Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Food Science and Technology

Major Professor

Qixin Zhong

Committee Members

Faith Critzer, Jun Lin, P. Michael Davidson


Numerous delivery systems are studied for lipophilic bioactive compounds, but much work is needed for bioactive food ingredients soluble or dispersible in water. The overall hypothesis of this dissertation is that structured solid/oil/water (S/O/W) emulsions can be used to encapsulate water-soluble/dispersible ingredients to retain their release during processing and storage and control their release during simulated digestions. The encapsulation principle is to prepare spray-dried powder of water-soluble/dispersible compounds as the solid core that is coated by an oil layer emulsified by food biopolymers. The oil layer isolates the compounds from the continuous aqueous phase in emulsions to prevent the release, and the digestion of food biopolymers enables the controlled release. Glutamine was first studied as a model water-soluble compound in Chapter 2, and the S/O/W emulsion droplets with sequential protein (whey protein isolate or sodium caseinate) and citrus pectin interfacial layers minimized the release of glutamine during storage and simulated gastric digestion but gradual and complete release during simulated intestinal digestion. The solid core was substituted for spray-dried probiotic Lactobacillus salivarius NRRL B-30514 in Chapter 3, and double-layered emulsions improved the bacteria viability during storage at 4 ℃, after heating, and in vitro digestion. In Chapter 4, sugar beet pectin, a natural protein-polysaccharide conjugate, was used to prepare S/O/W emulsions, and similar improvements of bacteria viability were observed. In Chapter 5, outlet temperature, drying media, and heat adaptation were optimized to improve the viability of L. salivarius after spray drying and subsequent storage. Representative spray-dried L. salivarius samples were encapsulated in droplets emulsified with sugar beet pectin in Chapter 6. Treatments of spray-dried L. salivarius samples with a lower water activity and those with disaccharides enhanced the viability of bacteria during storage at 22ºC and 11% RH. Spray-dried lactase was studied in Chapter 7 as the last model compound. Encapsulation in S/O/W emulsions improved the preservation of lactase during thermal processing and storage to minimize lactose hydrolysis in milk, and enabled the release of lactase and hydrolysis of lactose during simulated gastric and intestinal digestions. Therefore, the studied S/O/W emulsions are significant to the production of numerous functional foods.

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