Binding of odorants to individual proteins and their mixtures. Effects of protein denaturation and association. A plasticized globule state

The unfolding-association-refolding behaviour of proteins and their interactions with odorants are significant to the processing and flavoring of foods. Interactions of 2-octanone and vanillin (aliphatic and aromatic odorants) with individual proteins and their mixtures have been studied using: native, acid and thermally denatured bovine serum albumin (BSA), native and thermally denatured ovalbumin (OA) and bovine β-casein (BC). Equilibrium dialysis and differential scanning calorimetry methods were used to study flavor binding and flavor release in protein solutions. The binding of vanillin to native BSA exhibited two equivalent binding sites with binding constants in the order of 103 M−1 and these binding parameters were not markedly changed within the range of temperature from 25 to 63 °C. The binding site number was monotonously reduced to about zero as the pH was decreased from 6.4 to 2.5, consistent with the N⇔F transition of BSA. The complete loss of vanillin binding activity was also coupled with both acid and thermal denaturation of BSA. Neither the associated BC nor thermally denatured OA produced a detectable competition with BSA for the binding of vanillin or octanone. The associated BC did not bind vanillin. It has been proposed that the adsorption of hydrophobic low-molecular weight compounds acts to plasticize the globule state of the protein. Plasticized globular proteins seem to tend towards self-association and refolding with separation of hydrophobic ligands (e.g. odorants).