Novel emulsion-based delivery systems.

Abstract

Novel emulsions with useful attributes such as improved stability, clarity and label friendliness were investigated in this thesis. Overall, this thesis has three parts: the first part systematically studied the formation and optical properties of nanoemulsions; the second part focused on formation and beverage cloud application of multilayer emulsions; and the third part evaluated the formation, stability and beverage cloud application of multiple phase emulsions. In part 1, nanoemulsions were prepared using four different food grade biopolymers (different concentrations) and high pressure homogenization (Microfluidizer®, different pressures, temperature and number of passes). It was found that increasing number of passes through the microfluidizer led to a wider particle size distribution. The effect of oil types on mean droplet diameter (MDD) was complex being dependent on the emulsifier, homogenization pressure, phase viscosity and number of passes. It was also found that interface composition, relative refractive index, volume fraction of dispersed phase and droplet size influenced the turbidity. A polynomial relationship was found between MDD and turbidity within the MDD range of 80 to 400 nm. The effects of lipid phase and interface composition on turbidity were droplet size dependent. A linear relationship between volume fraction of dispersed phase and turbidity was established. Experiment results demonstrated that matching refractive indices between phases led to clear emulsions. Finally the primary destabilization mechanism of MCT nanoemulsions emulsified with modified starch was identified as coalescence from a two-week shelf life study. In part 2 of this thesis, the ability to prepare secondary and tertiary beverage cloud emulsions using a layer-by-layer deposition technique was developed. Proteins, β-lactoglobulin (L) and sodium caseinate (S), were selected to stabilize the primary emulsions. Biopolymers of sodium alginate (S), ι-carrageenan (C), gum Arabic (G), pectin (P), chitosan (Ch) and gelatin (Ge) were evaluated as secondary and tertiary layers. Biopolymer concentration and pH were found critical to the formation of stable multilayer emulsions. Protein and polysaccharide type also impacted droplet size and δ-potential of multilayer emulsions. Interestingly, β-lactoglobulin was found better than sodium caseinate in forming protein-polysaccharide interfacial complexes as demonstrated by smaller MDD of LA, LP and LC than those of SA, SP and SC. It was also found biopolymer concentration has to be above a critical value (0.2 ~ 0.5% w/w) to prevent multilayer emulsions from bridging flocculation. Our data showed that both secondary (LA, LC, LG) and tertiary (LGC) emulsions formed by electrostatic deposition could provide the same performance as traditional emulsifiers of gum Arabic (G) and modified starch (M). After four weeks of storage at room temperature, beverage clouds stabilized with G, M, LA, LC, LG and LGCh showed MDDs of 0.68, 0.67, 0.90, 0.82, 0.65 and 2.2 μm, respectively, and turbidity losses of 18, 28, 22, 19, 25 and 17%, respectively. In part 3 of this thesis, water-in-oil-in-water emulsions (W/O/W, also called double emulsions) were studied using a concentrated sucrose solution as a natural weighing agent to increase the density of the oil phase. The results indicated that MDD of W/O emulsions decreased with increasing emulsifier (polyglycerol polyricinoleate, PGPR) concentration. Homogenization pressure and number of passes through a microfluidizer affected MDD, size distribution and encapsulation efficiency (EE) of yellow #6 (included in the water phase as a marker to measure EE). The hydrophilic emulsifier type and oil phase showed great impacts on EE and stability of the W/O/W emulsions. A high EE (>85%) was achieved in gum acacia (GA) stabilized double emulsions whereas Tween 20 and modified starch (MS) stabilized double emulsions showed low EE (< 50%) demonstrating that the type of hydrophilic emulsifier is a critical factor governing stability of double emulsions. Gelling the inner aqueous phase proved to be ineffective in improving EE and stabilizing double emulsion in this study. Results on beverage cloud applications of W/O/W emulsions indicated that GA stabilized emulsions are more stable to turbidity loss and ring formation than those stabilized by MS. Beverage clouds containing OT-based W/O/W emulsions without gelling the inner phase showed low turbidity loss during shelf-life without ring formation demonstrating potential commercial value of these emulsions.