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Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Food Science

Year Degree Awarded

Spring 2015

First Advisor

David Julian McClements

Subject Categories

Food Chemistry

Abstract

The objective of this thesis was to design and develop novel food-grade nanoemulsion-based delivery systems for the encapsulation, protection and delivery of lipophilic bioactive food components. These delivery systems could be widely applied in aqueous-based fortified food products, such as beverages, salad dressing and yogurt etc.

Both the low- and high-energy methods could be used for fabricating nanoemulsions (r < 100 nm). The microfluidization method could form nanoemulsions at low surfactant-to-oil ratios (SOR < 0.1), but it required the use of high-energy inputs and expensive equipment. On the other hand, the spontaneous emulsification method could also form ultrafine emulsions and moreover it was simple and inexpensive, but it required much higher surfactant-to-oil ratios (SOR > 0.5) for forming nanoemulsions.

Q-Naturale® is a natural food-grade surfactant, which is got from the bark of the Quillaja saponaria Molina tree. By using high pressure homogenization (microfluidization), Q-Naturale® could form relatively small droplets (d < 200 nm) at low surfactant-to-oil ratios (SOR < 0.1), but the droplets were not as small as those produced using Tween 80 under similar conditions (d < 150 nm). The emulsions formed by using Q-Naturale® as the emulsifier were stable to droplet coalescence over a range of pH values (2 to 8), salt concentrations (0 to 500 mM NaCl) and temperatures (20 to 90 ºC). Thus, the design of “all-natural” delivery system for vitamin E by using Q-Naturale® as the emulsifier were then studied. Ultrafine emulsions could not be fabricated using pure α-tocopherol acetate as the oil phase due to its very high viscosity, but they could be formed when ≥ 20% MCT was incorporated into the oil phase prior to homogenization. In the absence of glycerol, Q-Naturale® was able to form emulsions containing relatively small droplets (d < 400 nm) from oil phases containing relatively high vitamin levels (60 to 80%). The addition of glycerol into the aqueous phase could help decreasing this droplet size. Q-Naturale® was more effective than Tween 80 at producing small droplets with oil phase containing high levels of vitamin E acetate.

The influence of carrier oil type on the bioaccessibility and molecular form of vitamin E encapsulated in Q-Naturale® delivery system was then examined using a simulated gastrointestinal model. The total bioaccessibility of vitamin E after digestion was higher for LCT- than MCT-emulsions, which was attributed to the greater solubilization capacity of mixed micelles formed from long chain fatty acids. The conversion of α-tocopherol acetate to α-tocopherol after in vitro digestion was also considerably higher for LCT- than MCT-emulsions, which may impact the subsequent absorption of the vitamin E. Morever, by using emulsion titration assay for further quantifying the kinetics and extent of vitamin E and vitamin E acetate solubilization in model mixed micelles, the solubilization capacities were depended on the composition of the mixed micelles: micelle solubilization of vitamin E was increased by the presence of phospholipid (DOPC), but did not depend strongly on the presence of free fatty acid (octanoic acid or linoleic acid). The solubilization capacity of the mixed micelles for vitamin E was higher than that for vitamin E acetate, which was attributed to differences in the ability of the vitamin molecules to be incorporated into the micelle structure.

Finally, all the key factors impacting on the bioaccessibility of emulsified vitamin E, such as calcium ions, phospholipids, carrier oil type etc., were then overall studied using a simulated small intestine model. The addition of calcium (CaCl2) to the SSIF increased the extent of lipid digestion in LCT-emulsions, but had little impact in MCT-emulsions. The bioaccessibility of vitamin E increased in the presence of calcium and phospholipids (DOPC) in LCT-emulsions, but decreased in MCT-emulsions. The highest bioaccessibility (≈ 66%) was achieved for LCT-emulsions when the SSIF contained both calcium and DOPC. The conversion of α-tocopherol acetate to α-tocopherol after in vitro digestion was considerably higher for LCT-emulsions when calcium ions were present in the SSIF, but was not strongly affected by SSIF composition for MCT-emulsions.

Overall, the results obtained in these studies will provide guidelines for rationally designing effective nanoemulsion-based delivery systems for encapsulating, protecting and delivering lipophilic bioactive components. These delivery systems could be used in various industrial products, such as fortified foods, pharmaceuticals, cosmetics, and personal care products in the future.

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