β-Carotene and milk protein complexation: a thermodynamic approach and a photo stabilization study

Abstract

The demand for bioactive molecules, such as β-carotene (β-car), has increased, but some characteristics such as low water solubility and low photo stability limit its application in many formulations. The bioactive entrapment into milk proteins may overcome this barrier. Thus, the aim of this work was to study the interaction between β-car and bovine serum albumin (BSA) or β-casein and the photo stability of this bioactive in the presence of the proteins. Fluorescence spectroscopy showed that at pH 7.0, increasing concentrations of β-carotene reduced the fluorescence intensity of both proteins, and the fluorescence-quenching mechanism is mainly static. The stoichiometry of the β-car/protein complex varied between proteins, being 1:1 to native BSA, 1:3 to denatured BSA (d-BSA), and 1:2 for β-casein. The standard Gibbs-free energy (ΔG°) of complex formation was negative for all systems studied and followed the order ΔG°BSA < ΔG°β-casein < ΔG°d-BSA. The formation of β-car/protein complex was driven by entropy increasing in all studied conditions. Both proteins improved β-car photo stability, but β-casein micelle was more efficient, reducing and increasing four times, respectively, the bioactive degradation constant and the half-time of β-car. The overall results pointed to the strategic use of milk proteins, especially β-casein micelles as nanovehicle for β-car in food and other systems.