Effects often overlooked in lipid oxidation in oil-in-water emulsions: Agitation conditions and headspace-to-emulsion ratio

The effects of the agitation conditions and headspace-to-emulsion volume ratio on lipid oxidation in emulsions can be considerable, but have not been systematically investigated yet. In the current paper, lipid oxidation was monitored in model oil-in-water (O/W) emulsions at pH 4.0 and 25 degrees C in the presence of 200 mu M iron sulfate. The formation of primary (conjugated dienes and hydroperoxides) and secondary (p-anisidine value and TBARS) oxidation products confirmed that using rotating or shaking devices doubled the rate of oxidation product formation compared to a non-agitated system, as a result of enhanced oxygen transfer. Furthermore, we found that a higher headspace-to-emulsion volume ratio at least doubled the rate of lipid oxidation due to a higher amount of oxygen available per mass of oil, which is in agreement with the kinetics of the reaction. This indicates that the variation in literature data on lipid oxidation in emulsions can be attributed to differences in mixing conditions and volume ratios. These factors are crucial and should be reported systematically along with the agitation conditions, and sampling method. This will enable a better comparison of literature information.