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 25mM CuCl₂ was necessary in obtaining beads of spherical shape and adequate mechanical strength (0.45N at 80% compression) to avoid rupture during mixing, whereas lower CuCl₂ concentrations resulted in weak gel beads (0.34N) of irregular shape. When Cu-alginate beads were dispersed in the aqueous phase to give 0.5mM copper, the peroxide value of water/corn oil mixtures was 3.7mEq peroxide/kg oil after 7days. Corn oil-containing mixtures with 0.5mM 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.