The use of natural antioxidants to combat lipid oxidation in O/W emulsions

This research investigated the efficacy of four natural antioxidants, quercetin, curcumin, rutin hydrate and ascorbic acid in their ability to combat Lipid Oxidation (LO) within different oil-in-water (O/W) emulsion environments. The free radical scavenging and metal chelating ability of the four antioxidants was first assessed through DPPH and Ferrozine assays respectively and used to help explain each antioxidants efficacy in particular environments. Generally, in emulsions with no added iron, compounds that exhibited the greatest levels of DPPH and Ferrozine inhibition provided the best oxidative stability. In the presence of added iron, antioxidant effectiveness reduced dramatically and in some cases resulted in prooxidant activity. It was concluded that the antioxidant metal chelating mechanism of antioxidants in emulsions with added iron was largely insignificant compared to the prooxidant effect gained by these compounds through their interaction with iron. The most non-polar compounds, curcumin and quercetin provided peroxide value (PV) reductions of 65% and 74% respectively in 5% oil phase volume emulsions compared to just 28% and 43% PV reductions in 40% oil phase volume emulsions; thus providing more evidence of the widely reported 'polar paradox'. Combinations of ascorbic acid with quercetin or curcumin resulted in antioxidant synergism, whereas other antioxidant combinations led only to additive or antagonistic effects. This research builds on the understanding of the fundamental behaviour of natural antioxidants within different emulsion formulations.