Interactions between different forms of bovine lactoferrin and sodium alginate affect the properties of their mixtures

Abstract

The interactions between different forms (apo-, native- and holo-) of lactoferrin (Lf) and sodium alginate at different ratios in aqueous solution in the pH range of 4–7 were evaluated. Fourier transform infra-red (FTIR) spectra of freeze dried mixtures showed shifts only in the bands arising from the carboxylate groups of alginate relative to physical mixtures; indicating intermolecular interactions involving COOˉ moieties of alginate. Circular dichroism (CD) spectroscopy showed that Lf retained its tertiary structure in the Lf-alginate mixtures. In the pH range of 4–7, the zeta-potential of Lf-alginate solutions was significantly less negative than that of alginate indicating charge compensation. Native-PAGE results indicated that the extent of binding of Lf by alginate was dependent of the form of Lf with apo-Lf displaying a higher binding affinity. At natural pH, the Lf-alginate mixtures generated higher viscosities than their respective sodium alginate controls indicating the existence of intermolecular interactions between the two components. A mixture of native-Lf and sodium alginate showed the highest increase in the viscosity while increasing level of iron saturation in Lf showed an inverse effect on viscosity. DSC analysis showed that the thermal denaturation temperature of native- and holo-Lf can be enhanced upon interaction with alginate in solution.