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Date of Award

5-2013

Document Type

Campus Access

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

First Advisor

D. Julian McClements

Second Advisor

Hang Xiao

Third Advisor

Sam R. Nugen

Subject Categories

Agriculture | Food Science | Nanoscience and Nanotechnology

Abstract

There is growing interest in the use of nanoemulsions as delivery systems for lipophilic functional agents in food and beverage products due to their high optical clarity, physical stability and bioavailability. The goal of this research is to establish quantitative structure-function relationships to allow rational formulation of food-grade nanoemulsions for food and beverage applications.

Initially, formation of oil-in-water nanoemulsions using a low energy method was examined. Nanoemulsions were formed using the phase inversion temperature (PIT) method, which involves heating a surfactant, oil, water (SOW) systems near the PIT, and then cooling rapidly with stirring. Preliminary experiments were carried out using a model system consisting of a non-ionic surfactant (C 12 E4 ), hydrocarbon oil (tetradecane), and water. Nanoemulsions were formed by holding SOW mixtures near their PIT (38.5 °C) and then cooling them rapidly to 10 °C. The PIT was measured using electrical, conductivity and turbidity methods. The optimum storage temperature for PIT-nanoemulsions was about 27 °C lower than the PIT. The stability of PIT-nanoemulsions at ambient temperatures can be improved by adding either Tween 80 (0.2 wt%) or SDS (0.1 wt%) to displace the C 12 E4 (Brij 30) from the nano-droplet surfaces.

Experiments were then carried out to establish if stable nanoemulsions could be formed using the PIT method from food-grade ingredients. Nanoemulsions were fabricated from a non-ionic surfactant (Tween 80) and flavor oil (lemon oil) by heat treatment. Different types of colloidal dispersion could be formed by simple heat treatment (90 °C, 30 minutes) depending on the surfactant-to-oil ratio (SOR): emulsions at SOR < 1; nanoemulsions at 1 < SOR < 2; microemulsions at SOR > 2. The results suggested that there was a kinetic energy barrier in the SOW system at ambient temperature that prevented it from moving from a highly unstable system into a nanoemulsion system. The conditions where stable nanoemulsions could be fabricated were also established when sucrose monopalmitate (SMP) and lemon oil were used as the surfactant and oil phase. Nanoemulsions ( r < 100 nm) were formed at low surfactant-to-oil ratios (SOR < 1) depending on homogenization conditions, whereas microemulsions (r < 10 nm) were formed at higher ratios (SOR > 1). Relatively stable nanoemulsions could be formed at pH 6 and 7, but extensive particle growth/aggregation occurred at lower and higher pH values.

Flavor oil nanoemulsions were also formed using an emulsion titration method that involves titration of emulsion droplets into surfactant micelle solutions. In this study, the effectiveness of nanoemulsion formation using nonionic surfactants (sucrose monopalmitate (SMP) and/or Tween 80 (T80) was investigated. Lemon oil was transferred from emulsion droplets into the micelle phase until a critical lemon oil concentration ( Csat ) was reached. The solubilization process was rapid (< few minutes), with the rate increasing with increasing surfactant concentration. The value of Csat increased with increasing surfactant concentration and was higher for SMP than Tween 80.

The influence of lemon oil composition (1×, 3×, 5×, and 10×) on the formation and properties of oil-in-water nanoemulsions was also studied. Initially, the composition, molecular characteristics, and physicochemical properties of four lemon oils were established. The main constituents in 1-fold lemon oil were monoterpenes (> 90 %), whereas the major constituents in 10-fold lemon oil were monoterpenes ([approximate] 35%), sesquiterpenes ([approximate] 14%) and oxygenates ([approximate] 33%). The density, interfacial tension, viscosity, and refractive index of the lemon oils increased as the oil fold increased ( i.e. , 1× < 3× < 5× < 10×). The stability of oil-in-water nanoemulsions produced by high pressure homogenization was strongly influenced by lemon oil composition. The lower fold oils were highly unstable to droplet growth during storage (1×, 3×, 5×) with the growth rate increasing with increasing storage temperature and decreasing oil fold. Oil fold also affected the solubilization and stability of lemon oil nanoemulsions titrated into a non-ionic surfactant (Tween 80) solution. The movement of oil molecules from nanoemulsion droplets to surfactant micelles increased with increasing lemon oil fold.

Finally, nanoemulsions were used as delivery systems for β-carotene, a bioactive lipophilic component. The influence of carrier oil composition (ratio of digestible to indigestible oil) on the physical stability, microstructure, and bioaccessibility of β-carotene nanoemulsions was investigated using a simulated gastrointestinal tract model. The extent of free fatty acid production in the small intestine increased as the amount of digestible oil in the droplets increased. The bioaccessibility of β-carotene also increased with increasing digestible oil content, ranging from [approximate] 5% for the pure lemon oil system to [approximate] 76% for the pure corn oil system.

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