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

Lipid oxidation was monitored by measuring the concentration of primary lipid oxidation product, using the peroxide value method. Increasing silica particles concentration at the interface, results in decrease in the rate of lipid oxidation due to ability of silica particles to form a thick interfacial layer around droplets. ► O/W emulsions stabilised by sodium caseinate, Tween 20 and silica particles. ► Lipid oxidation rate was monitored over extended time. ► Silica particles at the interface are able to reduce the lipid oxidation rate. ► CAS can reduce the rate of oxidation through its ability to scavenge free radicals. 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.