A Combined Spectroscopy and Computational Molecular Docking Investigation on the Coupling Between β-lactoglobulin Dimers and Vanillin

Protein - flavor interactions may influence flavor perception in food products and, therefore, they need to be deeply under-stood, at the molecular scale. We investigated the coupling between the bovine whey protein beta-lactoglobulin (beta-lg) and the vanillin (VAN), the main compound present in the flavor vanilla, at pH 7.1 (which is representative of close-to-neutral food formulations). Fluorescence quenching data showed that the static quenching mechanism was predominant in the beta-lg/vanillin complexes formation, and allowed estimating its thermodynamic parameters delta HVAN/p-lg = -30.3kJ . mol(-1), delta SVAN/fl-lg = -45.8J . mol(-1)K(-1), and delta G(VAN/p-lg) ranging from -16.9 to -16.5kJ . mol(-1), showing that the beta-lg-VAN com-plexation was spontaneous and enthalpically driven, with the involvement of both hydrogen bonding and hydrophobic interactions. In silico molecular docking assays were undertaken to identify the specific binding sites and to verify the nature of intermolecular interactions between beta-lg and VAN. At pH 7.1, beta-lg forms dimers in aqueous medium, and this important fact was considered. Molecular docking results showed that vanillin may bind to two possible sites: A-site (interface between the two beta-lg monomers) and B-site (beta-barrel entrance of beta-lg). The conjoint analysis of in vitro and in silico findings indicated that the B-site is more likely to be the binding site of beta-lg for the vanillin mol-ecule. Indeed, while in the A-site hydrogen bonds seemed to be stronger, in the B-site there was a balance between the presence of hydrogen bonds, electrostatic interactions, and hydrophobic interactions, in particular involving aromatic amino acid residues. The beta-lg amino acid residues involved in these interactions were Trp19, Tyr20, Val43, Glu44, Leu156, Glu157, and His161.

Automated summary

This study investigated the interaction between bovine whey protein beta-lactoglobulin (beta-lg) and vanillin, the main compound in vanilla flavor. Experimental results showed that the formation of beta-lg/vanillin complexes was driven by both hydrogen bonding and hydrophobic interactions. Molecular docking simulations revealed that vanillin could bind to two possible sites, with the B-site being the more likely binding site.