Oxidative stability of omega-3 fatty acid emulsions coted with polyelectrolyte multilayer

Abstract

In this study, we demonstrated the first preparation procedure for oil-in-water emulsion coated with tertiary and quaternary polyelectrolyte layers and their improvement on the oxidation and creaming stability of omega-3 oil-in-water emulsions. Based on the study of the optimum preparation condition, primary emulsions were prepared by homogenizing a solution of 5 %w tuna oil and 95 %w of 1.5 %w casein in water at pH 6 for 2 minutes at 20,000 rpm and 5 homogenization cycles. Surface modification of the primary emulsion by polyelectrolytes was achieved by using the layer-by-layer self assembly technique. First, the primary emulsions were further coated with either poly(diallyl dimethyl ammonium chloride) PDADMAC or chitosan (polycationic) called secondary emulsion. Then, the tertiary emulsions were prepared by coating secondary emulsion with alginate (polyanonic). Last, the quaternary emulsion coated with casein-PDADMAC-alginate-PDADMAC could be synthesized. The equivalent point for multilayer emulsion preparation was investigated by measuring %transmission and zeta potential. The mass ratios of the emulsion to polyelectrolyte at the equivalent points for the preparation of secondary emulsion were 3.2 and 3.0 for casein-PDADMAC and casein-chitosan, respectively. The mass ratios for tertiary emulsions coated with casein-PDADMAC-alginate, casein-chitosan-alginate and quaternary emulsion coated with casein-PDADMAC-alginate-PDADMAC preparations were 0.24, 0.33 and 0.77, respectively. Oxidative stability of the omega-3 in tuna oil-in-water emulsions was measured by using UV-Vis spectroscopy via ferric thiocyanate method. Physical and oxidative stability of the multilayer emulsions were found to be improved when compared with primary emulsions. The oxidative stability of all multilayer emulsions were increased around 36-38% over primary emulsion at day 4 and 5 of storage. This is because the thicker layer of multilayer emulsions and the cationic charge on the droplet of secondary and quaternary emulsion can prevent the droplet from the oxidants. The creaming stability of secondary, tertiary and quaternary emulsion was also increased around 29.78, 45.70 and 65.38% compared to the primary casein emulsion at day 7 of storage