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Procyanidins are widely associated with astringency perception and promptly interact/precipitate salivary proteins (SPs). In this work, the SP profile of 17 volunteers was monitored for 1 year, focusing on the SP families most related to astringency [aPRPs (acidic proline-rich proteins), bPRPs (basic proline-rich proteins), gPRPs (glycosylated proline-rich proteins), cystatins, P-B peptide, and statherin]. Although the total SP content remained constant, bPRPs showed high variability. Saliva from 5 volunteers was selected, each individual's saliva presenting a prominence in one of the referred SP families; each was used to interact with grape seed procyanidin oligomeric fraction. Independent of the prominences, a total depletion in statherin and P-B peptide was observed. These subjects performed a sensory assay and the limit of detection for astringency was determined. Overall, the specificity of SP toward procyanidins seemed to be more important in the interactions than the total SP content. The highest reactivity toward SPs was observed for epicatechin gallate, procyanidin dimers B7, B2g, and trimer C1.

At red wine pH, malvidin-3-glucoside (mv-3-glc), the major anthocyanin of red wine, is expected to be present mainly in its non-colored hemiketal form. However, due to copigmentation with flavanols (e.g. epicatechin), the stabilization of the colored forms of mv-3-glc occurs. Some flavanols have been linked to astringency, due to their ability to interact/precipitate salivary proteins, namely proline-rich proteins (PRPs). So, a major question is if this copigmentation interaction could affect the ability of flavanols to interact with SP. To answer this, the effect of the interaction between mv-3-glc and epicatechin with basic and acidic PRPs, was investigated by saturation-tranfer difference (STD)-NMR and isothermal titration calorimetry (ITC). The most relevant result was that epicatechin:mv-3-glc mixture presents a synergic effect toward the interaction with both PRPs when compared to individual polyphenols. Furthermore, was observed that epicatechin interaction was driven by hydrophobic and hydrophilic interactions while mv-3-glc interaction was driven by electrostatic interactions.

The oxidation of two premium wines, Chianti Classico and Brunello di Montalcino, obtained from Sangiovese grapes in 2017 and 2018 vintages, is simulated through oxygen exposure by applying three consecutive saturation/consumption cycles. After each oxidation cycle, wines are analyzed for color intensity, hue, CIElab coordinates, polymeric pigments, monomeric anthocyanins, acetaldehyde, tannins, and flavans and compared to control wines. By increasing the oxygen supply, monomeric anthocyanins decrease faster in the younger wines, acetaldehyde is highly produced in the older ones, while the formation of polymeric pigments depends on the wine type. The color intensity, the yellow and blue tint increase in all wines. The effect of oxidation on main phenolic compounds is more affected by the wine age than the type. Oxidation also significantly affects wine sensory characteristics: the astringency intensity decreases, whereas the subqualities of silk and velvet increase. The percentage increase of the silky sensation is from four to sevenfold higher in young wines. The silkiness is correlated with some anthocyanins decrease [malvidin 3-(6II-acetyl)-monoglucoside, delphinidin 3-monoglucoside, petunidin 3-monoglucoside, malvidin 3-monoglucoside]; the velvet sensation with polymeric pigments formation, acetaldehyde production, and malvidin 3-(6II-acetyl)-monoglucoside decrease. Moreover, after oxidation, aged wines are characterized by an enhanced balsamic odor and aroma.

Phenolic compounds (PC) are linked to astringency sensation. Astringency studies typically use simple models, with pure PC and/or proteins, far from what is likely to occur in the oral cavity. Different oral models have been developed here, comprising different oral epithelia (buccal mucosa (TR146) and tongue (HSC-3)) and other main oral constituents (human saliva and mucosal pellicle). These models, were used to study the interaction with two PC extracts, one rich in flavanols (a green tea extract) and one rich in anthocyanins (a red wine extract). It was observed that within a family of PC, the PC seem to have a similar binding to both TR146 and HSC-3 cell lines. When the oral constituents occur altogether, flavanols showed a higher interaction, driven by the salivary proteins. Conversely, anthocyanins showed a lower interaction when the oral constituents occur altogether, having a higher interaction only with oral cells. Epigallocatechin gallate, epicatechin gallate, epigallocatechin-3-O(3-O-methyl) gallate were the flavanols with the highest interaction. For the studied anthocyanins (delphinidin-3-glucoside, peonidin-3-glucoside, petunidin-3-glucoside and malvidin-3-glucoside), there was not a marked difference on their interaction ability. Overall, the results support that the different oral constituents can have a different function at different phases of food (PC) intake. These differences can be related to the perception of different astringency sub-qualities.

The impact of grape pectic polysaccharides on malvidin-3-O-β-d-glucoside thermostability was evaluated in model solutions. Pectic polysaccharides richer in homogalacturonan domains, with less neutral sidechains (chelator fraction) showed higher binding with malvidin-3-O-β-d-glucoside, by 1H NMR (Ka=505 M-1). Binding affinity with water soluble extract was estimated to be 10-fold lower, possibly due to the presence of neutral branched regions and more compacted structure, hampering the binding. Hydrophobic domains, such as rhamnogalacturonans-I domains in acid soluble polysaccharides, may participate in the formation of complexes with malvidin-3-O-β-d-glucoside. The thermostability of anthocyanin-polysaccharides complexes was evaluated at different temperatures, assessing anthocyanins degradation by HPLC-DAD. Polysaccharides showed to improve anthocyanin thermostability, with chelator and acid extract having the highest impact at lowest temperatures. Electrostatic interactions, additionally stabilized by hydrophobic effect contribute to the anthocyanin-polysaccharides binding and to the consequent thermostabilization. The protection provided by grape pectic polysaccharides foresees innovative anthocyanin food products with improved thermostability and colour features. published

In this work, high-performance liquid chromatography, fluorescence quenching, nephelometry, and sodium dodecyl sulfate polyacrylamide gel electrophoresis were used to study the effect of polysaccharides naturally present in wine [rhamnogalacturonan II (RG II) and arabinogalactan proteins (AGPs)] on the interaction between salivary proteins (SP) together present in saliva and tannins (punicalagin (PNG) and procyanidin B2). In general, the RG II fraction was more efficient to inhibit SP precipitation by tannins, especially for acidic proline-rich proteins (aPRPs) and statherin/P-B peptide, than AGPs. The RG II fraction can act mainly by a competition mechanism in which polysaccharides compete by tannin binding. However, in the presence of Na+ ions in solution, no RG II effect was observed on SP-tannin interactions. On the other hand, dependent upon the saliva sample as well as the tannin studied, AGPs can act by both mechanisms, competition and ternary (formation of a ternary complex with SP-tannin aggregates enhancing their solubility).

Polyphenols may contribute directly to plant-based foodstuffs flavor, in particular to astringency and bitterness. In this work, the bitterness of a small library of polyphenols from different classes [procyanidin dimers type B, ellagitannins (punicalagin, castalagin, and vescalagin) and phenolic acid ethyl esters (protocatechuic, ferulic, and vanillic acid ethyl esters] was studied by a cell-based assay. The bitter taste receptors (TAS2Rs) activated by these polyphenols and the half-maximum effective concentrations (EC50) of each agonist-TAS2Rs pair were determined. Computational methodologies were used to understand the polyphenol molecular region responsible for receptor activation and to get insights into the type of bonds established in the agonist-TAS2Rs pairs. The results show the combinatorial pattern of TAS2Rs activation. TAS2R5 seems to be the only receptor exhibiting a bias toward the activation by condensed tannins, while TAS2R7 seems more tuned for hydrolyzable (ellagi)tannins. Additionally, at the concentrations usually found for these compounds in foodstuffs, they can actively contribute to bitter taste, especially ellagitannins.

This work reports the study of the interaction of human salivary proteins (SP) with phenolic compounds that migrate from cork stoppers to wine. This study yields valuable data to understand the influence that these compounds may have on the sensory perception of wine from an astringency perspective. For that, three cork fractions containing the phenolic compounds that migrate in greater amounts from cork to model wine solutions were selected. Fraction M1 contains gallic acid, protocatechuic acid, vanillin and protocatechuic aldehyde; fraction M2 comprises essentially gallic acid and ellagic acid, as well as castalagin and dehydrocastalagin; and fraction M3 contains the two isomeric ellagitannins castalagin and vescalagin. The reactivity of each fraction towards SP was M3 > M2 > M1. Within M3 fraction, castalagin showed a higher ability to precipitate SP (mainly aPRPs, statherin and P-B peptide) comparatively to vescalagin. In M1 fraction, caffeic and sinapic acids were the compounds with the highest interaction with SP, mainly cystatins. In addition, there also seems to be a matrix effect (presence of other compounds) that could be affecting these interactions.

In this study, water and chelator-soluble pectic polysaccharide fractions were obtained from white grape skins, aiming to study their impact on the interaction between low polymerized grape seed procyanidins and salivary proteins. Water and chelator-soluble polysaccharide fractions were composed by uronic acids and neutral sugars, mainly arabinose and galactose, with water polysaccharide fraction showing a higher amount of branched pectic polysaccharides. Both polysaccharide fractions were able to mitigate salivary protein-procyanidin interactions, by a competition mechanism, resulting in a decrease of the amount of precipitated protein. Water polysaccharide fraction was the most effective in inhibiting salivary protein precipitation, especially for acidic proline-rich proteins, due to the higher affinity to interact with procyanidins (KA = 22222 M-1 and KA = 365 M-1 for water and chelator polysaccharides, respectively). The interaction between polysaccharides and procyanidins showed to be mainly governed by hydrophobic effect.

The first contact of tannins with the human body occurs in the mouth, where some of these tannins are known to interact with salivary proteins, in particular with proline-rich proteins (PRPs). These interactions are important at a sensory level, especially for astringency development, but could also affect the biological activities of the tannins. This study gathers information on the relative affinity of the interaction, complex stoichiometry, and tannin molecular epitopes of binding for the interactions between the families of PRPs (bPRPs, gPRPs, and aPRPs) and three representative ellagitannins (castalagin, vescalagin, and punicalagin). These interactions were studied by saturation-tranfer difference NMR and microcalorimetry. The effect of the PRP-ellagitannin interaction on their antioxidant ability was also assessed by ferric reduction antioxidant power (FRAP) assays. The results support a significant interaction between the studied tannins and PRPs with binding affinities in the micromolar range. Punicalagin was always the ellagitannin with higher affinity. aPRPs were the salivary PRPs with higher affinity. Moreover, it was observed that when ellagitannins are present in low concentrations (5-50 μM), as occurs in food, the antioxidant ability of these tannins when complexed with salivary PRPs could be significantly impaired.

International audience; Throughout the apple juice and cider making process, polyphenols undergo enzymatic oxidation which generates a great variety of polyphenol oxidation products. Since 5 '-O-Caffeoylquinic acid (CQA) is one of the major phenolic compounds and the preferential substrate for polyphenoloxidase in apple juice, its oxidation leads to the formation of newly formed molecules by which dehydrodimers (MW 706 Da) are included. Interactions of salivary proteins (SP) with native polyphenols is a well-known phenomenon, but their interactions with poly phenol oxidation products has not been studied yet. In this work, we decided to decipher the interactions between CQA dehydrodimers and SP (gPRPs, aPRPs, statherins/P-B peptide, and cystatins) using HPLC-UV and fluorescence. These results showed that contrary to what was expected, CQA dehydrodimers presented a low interaction with PRPs, but revealed a specific interaction with statherins/P-B peptide and cystatins. This work settles for the first time the interactions between SP and polyphenol oxidation products.

The most widely accepted mechanism to explain astringency is the interaction and precipitation of salivary proteins by food tannins, in particular proline-rich proteins. However, other mechanisms have been arising to explain astringency, such as binding of tannins to oral cells. In this work, an experimental method was adapted to study the possible contribution of both salivary proteins and oral cells to astringency induced by grape seed procyanidin fractions. Overall, in the absence of salivary proteins, the extent of procyanidin complexation with oral cells increased with increasing procyanidin degree of polymerization (mDP). Procyanidin fractions rich in monomers were the ones with the lowest ability to bind to oral cells. In the presence of salivary proteins and for procyanidins with mDP 2 the highest concentrations (1.5 and 2.0 mM) resulted in an increased binding of procyanidins to oral cells. This was even more evident for fractions III and IV at 1.0 mM and upper concentrations. Regarding the salivary proteins affected, it was possible to observe a decrease of P-B peptide and aPRP proteins for fractions II and III. This decrease is greater as the procyanidins' mDP increases. In fact, for fraction IV an almost total depletion of all salivary proteins was observed. This decrease is due to the formation of insoluble salivary protein/procyanidin complexes. Altogether, these data suggest that some procyanidins are able to bind to oral cells and that the salivary proteins interact with procyanidins forming salivary protein/procyanidin complexes that are also able to link to oral cells. The procyanidins that remain unbound to oral cells are able to bind to salivary proteins forming a large network of salivary protein/procyanidin complexes. Overall, the results presented herein provide one more step to understand food oral astringency onset.

Polyphenols interaction with salivary proteins (SP) has been related with organoleptic features such as astringency. The aim of this work was to study the interaction between some human SP and tannins through two spectroscopic techniques, fluorescence quenching, and saturation transfer difference-nuclear magnetic resonance (STD-NMR). Generally, the results showed a significant interaction between SP and both condensed tannins and ellagitannins. Herein, STD-NMR proved to be a useful tool to map tannins’ epitopes of binding, while fluorescence quenching allowed one to discriminate binding affinities. Ellagitannins showed the greatest binding constants values (KSV from 20.1 to 94.1 mM–1; KA from 0.7 to 8.3 mM–1) in comparison with procyanidins (KSV from 5.4 to 40.0 mM–1; KA from 1.1 to 2.7 mM–1). In fact, punicalagin was the tannin that demonstrated the highest affinity for all three SP. Regarding SP, P-B peptide was the one with higher affinity for ellagitannins. On the other hand, cystatins showed in gener...

In this work, saturation transfer difference-NMR, isothermal microcalorimetry and molecular dynamics simulations have been used to study the individual interactions between basic, glycosylated and acidic proline-rich proteins (bPRPS, gPRPs, aPRPs) and P-B peptide with some representative food tannins [procyanidin B2, procyanidin B2 3'-O-gallate (B2g) and procyanidin trimer (catechin-4-8-catechin-4-8-catechin)]. Results showed that P-B peptide was in general the salivary protein (SP) with higher affinity whereas aPRPs showed lower affinity to the studied procyanidins. Moreover, B2g was the procyanidin with higher affinity for all SP. Hydrophobic and hydrogen bonds were present in all interactions but the major driving force depended on the procyanidin-SP pair. Furthermore, proline clusters or residues in their vicinity were identified as the probable sites of proteins for interaction with procyanidins. For bPRP and aPRP a significant change to less extended conformations was observed, while P-B peptide did not display any structural rearrangement upon procyanidins binding.

Astringency is closely related to the interaction between procyanidins and salivary proteins (SP). The aim of this work was to study the interaction between mucin, a SP responsible for saliva lubricating properties, with different procyanidins (B4 dimer, tetramer (TT) and fractions of oligomeric procyanidins), and the influence of several conditions [pH, ionic strength, procyanidins' mean degree of polymerization (mDP) and different solvents (ethanol or dimethylsulfoxide)] on this interaction by fluorescence quenching and Saturation Transfer Difference (STD)-NMR. For fractions of oligomeric procyanidins, the mucin-procyanidin interaction increased with mDP; however, for pure compounds, procyanidin TT has lower affinity than dimer B4 which could be due to a lower structural flexibility imposed by its complex structure. Furthermore, EtOH and DMSO can disrupt the main driving forces of these interactions, hydrophobic interactions and hydrogen bonds, respectively, lowering significantly the binding constants.