Study of the interactions between wine anthocyanins and proline rich proteins

Abstract

The interaction between tannins and salivary proteins is considered to be the basis of the phenomenon of wine astringency. Recently, some authors have revealed that some anthocyanins can also contribute to this mouthfeel sensation by interacting with proline rich proteins (PRPs). However, more studies are needed in order to elucidate the affinity of anthocyanins with these proteins.

Thus, the general objective of this work was determine the interaction between malvidin-3-O-glucoside, malvidin-3-O-(6-O-acetyl)-glucoside, and malvidin-3-O-(6-O-p-coumaroyl)-glucoside (isolated from grape skin) with a PRP model peptide (IB7-14) and their capacity of precipitate PRPs in a wine model solution. To archived this objectif, several techniques were used: i) mass spectrometry (FIA-ESI-QTOF) and 1H proton NMR to determine the formation of complexes and the stoichiometry of anthocyanins-IB7-14 complexe ii) saturation transfer difference (STD) NMR spectroscopy in order to calculate the dissociation constants (KD) and the affinity of each anthocyanin with the peptide and, iii) HPLC-DAD that was used to evaluate the capacity of anthocyanins to precipitate PRPs (isolated from human saliva).

Our results demonstrate that anthocyanins are able to interact with IB7-14, with different stoichiometries and binding strengths. A stoichiometry of 3:1 for the malvidin-3-O-glucoside-peptide, 1:1 for the acetylated form, and 4:1 for the coumaroylated form were observed. These ratios was also confirmed by 1H proton NMR. According to the obtained dissociation constants, the affinity of malvidin-3-O-glucoside (17.5 mM) was much higher than for malvidin-3-O-(6-O-acetyl)-glucoside (order of hundred mM). Unfortunately, the calculation of KD for malvidin-3-O-(6-O-p-coumaroyl)-glucoside was impossible due to precipitate formation. To finish, when malvidin-3-O-(6-O-p-coumaroyl)-glucoside was mixed with human salivary PRPs we observed that the precipitation of PRPs was much higher (14%) than for malvidin-3-O-glucoside (7%). In the same way, malvidin-3-O-(6-O-acetyl)-glucoside did not lead a significant decrease of their quantities when it was in contact with PRPs, suggesting the absence of interactions. It could be hypothesized that the additional presence of an aromatic group of coumaroylated form of malvidin could provide stronger hydrophobic bonds than malvidin-3-O-glucoside. Likewise, the chemical structural differences between malvidin-3-O-glucoside and malvidin-3-O-(6-O-acetyl)-glucoside can cause a potential loss of hydrogen bonding preventing thus the stabilization between the anthocyanin and the peptide. These findings proved for the first time that wine anthocyanins interact differently with the peptide IB7-14 and that can potentially affect the astringency sensation.

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