Oxidative stability of iron enriched oil –in-water emulsions

Abstract

In the present work the oxidative stability of sunflower oil-in-water emulsions has been researched on. Proteins can prevent or promote lipid oxidation by various mechanisms depending on their physicochemical characteristics. Sodium caseinate (NaCas) can prevent lipid oxidation, essentially by chelating metals ions, but other mechanisms such as free-radical scavenging may also be involved. Conjugated dienes (CD) were evaluated (primary products of lipid oxidation), and the volatile compounds: pentane, hexanal, 1-octen-3-ol, and 2-(E)-octenal were selected as markers of secondary products of lipid oxidation (GC/SPME). The affinity of milk proteins to bind free iron ion is the first factor that controls the transfer to oil/water interface. All the soluble iron that could be present in the emulsions was likely bound by caseins At pH = 6.5, the oxidative stability of NaCas-stabilized emulsions greatly depends on metal availability. The chelating properties of NaCas and electrostatic interactions favored positioning of the metal ions at the interface, a key place to initiate the oxidation reactions. A change in pH modifies the complex formation between metallic ions and proteins: hydrogen ions compete with metallic ions to bind the protein. At low pH, the anionic groups of aminoacyl residues tend to become protonated. As a consequence, their affinity for cations decreases, and therefore reduces their complexation with the protein.The presence of ferrous ion influences the oxidation rate. The ability of the complex to retain iron ion and to avoid “free” ferrous ion is very important factor to be controlled.