Thesis (M.Sc.)--Chulalongkorn University, 2011

The aim of this study is to retard the oxidation of unsaturated fatty acid in tuna oil-in-water emulsion by preparing as multilayer emulsion and adding antioxidants. The multilayer tuna oil-in-water emulsions were prepared using layer-by-layer technique. The primary emulsion was prepared by homogenizing 5 %w/v tuna oil, 0.4 %w/v WPI in 100 mM acetic-acetate buffer solution as emulsifier. The secondary and tertiary emulsions were prepared by coating the oil droplets with the charged biopolymers. Chitosan, a cationic polyelectrolyte, and alginate and carrageenan, anionic polyelectrolytes, were selected. The pH of emulsifier was controlled at either pH 3.5 and 6.0. The physical characteristic and physical stability was investigated by measuring the creaming index, % transmission, particle size and zeta potential. The particle size of emulsions increased, while the creaming index and % transmission were improved when increasing the number of layers around emulsion. The physical stability of tertiary emulsions was improved comparing to the primary and secondary emulsions for both pH conditions. The oxidative stability of emulsions was investigated via the ferric thiocyanate method by using UV-Vis spectroscopy. After storage, all emulsions released lipid hydroperoxide. We found that the secondary and tertiary emulsions decreased the oxidation reaction comparing to the primary emulsion. Thus, the multilayer emulsions could be improved the stability of tuna oil-in-water emulsion. The effect of antioxidants, sesame oil, capsaicin oleoresin, genistein and roselle extract on the decrease in the oxidation rate of primary emulsion were investigated. Sesame oil and capsaicin oleoresin were added directly in tuna oil, which we found that added 0.5 %w/v capsaicin oleoresin the better oxidative stability. While genistein and roselle extract were added directly in emulsifier solutions, we found that the 200 ppm roselle extract could improve the oxidative and physical stabilities.