Binding studies and computer-aided modelling of macromolecule/odorant interactions.

Odorant-to-biopolymer (proteins and polysaccharides) binding properties influence the partition coefficients of odorant/matrix mixtures and depend on the molecular structure of the guest and the host. While air/solvent partition coefficients of odorants influence the flavor intensity of compounds in the headspace above the solvent, more complex mechanisms are proposed for the binding of a molecule to a food matrix. Odorant air/solvent partition coefficients are dependent on both the physico-chemical properties of odorant and solvent. Binding affinities for flavor compounds on various biopolymers can be estimated by calculation of physico-chemical descriptors for the odorants. Binding affinities of gamma- and delta-lactones (C7-C11) to bovine serum albumin (BSA) and beta-lactoglobulin (BLG) were investigated by ultracentrifugation and equilibrium-dialysis techniques. Quantitative structure-activity relationships (QSAR) of lactone binding on proteins (BLG and BSA) were performed by the measurement of lipophilicity and H-bond strength. Large differences in observed protein-binding properties for the various compounds clearly demonstrated that structure-activity relationship was significantly influenced by the lipophilicity of the odorant. If the structure of the receptor molecule is known, computational ligand-macromolecule docking experiments can be used to predict binding affinities for unknown compounds with the receptor molecule. A BLG-lactone binding position, not previously reported in the literature, has been identified and confirmed by competitive binding studies. A model has been developed to estimate the free energy of binding of odorants to biopolymers. Estimated free energies of binding of lactones with BLG from computational methods were in very good agreement with the experimentally obtained results.