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Lignosulfonate (LS), kraft lignin (KL), and organosolv lignin (OL) were evaluated as potential modulating agents of the physicochemical properties of Port wine at two different concentrations for 7 and 30 days. KL and LS demonstrated the ability to remove proteins and potentiate the anthocyanin concentration. LS reduced the tannin content and the interaction of salivary acidic proline-rich proteins with wine phenolic compounds. None of the lignin promoted a perceptible color change; however, the yellowish color of KL and OL at 100 g/hL contributed to an increase in the yellow tones of wines. Lignin improved wine aroma by reducing the amount of unwanted volatiles by 30% and increasing the content of ethyl esters associated with fruity aromas by up to 60%. The results suggest that lignin, especially LS, can be employed as a modulating agent, positively impacting wine's physicochemical properties. This valorization of a byproduct opens up new opportunities for the wine industry.

Some germination is known to occur during the process of fermentation in cocoa beans. The impact of this biological process on the course of cocoa fermentation is not known and was thus investigated. In order to determine the impact of germination at the molecular level as well as on flavor, an untargeted metabolomics approach using Ultra Performance Liquid Chromatography-Electrospray Ionization-Time of Flight-Mass Spectrometry (UPLC-ESI-ToF-MS) with simultaneous acquisition of low- and high-collision energy mass spectra (MS e ) was performed. Extracts of raw and germinated cocoa beans of the same origin were measured and compared for characteristic differences by unsupervised principal component analysis. OPLS-DA revealed 12-hydroxyjasmonic acid (HOJA) sulfate, (+)-catechin and (-)-epicatechin as most down-regulated compounds as well as two hydroxymethylglutaryl (HMG) glucosides A and B among others as decisive up-regulated compounds in the germinated material. Additionally, further HMG glucosides and 12-hydroxyjasmonic acid could be identified in cocoa for the first time by coelution with isolated and synthesized reference compounds. HOJA sulfate, which has been postulated in cocoa, and HOJA were revealed to impart bitter and astringent taste qualities.

Beyond the key bitter compound kaempferol 3- O -(2‴- O -sinapoyl-β-d-sophoroside) previously described in the literature ( 1 ), eight further bitter and astringent-tasting kaempferol glucosides ( 2 - 9 ) have been identified in rapeseed protein isolates ( Brassica napus L.). The bitterness and astringency of these taste-active substances have been described with taste threshold concentrations ranging from 3.3 to 531.7 and 0.3 to 66.4 μmol/L, respectively, as determined by human sensory experiments. In this study, the impact of 1 and kaempferol 3- O -β-d-glucopyranoside ( 8 ) on TAS2R-linked proton secretion by HGT-1 cells was analyzed by quantification of the intracellular proton index. mRNA levels of bitter receptors TAS2R3, 4, 5, 13, 30, 31, 39, 40, 43, 45, 46, 50 and TAS2R8 were increased after treatment with compounds 1 and 8 . Using quantitative UHPLC-MS/MS MRM measurements, the concentrations of 1 - 9 were determined in rapeseed/canola seeds and their corresponding protein isolates. Depending on the sample material, compounds 1 , 3 , and 5 - 9 exceeded dose over threshold (DoT) factors above one for both bitterness and astringency in selected protein isolates. In addition, an increase in the key bitter compound 1 during industrial protein production (apart from enrichment) was observed, allowing the identification of the potential precursor of 1 to be kaempferol 3- O -(2‴- O -sinapoyl-β-d-sophoroside)-7- O -β-d-glucopyranoside ( 3 ). These results may contribute to the production of less bitter and astringent rapeseed protein isolates through the optimization of breeding and postharvest downstream processing.

In this work, three MP extracts obtained from Torulaspora delbrueckii were added to red wine, and the changes in phenolic composition, color, and astringency were evaluated by HPLC-DAD-ESI-MS, tristimulus colorimetry, and sensory analysis, respectively. The MP extracts modified wine phenolic composition differently depending on the type of MP. Moreover, two MP extracts were able to reduce wine astringency. The fact that the MP-treated wines showed an increased flavanol content suggests the formation of MP-flavanol aggregates that remain in solution. Furthermore, the formation of these aggregates may hinder the interaction of flavanols with salivary proteins in the mouth. The effect of these MPs might be associated with their larger size, which could influence their ability to bind flavanols and salivary proteins. However, one of the astringent-modulating MPs also produced a loss of color, highlighting the importance of assessing the overall impact of MPs on the organoleptic properties of wine.

It is well known that repeated exposure to phenolic compounds (PCs) raises astringency perception. However, the link between this increase and the oral cavity's interactions with salivary proteins (SPs) and other oral constituents is unknown. To delve deeper into this connection, a flavonoid-rich green tea extract was tested in a series of exposures to two oral cell-based models using a tongue cell line (HSC3) and a buccal mucosa cell line (TR146). Serial exposures show cumulative PC binding to all oral models at all concentrations of the green tea extract; however, the contribution for the first and second exposures varies. The tongue mucosal pellicle (HSC3-Mu-SP) may contribute more to first-stage astringency (retaining 0.15 ± 0.01 mg mL -1 PCs at the first exposure), whereas the buccal mucosal pellicle (TR146-Mu-SP) retained significantly less (0.08 ± 0.02 mg mL -1 ). Additionally, increased salivary volume (SV+), which simulates the stimulation of salivary flow brought by a food stimulus, significantly enhances PC binding, particularly for TR146 cells: TR46-Mu-SP_SV+ bound significantly higher total PC concentration (0.17 ± 0.02 mg mL -1 ) than the model without increased salivary volume TR146-Mu-SP_SV- (0.09 ± 0.03 mg mL -1 ). This could be associated with a higher contribution of these oral cells for astringency perception during repeated exposures. Furthermore, PCs adsorbed in the first exposure to cell monolayer models (+TR146 and +HSC3) change the profile of PCs bound to these models in the second exposure. Regarding the structure binding activity, PCs with a total higher number of hydroxyl groups were more bound by the models containing SP. Regarding the SP, basic proline-rich proteins (bPRPs) may be involved in the increased perception of astringency upon repeated exposures. The extent of bPRP precipitation by PCs in mucosal pellicle models for both cell lines (HSC3 and TR146) in the second exposure (76 ± 13 and 83 ± 6%, respectively) was significantly higher than in the first one (25 ± 14 and 5 ± 6%, respectively).

Astringency is a highly complex sensation which involves multiple mechanisms occurring simultaneously, such as the interaction between flavan-3-ols and salivary proteins (SP). Moreover, astringency development can be affected by the presence of polysaccharides such as mannoproteins (MP). The aim of this work was to evaluate the molecular mechanisms whereby MP could modulate the astringency elicited by tannins, using a cell-based model of the oral epithelium (TR146 cells), and the effect of salivary proteins on these interactions. The binding of flavan-3-ols to oral cells was evaluated by DMACA assay, while the content of unbound flavan-3-ols after the interactions was assessed by means of HPLC-DAD-MS. Results obtained confirm the existence of cell-tannin interactions, that can be partially inhibited by the presence of SP and/or MP. The most significant decrease was obtained in the system containing MPF (38.16%). Both mannoproteins assayed seem to have modulating effect on flavan-3-ol-SP interactions, acting by two different mechanisms: MPF would lead to the formation of SP/MPF/flavan-3-ols ternary soluble aggregates, while MPL seems to prevent flavan-3-ol-saliva interaction by a competitive mechanism, i.e., MPL would reduce cell-tannin interactions, similar to SP. This study suggests that mannoproteins with different compositional characteristics could exhibit preferential interaction with distinct flavan-3-ol families.

Historically often described as the food of gods, cocoa-based products exhibit a pleasant aroma as well as a desirable astringent, bitter, and sour taste, which results in a high consumer preference. The key taste components of cocoa were identified and characterized by combining sensory analysis, fractionation, and structure elucidation. Cocoa astringency is driven by N -phenylpropenoyl-l-amino acids, polyphenol glycosides, and flavan-3-ols, while the latter compound class also contributes to bitterness. The key principle for cocoa bitterness was shown to be the combination of alkaloids and 2,5-diketopiperazines. To understand the influence of plant genetics, breeding, and processing on the sensory profile of cocoa products, high-throughput sensometabolite quantitation must be performed throughout all of these steps. In this work, we present a rapid, sensitive, and robust quantitation method on a single ultra-high-performance liquid chromatography tandem mass spectrometry (UHPLC-MS/MS) platform, requiring minimal workup for any sample type from farm to fork. This method was applied to a global set of 75 cocoa bean samples from all over the world before and after using a uniform roasting protocol. Within this world map, geographical origin did not predetermine cocoa taste profiles, whereas simulated processing by roasting was confirmed to be crucial in profile development. This method will open avenues for further studies to ultimately enable chocolate producers to control and optimize the taste properties of products as well as to monitor raw material selection and processing.

Flavor is one of the main drivers of food consumption and acceptability. It is associated with pleasure feels during eating. Flavor is a multimodal perception corresponding to the functional integration of information from the chemical senses: olfaction, gustation, and nasal and oral somatosensory inputs. As a result, astringency, as a sensation mediated by the trigeminal nerves, influences food flavor. Despite the importance of astringency in food consumer acceptance, the exact chemosensory mechanism of its detection and the nature of the receptors activated remain unknown. Herein, after reviewing the current hypotheses on the molecular origin of astringency, we proposed a ground-breaking hypothesis on the molecular mechanisms underpinning this sensation as a perspective for future research.

Wine is very often consumed with a meal. However, although it is well known to tasters that the taste of wine changes in the presence of food, the influence of dietary lipids on wine astringency and bitterness caused by grape tannins is not well established from a molecular point of view. In this context, we investigated wine tannin-lipid interactions by combining biophysical techniques to sensory analysis. Nuclear magnetic resonance and optical and electron microscopy showed an interaction between catechin, a majority component of grape tannins, and lipid droplets from a phospholipid-stabilized oil-in-water emulsion, characterized by (a) an increase in the droplet size in the presence of catechin, (b) slowing of their size growth over time, and (c) an increase in lipid dynamics in the droplet interfacial layer. Those results were strengthened by sensory analysis, which demonstrated that dietary oils decrease the perception of astringency of grape tannin solutions. Our results highlight that dietary lipids are crucial molecular agents impacting our sensory perception during wine consumption.

It is known that interactions between wine flavanols and salivary proline-rich proteins (PRPs) are one of the main factors responsible for wine astringency. The addition of commercial yeast mannoproteins (MPs) to wines has been pointed to as a possible tool to modulate the excessive astringency due to a lack of phenolic maturity at harvest time that might occur as a consequence of global climate change. The aim of this work was to study by isothermal titration calorimetry and molecular dynamics simulation the molecular mechanisms by which mannoproteins could modulate astringency elicited by tannins and if it can be influenced by mannoprotein composition. Results obtained indicate that the MPs assayed had an important impact on astringency through the formation of ternary aggregates with different solubilities or by preventing the flavanol-PRP interaction by a competitive mechanism, although in a different strength, depending on the size and the compositional characteristic of the mannoprotein.

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.

One of the most accepted mechanisms of astringency consists of the interaction between polyphenols and some specific salivary proteins. This work aims to obtain further insights into the mechanisms leading to a modulation of astringency elicited by polyphenols. The effect of the presence of different chemical species (present in food and beverages as food additives) on the polyphenol-protein interaction has been evaluated by means of techniques such as sodium dodecyl sulfate polyacrylamide gel electrophoresis and cell cultures using a cell-based model of the oral epithelium. Results obtained showed that several chemicals, particularly sodium carbonate, seem to inhibit polyphenol binding to salivary proteins and to oral epithelium. These results point out that polyphenol-saliva protein interactions can be affected by some food additives, which can help to better understand changes in astringency perception.

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).

The responsibility of condensed tannins in the astringency sensation is well-known, even though the physical mechanism is unclear. The aims of the study are to go deeper into the relationships between the tannin structure and red wine dryness as well as evaluate the influence of the wine matrix and tannin concentration on the interaction with proteins and dryness perception. Condensed tannins were extracted from two red wines (cv. Cabernet Sauvignon and Pinot Noir) and added back to them and to a model wine at 0.5 g/L, prior to chemical characterization of their composition by reversed-phase high-performance liquid chromatography as well as their viscosity. The physical consequences of interactions between mucin, poly-l-proline, saliva, and wines were evaluated by turbidimetry. Descriptive analysis and time-intensity evaluations of dryness were carried out by a trained panel on all wines and model solutions. The mean degree of polymerization of Cabernet Sauvignon wine with or without tannins added was higher than that of Pinot Noir wine conditions. The turbidity of saliva and poly-l-proline with tannins added to Cabernet Sauvignon was higher than of tannins added to Pinot Noir wine. Cabernet Sauvignon wines were perceived dryer than Pinot Noir by panelists, and the dryness intensity of Cabernet Sauvignon wine conditions last longer than that of Pinot Noir or model wine conditions. The dryness of red wines was related to larger tannins, higher tannin concentration, and a greater turbidity with saliva. The dryness was not affected by the addition of tannins into wine probably as a result of the aroma/taste suppression effects and the presence of other components.

Some polyphenols have unpleasant taste properties such as astringency, which could interfere with consumers' choices. The knowledge on astringency mechanisms points that astringency is a complex phenomenon probably related to more than one physical-chemical mechanism. Thus, this work aims to develop a new and more realistic cell-based model containing human saliva, mucosa pellicle, and an oral cell line (HSC-3) to understand the oral molecular events that could contribute to the overall astringency perception. This model was then used to study the interactions with a food procyanidin fraction (PF) by HPLC. In general, the results revealed higher interaction (synergism) for the model with all the referred oral constituents (mucosa pellicle, salivary proteins, and HSC-3 cell line, HSCMuSp) when compared to the interaction with individual constituents, the PF + cells or PF + saliva. Regarding the procyanidins, a significant interaction was observed for the procyanidin monomer EcG, procyanidin dimers B7 and B2G, and trimer C1.

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.

Numerous monomeric and oligomeric flavanol sulfonation products were observed in 10 wines. Levels of 0.85-20.06 and 0-14.72 mg/L were quantified for two monomeric sulfonated flavan-3-ols and, surprisingly, were generally higher than the well-known native flavan-3-ol monomers. Increasing SO 2 levels during wine aging increased the sulfonate-modified flavan-3-ol monomers and dimers along with higher concentrations of native monomers. The results indicate that >10% of SO 2 is reacting with the C-4 carbocation, formed from acid cleavage of the interflavan bond, perhaps by a bimolecular S N 2-type reaction, and as a reducing agent. In addition, the high SO 2 wine had the lowest protein-binding tannin levels, tannin activity, and mean degree of polymerization (mDP), and acidic SO 2 treatment of condensed tannin abolishes protein binding. Thus, SO 2 changes tannin composition during wine aging, and the substantial formation of sulfonate-modified flavan-3-ols may provide an additional explanation for the reduction in astringency of aged red wines.

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 (EC 50 ) 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 paper reports the main trends and perspectives related to the current understanding of the relationships between saliva and flavor perception. Saliva is a key factor in flavor perception and controls the transport of flavor molecules to their receptors, their adsorption onto the mouth surfaces (i.e., oral mucosa), their metabolism by enzymatic modification, and the friction force in the oral cavity. The proteins in free saliva or in the mucosal pellicle contribute to flavor perception by interacting with or metabolizing flavor compounds. Most of these reactions were observed when using fresh whole saliva; however, they were absent or less frequently observed when using artificial saliva or depleted/frozen whole saliva. There is a need to better understand the role of protein aggregates in flavor perception. Within humans, there is great interindividual variation in salivary composition, which has been related to differences in flavor perception. However, the relative role of salivary proteins and the microbiota should be deeply investigated together with the impact of their composition on individual perception during life. Finally, future results must also consider cross-modal interactions at the brain level.

Activity-guided fractionation in combination with the taste dilution analysis, followed by liquid chromatography-tandem mass spectrometry and nuclear magnetic resonance experiments, led to the identification of 10 polymethoxylated flavones (PMFs), 6 limonoid glucosides, and 2 limonoid aglycones as the key bitterns of orange juice. Quantitative studies and calculation of dose-over-threshold factors, followed by taste re-engineering, demonstrated for the first time 25 sensometabolites to be sufficient to reconstruct the typical taste profile of orange juices and indicated that not a single compound can be considered a suitable marker for juice bitterness. Intriguingly, the taste percept of orange juice seems to be created by a rather complex interplay of limonin, limonoid glucosides, PMFs, organic acids, and sugars. For the first time, sub-threshold concentrations of PMFs were shown to enhance the perceived bitterness of limonoids. Moreover, the influence of sugars on the perceived bitterness of limonoids and PMFs in orange juice relevant concentration ranges was quantitatively elucidated.

Sensory profile, flavonols, proanthocyanidins, sugars, and organic acids were investigated in purees of six sea buckthorn (Hippophaë rhamnoides) cultivars. The sensory profiles of the purees were dominated by intense sourness followed by astringency and bitterness due to the high content of malic acid. Malic acid and isorhamnetin glycosides, especially isorhamnetin-3-O-sophoroside-7-O-rhamnoside, had close association with the astringent attributes in the different purees, whereas some of the known astringent compounds such as proanthocyanidin dimers and trimers or quercetin glycosides, had less impact. Moreover, the ratios between contents of acids and phenolic compounds were more important predictors of bitterness than the individual variables alone. Astringency and bitterness are important sensory factors for the consumer acceptance of sea buckthorn products. The current study provides new knowledge on the correlations between sensory properties and composition and supports industrial utilization of the sea buckthorn berries.

The transpeptidase activity of glutaminase from Bacillus amyloliquefaciens (GBA) and Aspergillus oryzae (GAO) to yield γ-[Glu] n -Phe peptides were verified for the first time. In the presence of Gln and Phe, γ-Glu-Phe and γ-Glu-γ-Glu-Phe were synthesized by GAO, and γ-Glu-Phe, γ-Glu-γ-Glu-Phe, γ-Glu-γ-Glu-γ-Glu-Phe, γ-Glu-γ-Glu-γ-Glu-γ-Glu-Phe, and γ-Glu-γ-Glu-γ-Glu-γ-Glu-γ-Glu-Phe were synthesized by GBA. The K m values for the transpeptidation catalyzed by GBA and GAO were 47.88 and 153.92 mM (Phe as the acceptor), 84.89 and 236.47 mM (γ-Glu-Phe as the acceptor), indicating that GBA had a greater affinity than GAO for Phe and γ-Glu-Phe in the transpeptidation reaction. The K m values for the transpeptidation catalyzed by GBA against acceptors, Phe and γ-[Glu] (1≤n<5) -Phe (47.88-206.47 mM), increased with an elevated number of γ-glutamyl residue within the acceptor. The optimal conditions for γ-[Glu] n -Phe synthesis were pH 10 and 37 °C for 3 h, 300 mM Gln, 100 mM Phe, 0.05 U/mL GBA. All the γ-[Glu] (1≤n≤5) -Phe exhibited astringency in water and imparted a kokumi taste to commercial soy sauce and model chicken broth. The astringent threshold values (2.5-3.92 mM) were approximately 3-fold of the kokumi threshold concentrations (0.78-1.53 mM). γ-[Glu] n -Phe or the post-enzymatic reaction mixture enhanced the umami intensity of commercial soy sauce and model chicken broth.

The interactions between salivary proteins and wine flavanols (catechin, epicatechin, and mixtures thereof) have been studied by HPLC-DAD, isothermal titration microcalorimetry, and molecular dynamics simulations. Chromatographic results suggest that the presence of these flavanol mixtures could facilitate the formation of precipitates to the detriment of soluble aggregates. Comparison between the thermodynamic parameters obtained showed remarkably higher negative values of ΔG in the system containing the mixture of both flavanols in comparison to the systems containing individual flavanols, indicating a more favorable scenario in the mixing system. Also, the apparent binding constants were higher in this system. Furthermore, molecular dynamics simulations suggested a faster and greater cooperative binding of catechin and epicatechin to IB7 14 peptides when both types of flavanols are present simultaneously in solution.

The interaction between phenolic compounds and salivary proteins is highly related to the astringency perception. Recently, it has been proven the existence of synergisms on the perceived astringency when phenolic acids were tested as mixtures in comparison to individual compounds, maintaining constant the total amount of the stimulus. The interactions between wine phenolic acids and the peptide fragment IB7 12 have been studied by saturation-transfer difference (STD) NMR spectroscopy. This technique provided the dissociation constants and the percentage of interaction between both individual and mixtures of hydroxybenzoic and hydroxycinnamic acids and the model peptide. It is noteworthy that hydroxybenzoic acids showed higher affinity for the peptide than hydroxycinnamic acids. To obtain further insights into the mechanisms of interaction, molecular dynamics simulations have been performed. Results obtained not only showed the ability of these compounds to interact with salivary proteins but also may justify the synergistic effect observed in previous sensory studies.

The interaction of astringent substances with salivary proteins, which results in protein precipitation, is considered a key event in the molecular mechanism underlying the oral sensation of puckering astringency. As the chemical nature of orally active astringents is diverse and the knowledge of their interactions with salivary proteins rather fragmentary, human whole saliva samples were incubated with suprathreshold and isointensity solutions of the astringent polyphenol (-)-epigallocatechin gallate, the multivalent metal salt iron(III) sulfate, the amino-functionalized polysaccharide chitosan, and the basic protein lysozyme. After separation of the precipitated proteins, the proteins affected by the astringents were identified and relatively quantified for the first time by complementary bottom-up and top-down mass spectrometry-based proteomics approaches. Major salivary target proteins, which may be involved in astringency perception, are reported here for each astringent stimulus.

In red winemaking, the extractability of condensed tannins (CT) can vary considerably even under identical fermentation conditions, and several explanations for this phenomenon have been proposed. Recent work has demonstrated that grape pathogenesis-related proteins (PRPs) may limit retention of CT added to finished wines, but their relevance to CT extractability has not been evaluated. In this work, Vitis vinifera and interspecific hybrids (Vitis ssp.) from both hot and cool climates were vinified under small-scale, controlled conditions. The final CT concentration in wine was well modeled from initial grape tannin and juice protein concentrations using the Freundlich equation (r 2 = 0.686). In follow-up experiments, separation and pretreatment of juice by bentonite, heating, freezing, or exogenous tannin addition reduced protein concentrations in juices from two grape varieties. The bentonite treatment also led to greater wine CT for one of the varieties, indicating that prefermentation removal of grape protein may be a viable approach to increasing wine CT.

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.

The aim of this paper is to study the real influence of seeds and stems on wine composition, astringency, and bitterness. A decolored grape juice and a grape juice macerated for 4 days from the same Cabernet Sauvignon grapes were fermented with or without supplementation with 100% seeds, 300% seeds, or 100% stems. Once alcoholic fermentation had finished, the wines were analyzed and tasted. The presence of seeds and stems increased the concentration of flavan-3-ol monomers with respect to the controls. However, the seeds mainly released (+)-catechin and (-)-epicatechin, whereas the stems mainly released (+)-catechin and (+)-gallocatechin. The seeds and stems also released proanthocyanidins; those from seeds have a lower mDP and a high percentage of galloylation, whereas those from stems have a higher mDP and a relatively high percentage of prodelphinidins. The presence of seeds and stems brought about a slight but significant increase in pH and lowered titratable acidity and ethanol content. The presence of seeds boosted color intensity, whereas stems had the opposite effect. Finally, both seeds and stems increased wine astringency and bitterness.

Black currant juices from five different cultivars were analyzed for composition, content, and mean degree of polymerization (mDP) of proanthocyanidins (PA) by UPLC-MS/MS. Juices contained both procyanidins (PC) and prodelphinidins (PD), but the PC-% varied significantly, from 28 to 82% of the total PA. In addition, high PD-% was related to high mDP and total PA content. Enzyme-assisted processing increased significantly total PA (5-14-fold), PD-% (12-65%), and mDP (1.8-6.2-fold) in the juices of all cultivars. Enzymatic treatment increased the contents of large PAs more than those of small PAs. The contents of PA and mDP were positively associated with the mouth-drying and puckering astringent characteristics. However, the PA content did not contribute to the bitter taste. Juices from the most bitter cultivars had the lowest contents of proanthocyanidins regardless of the processing method. This finding indicates the existence of other bitter compounds in black currants in addition to PA.

Polyphenols and maturity parameters were determined in 20 apple cultivars with potential for hard cider production grown in Virginia, U.S.A. Concentrations of five classes of polyphenols were significantly different across cultivar for both peel and flesh. Total polyphenol concentration ranged from 0.9 μg/g wwb in flesh of Newtown Pippin to 453 μg/g wwb in peel of Red Delicious. Harrison, Granny Smith, Rome, Winesap, and Black Twig cultivars contained the highest concentration of total flavan-3-ols in flesh, indicating potential to impart desired astringency and bitterness to cider under processing conditions where extraction of polyphenols from peel is minimal. These results can inform selection of fruit juice, extracts, and byproducts for investigations of bioactivity and bioavailability of polyphenols, and provide baseline data for horticultural and processing research supporting the growing hard cider industry in Virginia. Based on these data, cultivars Harrison, Granny Smith, Rome, Winesap, and Black Twig show high potential for cider production in Virginia.

Several factors could influence the tannin-protein interaction such as the human salivary protein profile, the tannin tested, and the tannin/protein ratio. The goal of this study aims to study the effect of different salivas (A, B, and C) and different tannin concentrations (0.5 and 1 mg/mL) on the interaction process as well as the complex's stability over time. This study is focused on the identification of new procyanidin B3-human salivary protein complexes. Thus, 48 major B3-human salivary protein aggregates were identified regardless of the saliva and tannin concentration tested. A higher number of aggregates was found at lower tannin concentration. Moreover, the number of protein moieties involved in the aggregation process was higher when the tannin concentration was also higher. The selectivity of the different groups of proteins to bind tannin was also confirmed. It was also verified that the B3-human salivary protein complexes formed evolved over time.

The general accepted mechanism for astringency arises from the interaction between tannins and salivary proteins (SP) resulting in (in)soluble aggregates. By HPLC analysis, it was observed that repeated sips of procyanidins (PC) solution practically depleted aPRPs (∼14%) and statherin (∼2%), and significantly reduced the amount of gPRPs. On the other hand, bPRPs were not significantly affected. In the analysis performed after the last exposure to PC solution, it was seen a significant recovering of the chromatographic peaks corresponding especially to aPRPs (∼74%) and statherin (∼80%). In vitro interaction between SP and PC results in the decrease of the chromatographic peaks of aPRPs and statherin, suggesting that these proteins were involved in the formation of a significant quantity of insoluble complexes. In general, the results suggest that the different families of SP can be involved in different stages of the development of astringency sensation.