Oxidative stability of oil-in-water emulsions containing iron chelates: Transfer of iron from chelates to milk proteins at interface

Iron supplementation can promote oxidation of food matrices as well as cell lipids. The oxidative stability of oil/water emulsions stabilised by β-lactoglobulin (BLG) or sodium caseinate (SC) was studied in the presence of Fe-bisglycinate, NaFe-EDTA or FeSO4. Lipid oxidation was evaluated by following the peroxide value (PV) and the thiobarbituric acid reactive substances (TBARS) over 7 days. At pH 6.5, for Fe-bisglycinate iron complement, the oxidation kinetics was more reduced with BLG than with SC. Contrarily to BLG, SC possesses phosphate groups that have more affinity for iron ions than carboxylate residues. Both BLG and SC stabilised emulsions were more oxidised with Fe-bisglycinate or FeSO4 than with NaFe-EDTA. At pH 3.5, lipid oxidation was higher compared to pH 6.5. These results indicate that the competition for iron complexation between functional groups of protein and salt counter-ions (glycinate, sulphate or EDTA) appear as a key factor in oxidation.