Interactions of α-ionone, β-ionone and vanillin with the primary genetic variants of β-lactoglobulin

Abstract Interactions between bovine β-lactoglobulin (β-Lg) genetic variants (A, B and a mixture thereof) and α-ionone, β-ionone and vanillin were studied by tryptophan fluorescence spectroscopy under various conditions of pH and ionic strength. When β-ionone was added to β-Lg, we found progressive increase in quenching from pH 3.0 to pH 8.0 and relative decrease at pH 11.0. Fluorescence quenching progressively increased from pH 3.0 through to pH 11.0 when vanillin was added. Small differences in quenching of variants β-Lg variants A and B were observed at pH 8.0 for β-ionone, but not for vanillin at any pH. NaCl affected the fluorescence quenching of β-Lg by β-ionone at pH 7.0 and 8.0 and by vanillin at pH 8.0 and 11.0. No apparent interaction between α-ionone and β-Lg was observed under the conditions studied. The results suggest that β-ionone and vanillin bind at different domains of β-Lg, possibly with different binding mechanisms.