Infrared spectroscopic study of β-lactoglobulin interactions with flavor compounds

Fourier transform infrared spectroscopy of aqueous solutions of β-lactoglobulin is used to study the incidence of binding of small organic ligands on the protein conformation at pH 2.0 and 7.5. Differential spectroscopy allows the comparison of conformational changes for different ligands, while curve fitting techniques are used to determine the influence of ligand binding on the relative proportions of the protein's secondary structural elements. Results are presented which suggest that retinol, fatty acids and β-ionone bind to the central cavity of β-lactoglobulin. Binding of α-ionone to the same site is also likely, although clear differences exist compared to the β isomer. A number of other flavor compounds did not induce any conformational changes to the protein. It is therefore assumed that these compounds bind to the protein surface.