Ethyl esters interact with the major wine Thaumatin Like Protein VVTL1

Abstract

The interactions among aromatic compounds and proteins is an important issue for the quality of foods and beverages. In wine, the loss of flavor after vinification is associated to bentonite treatment and this effect can be the result of the removal of aroma compounds which are bound wine proteins. This phenomenon was recently demonstrated for long chain fatty acids and their ethyl esters (1). Since these latter compounds are spectroscopically silent, their association with proteins is not easy to measure. Therefore, the binding of ethyl esters to a wine protein has been analyzed by studying the modifications of the protein structure (which indicates protein-ligand interactions) by Synchrotron Radiation Circular Dichroism (SRCD) spectroscopy (2). The effects induced by the addition of ethyl esters (from hexanoate to dodecanoate) on the secondary structure and stability of a purified Thaumatin like-protein (VVTL1), the most abundant wine protein, was studied in a wine model solution (12% ethanol, 5 g/l mesotartaric acid, pH 3.2). As demonstrated by UV-photo denaturation assays (20 repeated consecutive scans in the far UV-region of protein), the secondary structure of VVTL1 was only slightly affected by the presence of the selected aroma esters, but protein stability was increased by the addiction of octanoate, decanoate and dodecanoate ethyl esters. On the contrary, in the presence of ethyl hexanoate protein stability decreases. These data were further confirmed by SRCD thermal denaturation assay. The results here reported demonstrate that the content of ordered structure and the protein photo and thermal stability of the main wine protein VVTL1 is modified by ethyl esters of different chain length, indicating the existence of a binding phenomenon. Therefore esters interactions with proteins may occur in wine and that this fact can modulate both the effect of bentonite treatments and the perception of the wine aroma.

(1) Vincenzi et al., 2015. J. Agric. Food Chem., 63, 2314 (2) Hussain R. et al., 2012. Spectroscopic Analysis: Synchrotron Radiation Circular Dichroism, in: Comprehensive Chirality, 8, Elsevier, Amsterdam, pp. 438-448.

ACKNOWLEDGMENTS We thank Diamond Light Source for access to beamline B23 (SM8034) that contributed to the results presented here. This research has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement nº 226716.