Effect of iron chelates on oil-water interface, stabilized by milk proteins: The role of phosphate groups and pH. Prediction of iron transfer from aqueous phase toward fat globule surface by changes of interfacial properties

Iron incorporated into food systems induces oxidation and precipitation. The consequences are reduced bioavailability and a functional modification of other food components such as proteins. The iron-chelates such as ferrous bisglycinate represent a possibility to avoid side effects, since the iron is protected. The aim of this study is to investigate the effects of iron-chelates compounds on the properties of an oil/water interface stabilized by caseinate or beta-lacotoglobulin, under environmental conditions at 20 degrees C. Analyses were performed using dynamic drop tensiometry during 5000 s. The aqueous bulk phase is an imidazole/acetate buffer (0.1 M), containing 0.4 x 10(-6) M protein, and 0.2 x 10(-6) 9 M iron-chelates compounds. The results indicate that, under neutral conditions, the addition of some irons salts (NaFeEDTA or Fe-bisglycinate) do not change the structure of the interface stabilized by a protein containing no phosphate groups (beta-lactoglobulin). In the case of caseinate, NaFe-EDTA addition increases the lowering rate of surface tension at pH 6.5. On the contrary, the lowering rate of surface tension with caseinate is inhibited by Fe-bisglycinate at pH 6.5. Such an effect is not observed with beta-lactoglobulin. The low transfer of irons ions from the bulk to the interface stabilized by beta-lactoglobulin is confirmed by zeta-meter and FTIR measurements. These results indicate an effective strategy to follow for controlling the physical and chemical stability of an emulsion stabilized with proteins. (C) 2009 Elsevier Ltd. All rights reserved.