Emulsion droplet interfacial engineering to improve the stability of omega -3 fatty acids and citrus oils
Lipids such as omega-3 fatty acids and citrus oils are important food components due to their nutritional and flavor benefits, respectively. Both of these food lipids are susceptible to chemical degradation resulting in formation of unacceptable off-flavors, nutrient and flavor loss. Oil-in-water emulsions could be used as an effective tool to protect these chemically sensitive lipids from deterioration by engineering the emulsion droplet interfacial membrane (e.g. charge and/or thickness) using proteins or multiple layers of emulsifiers. The objective of this study was to investigate the effectiveness of the interfacial characteristics of emulsions stabilized with proteins or multiple layers of emulsifiers in preventing oxidative deterioration of omega-3 fatty acids and citrus oil flavor compounds.
Factors influencing the stability of protein-stabilized oil-in-water emulsions at pH 3.0 were examined. Physical instability of whey protein isolate (WPI)-stabilized corn oil-in-water emulsions increased considerably after thermal processing at ≥ 70°C in the presence of ≥ 150 mM NaCl. WPI-stabilized oil-in-water emulsions containing 25 wt% algal or menhaden oils at pH 3.0 had good oxidative stability when pasteurized and stored at 4°C. The addition of EDTA and mixed tocopherol isomers further increased oxidative stability. These results suggest that WPI-stabilized algal or menhaden oil-in-water emulsions at pH 3.0 containing EDTA may be used as an ingredient delivery system to incorporate ω-3 fatty acids into functional foods.
Citral/hexadecane- or limonene/hexadecane-in-water emulsions were prepared with varying interfacial properties by coating the oil droplets with WPI, sodium dodecyl sulfate (SDS), SDS-chitosan or gum arabic (GA). Emulsifier type had little influence on the rate of citral degradation. However, WPI and SDS-chitosan were more effective at retarding the oxidation of citral degradation products and limonene in comparison to emulsions stabilized by GA. Inhibition of oxidation by the WPI or SDS-chitosan systems could be due to the ability of these emulsifiers to produce cationic emulsion droplet interfacial membranes that inhibit the interactions between dispersed lipids and continuous phase prooxidants such as iron. This research may lead to development of new strategies to improve the stability of emulsified products containing citrus oils.