Oxidative stability of water/oil mixtures as influenced by the addition of free Cu2+ or Cu–alginate gel beads

The formation of Cu–alginate complexes and the impact of free or bound copper on the oxidative stability of model water/oil mixtures containing edible sunflower or corn oil were examined. Equilibrium dialysis showed that copper binding capacity of alginate increased proportionally with copper concentration and the binding was rapid. The results indicated that 25 mM CuCl2 was necessary in obtaining beads of spherical shape and adequate mechanical strength (0.45 N at 80% compression) to avoid rupture during mixing, whereas lower CuCl2 concentrations resulted in weak gel beads (0.34 N) of irregular shape. When Cu–alginate beads were dispersed in the aqueous phase to give 0.5 mM copper, the peroxide value of water/corn oil mixtures was 3.7 mEq peroxide/kg oil after 7 days. Corn oil-containing mixtures with 0.5 mM free Cu2+ in the aqueous phase had a peroxide value ∼3 times higher (P < 0.001) after the same storage time. However, copper binding by alginate did not significantly reduce the peroxide values of the water/sunflower oil mixtures. Results indicated that the binding of pro-oxidant minerals, such as copper, in alginate beads can reduce the levels of oxidation in water/oil mixtures.