Interactions between aroma compounds and β-lactoglobulin in the heat-induced molten globule state

The present study aims to elucidate the binding of small hydrophobic ligands onto the molten globule state of β-lactoglobulin (BLG). The conversion of the native BLG into a molten globule state was induced by heat treatment at acidic pH. The molten globule state was evidenced by far and near-UV circular dichroism spectra. β-Ionone and guaiacol exhibited a higher binding ability to BLG in the heat-induced molten globule state compared to unheated BLG, as assessed by protein surface hydrophobicity measurements, using 6-propionyl-2-(dimethylamino)naphthalene (PRODAN) fluorescent probe. The binding sites of the two aroma compounds were determined by 2D nuclear magnetic resonance (NMR) spectroscopy. The less tightly packed structure of the molten globule favoured ligand binding, in particular within the central cavity. The greater flexibility of the calyx entrance, and the conformational change of loop EF induced an easier access of the central cavity after the thermal treatment.