The folic acid/β-casein complex: Characteristics and physicochemical implications

Milk proteins are natural vehicles for bioactive molecules. Molecules of casein, the principal protein in milk, can reportedly form complexes with bioactive molecules at the molecular level. The interaction of β-casein with folic acid (a synthetic form of the B group vitamin known as folates) was studied using fluorescence, absorption spectroscopy and circular dichroism. It was found that folic acid bound to β-casein by hydrophobic contacts with a dissociation constant of ~ 10− 5 M. This interaction did not affect changes in β-casein structure caused by sodium dodecyl sulfate but did reduce the sensitivity of the structure to sodium chloride. Binding to β-casein appeared to inhibit the photodecomposition of folic acid. These results should provide insight into β-casein-bioactive-molecule interaction mechanisms and aid the development of protein-based carrier systems for the delivery of bioactive molecules.