8. These results have important implications for the formulation and production of emulsion-based products using lactoferrin as an emulsifier. Next, we studied the properties and stability of multilayer emulsions formed using the primary emulsifier lactoferrin and secondary polysaccharides like low methoxyl pectin (LMP), high methoxyl pectin (HMP) and alginate. At neutral pH, electrostatic attractions occurred between the anionic groups on the polysaccharide molecules and the cationic patches on the protein surfaces. In the absence of polysaccharide, the LF-coated droplets were highly unstable to aggregation when heated above about 60 ºC at pH 7, presumably because thermal denaturation of the adsorbed proteins increased droplet attraction. Changes in the physicochemical properties and digestibility of both the primary LF and the secondary LF-polysaccharide emulsions, under simulated gastrointestinal conditions were monitored. The presence of a dietary fiber coating around the initial lipid droplets had little influence on the total extent of lipid digestion in simulated intestinal fluid (SIF), but LF-alginate emulsions had a slower initial digestion rate than the other emulsions. These results suggest that the dietary fiber coatings may become detached in the small intestine, or that they were permeable to digestive enzymes. Pepsin was found to have little influence on the physical stability or digestibility of the emulsions. Next, we fabricated emulsions with oil droplets coated by sequential electrostatic deposition of cationic LF and anionic β-lactoglobulin (BLG) at pH 6.5: LF, LF-BLG, LF-BLG-LF, and LF-BLG-LF-BLG. Changes in the physicochemical properties of these systems were characterized when they were exposed to environmental stresses and simulated small intestine conditions. LF-coated droplets were stable throughout the entire pH range which was attributed to strong steric repulsion. All the nanolaminated droplets were unstable to aggregation at pH 5, which is between the isoelectric points of BLG and LF. Finally, a premix approach was utilized to fabricate interfacial coatings around the lipid droplets, instead of the LbL approach. This method involved mixing BLG and LF prior to emulsion formation and the influence of environmental stresses on the properties of these emulsions was examined. Droplets coated by BLG were unstable to aggregation near their isoelectric point (pH ≈ 5), whereas those coated by LF were stable across the whole pH range. The stability of emulsions to pH induced aggregation improved as the ratio of LF-to-BLG in the mixed systems was increased. Lipid droplets coated by either LF or BLG were unstable to aggregation at high salt concentrations (500 mM NaCl, pH 6.5), but those stabilized by mixed protein coatings (LF and BLG) were stable, which was attributed to an increase in interfacial thickness and steric repulsion. Droplets coated by BLG were stable to droplet aggregation after thermal treatment (30 to 90 oC, 0 mM, NaCl pH 7), whereas those coated by LF were highly unstable when heated above their thermal denaturation temperature. The thermal stability of the droplets decreased as the amount of LF in the mixed systems increased. (Abstract shortened by UMI.