The effect of interfacial microstructure on the lipid oxidation stability of oil-in-water emulsions.

A novel approach to reduce lipid oxidation in oil-in-water emulsions has been taken and involves the manipulation of the emulsions' interfacial microstructure. Oil-in-water emulsions stabilised by sodium caseinate (CAS), Tween 20 and silica particles were prepared and their lipid oxidation stability was assessed over a week. Lipid oxidation was monitored by measuring the concentration of primary lipid oxidation product, using the peroxide value method and secondary lipid oxidation products formation were evaluated with the p-anisidine technique. Oil-phase volume fraction and emulsifier type both play key roles in influencing the rate of lipid oxidation. Decreasing the oil fraction from 30% to 5% was found to promote lipid oxidation as a result of an increase in the amount of pro-oxidant iron per gram of oil. It was further shown that, CAS in the continuous phase reduces lipid oxidation at pH 7 due to its metal chelating ability. In addition, the results show that, emulsions stabilised with silica particles (at pH 2) inhibit lipid oxidation to a greater extent than emulsions stabilised with surfactants alone. The present study demonstrates that emulsions' physical properties such as oil-phase volume fraction, droplet size and droplet interfacial microstructure are all formulation parameters that can be used to significantly reduce the rate of lipid oxidation.