Date of Award

12-2011

Degree Type

Thesis

Degree Name

Master of Science

Major

Food Science and Technology

Major Professor

Qixin Zhong

Committee Members

Federico Harte, John Mount

Abstract

Fish oil has abundant polyunsaturated fatty acids that are important to health but are oxidized easily during shelf-life storage. Engineering oil/water interfaces of emulsions has been studied extensively, but practical technologies are still demanded by the food industry. Whey proteins aggregate during heating, and the preheated whey protein/aggregate may increase the robustness of interfaces and in turn improve oxidative and physical stability of fish oil emulsions. In this study, whey protein isolate (WPI) solutions were prepared at 0-100 mM NaCl and pH 7.0 and preheated at 85 °C for 5-30 min. The preheated WPI was used to prepare fish oil emulsions that were evaluated for oxidative stability, droplet size, and zeta-potential during storage at 37 °C and 33.3% relative humidity for 35 days. The emulsions were also spray-dried for evaluation of oxidative stability of powdered products, which were also reconstituted for assessment of physical and oxidative stability. Further, because maltodextrins (MD) improve spray drying performance, emulsions were prepared at WPI:MD mass ratios of 1:2, 1:4, and 1:8. The best oxidative stability for both liquid and spray-dried emulsions was observed for emulsions prepared with WPI preheated at an intermediate NaCl concentration (25 mM), WPI:MD mass ratio (1:4), and heating time (15 min). For these emulsions, the highest extent of lipid oxidation was observed at day 20, with more significant reduction in lipid hydroperoxide (121.55 mEq/kg oil) and less in thiobarbituric-acid-reactive-substances - TBARS (7.10 mmol/kg oil) when compared to bulk fish oil (lipid hydroperoxide of 220.91 mEq/kg oil and TBARS of 8.55 mmol/kg oil). Emulsions prepared with preheated WPI had bigger droplets with less negative zeta-potential that changed more significantly during storage. . Our work demonstrated an efficient approach to improve oxidative stability of fish oil, but much work is needed to improve both physical and oxidative stability of emulsions.

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