Effect of thermal denaturation on vanillin binding to some food proteins

Interactions of food proteins--beta-lactoglobulin (BLG), bovine serum albumin (BSA) und ovalbumin (OA)--with vanillin and effect of thermal denaturation of the proteins on vanillin binding were studies by US-VIS spectrophotometry. This method has its origin in characteristic changes in the vanillin absorption spectrum at vanillin-protein complex formation and allows to calculate concentrations of the bound and free ligand in aqueous solutions. Thermodynamic parameters, the intrinsic association constants and the number of binding sites of the vanillin binding to the native and thermodenaturated proteins (monomers and clusters) were determined. It is shown that the vanillin affinity for the native proteins is decreased in the following order: BSA > BLG > OA. This sequence is reversed for the protein thermoclusters. The stepwise annealing allowing to derive complex protein mixtures composed of different types of the native and denatured protein mixtures composed of different types of the native and denatured protein particles was applied to thermodenaturation of BSA. The vanillin affinity for BSA is decreased in the order: native protein > denaturated monomer > denaturated clusters. Vanillin interaction with the proteins is mainly electrostatic in nature.