Binding analysis between monomeric β-casein and hydrophobic bioactive compounds investigated by surface plasmon resonance and fluorescence spectroscopy

beta-Casein, a phosphoprotein representing 37% of the bovine milk caseins, has specific features promoting its application as a nanocarrier for hydrophobic bioactives. In this study, the interactions of beta-casein with curcumin and vitamin D3 under the same physico-chemical conditions were investigated. The interaction kinetics have been studied by surface plasmon resonance (SPR) and fluorescence spectroscopy. The KD value for curcumin-beta-casein interaction has been successfully evaluated (4.1 +/- 0.7 x 10(-4) M) using SPR by fitting data to a 1:1 Langmuir interaction model. Conversely, the SPR responses obtained for vitamin D3 show that the interactions between this hydrophobic compound and the beta-casein immobilized on the sensor chip were below the sensitivity of the SPR apparatus. Moreover, the fluorescence quenching data show that curcumin has higher affinity to beta-casein (K-A = 23.5 +/- 1.9 x 10(4) M-1) than vitamin D3 (K-A = 5.8 +/- 1.1 x 10(4) M-1).