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The astringency of green tea is an integrated result of the synergic and antagonistic effects of individual tea components, whose mechanism is highly complex and not completely understood. Herein, we used an epigallocatechin gallate (EGCG)/caffeine (CAF)/saliva model to simulate the oral conditions during tea drinking. The effect of CAF on the interaction between EGCG and salivary proteins was first investigated using molecular docking and isothermal titration calorimetry (ITC). Then, the rheological properties and the micro-network structure of saliva were studied to relate the molecular interactions and perceived astringency. The results revealed that CAF partially occupied the binding sites of EGCG to salivary proteins, inhibiting their interaction and causing changes in the elastic network structure of the salivary film, thereby reducing astringency., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

Ionic valency influences oral processing by changing salivary behavior and merits more attention since little is known. In this study, the influence of three ionic valences (monovalent, divalent and trivalent), ionic strength and epigallocatechin gallate (EGCG) on lubricating properties of saliva were investigated. Tribological measurements were used to characterize the lubrication response of KCl, MgCl 2 , FeCl 3 , and AlCl 3 in combination with EGCG to the ex vivo salivary pellicle. KCl at 150 mM ionic strength provided extra lubrication via hydration lubrication. Contrarily, trivalent salts aggregated together with the salivary mucins via ionic cross-link interactions, which led to a decrease in salivary lubrication. FeCl 3 and AlCl 3 affected the salivary lubrication differently, which was attributed to changes in the pH. Finally, in presence of EGCG, FeCl 3 interacted with EGCG via chelating interactions, preventing salivary protein aggregation. This resulted in less desorption of the salivary film, retaining the lubrication ability of salivary proteins., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)

Astringency is an important mouthfeel attribute that influences the sensory experiences of many food and beverage products. While salivary lubricity loss and increased oral friction were previously believed to be the only astringency mechanisms, recent research has demonstrated that nontactile oral receptors can trigger astringency by responding to astringents without mechanical stimulation. Various human factors have also been identified that affect individual responses to astringents. This article presents a critical review of the key research milestones contributing to the current understanding of astringency mechanisms and the instrumental approaches used to quantify perceived astringency intensity. Although various chemical assays or physical measures mimic in-mouth processes involved in astringent mouthfeel, this review highlights how one chemical or physical approach can only provide a single measure of astringency determined by a specific mechanism. Subsequently, using a single measurement to predict astringency perception is overly idealistic. Astringency has not been quantified beyond the loss of saliva lubrication; therefore, nontactile receptor-based responses must also be explored. An important question remains about whether astringency is a single perception or involves distinct sub-qualities such as pucker, drying, and roughness. Although these sub-quality lexicons have been frequently cited, most studies currently view astringency as a single perception rather than dividing it into sub-qualities and investigating the potentially independent mechanisms of each. Addressing these knowledge gaps should be an important priority for future research., (© The Author(s) 2024. Published by Oxford University Press. All rights reserved. For commercial re-use, please contact reprints@oup.com for reprints and translation rights for reprints. All other permissions can be obtained through our RightsLink service via the Permissions link on the article page on our site—for further information please contact journals.permissions@oup.com.)

In-mouth interaction of red wine compounds with salivary proteins is a primary event allegedly responsible for eliciting the mouth-feel sensation of astringency. Those interactions have been currently associated with precipitation of salivary protein/polyphenol complexes. However, such single physicochemical evidence for interaction does not account for the complexity of astringency. This study aimed to develop a paper chromatography method to assess interactions between red wine and the salivary protein fraction using stepwise series of red wine/saliva binary mixtures from 100% wine to 100% saliva ("Alpha and Omega series"). Aliquots of each one of the mixtures were spotted on a cellulose membrane to scrutinize independently the distribution areas of wine components (naturally pink-colored) and salivary protein (stained blue in Coomassie Brilliant R-250). This double target detection revealed interactions between saliva and red wine components along most of the quantitative Alpha and Omega series, a point of equivalence corresponding to maximum interactivity for both complex reactants and a non-diffusible sub-fraction of saliva displaying the highest interactivity. The results indicate a novel way to assess quantitatively physicochemical interactions between red wines and human saliva but also provide new lights to approach the identification of molecular salivary structures involved in triggering astringency., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023. Published by Elsevier B.V.)

Astringency is an important sensory characteristic of food and beverages containing polyphenols. However, astringency perception in elderly people has not been previously documented. The aim of the present work was to evaluate sensitivity to astringency as a function of age, salivary flow and protein amount. Fifty-four panellists, including 30 elderly people (age = 75 ± 4.2 years) and 24 young people (age = 29.4 ± 3.8 years), participated in this study. Astringency sensitivity was evaluated by the 2-alternative forced choice (2-AFC) procedure using tannic acid solutions. Whole saliva was collected for 5 min before and after the sensory tests. The results showed that the astringency threshold was significantly higher in the elderly group than the young group. No correlation was observed between the salivary protein amount and threshold value. However, a negative correlation between salivary flow and threshold was observed in the young group only. These results showed a difference in oral astringency perception as a function of age. This difference can be linked to salivary properties that differ as a function of age.

Salivary proteins have the potential to alter oral sensory perception of foods. In rodents, dietary polyphenol exposure increases salivary concentrations of polyphenol-binding proteins and several cystatins, which correlate with less aversion to polyphenol-rich solutions. If similar salivary shifts occur in humans, then increasing dietary polyphenols may improve orosensory experience of polyphenol-rich foods. We hypothesized that small dietary changes, focused on polyphenols, would increase expression of salivary binding proteins for polyphenols and thus suppress unpleasant polyphenol sensations. However, analogs of salivary polyphenol-binding proteins are found in foods. Thus, we also hypothesized that food-sourced analogs of these salivary proteins would mitigate changes in saliva and sensation. Human subjects (N=55) alternated weeks of consuming a low polyphenol diet and then a regular diet plus a polyphenol-rich chocolate milk (almond, containing no polyphenol-binding proteins, or bovine, containing polyphenol-binding proteins). Statistical analyses revealed both chocolate milk interventions corresponded to changes in relative expression of 96 proteins and calculated concentration of 146 proteins (both after correction for false discovery rate), out of 1,176 proteins identified through proteomics. Of the proteins that changed, proline-rich proteins and cystatins were noticeable, which reflects prior work in animal studies. Subjects rated all chocolate milks as less flavorful after the bovine chocolate milk intervention week compared to low polyphenol weeks, but generally sensory changes were minimal. However, the results confirm that dietary changes coincide with salivary changes, and that some of those changes occur in proteins that have potential to influence oral sensations., (Copyright © 2020 Elsevier Inc. All rights reserved.)

Astringency is a complex oral sensation, commonly experienced when dietary polyphenols interact with salivary proteins. Most astringent stimuli alter protein levels, which then require time to be replenished. Although it is standard practice in astringency research to provide breaks in between stimuli, there is limited consensus over the amount of time needed to restore the oral environment to baseline levels. Here we examined salivary protein levels after exposure to 20 mL of a model stimulus (cranberry polyphenol extract, 0.75 g/L CPE) or unsweetened cranberry juice (CJ), over a 10 min period. Whole saliva from healthy subjects ( n = 60) was collected at baseline and after 5 and 10 min following either stimulus. Five families of proteins: basic proline-rich proteins (bPRPs); acidic proline-rich proteins (aPRPs); histatins; statherin; and S-type cystatins, were analyzed in whole saliva via HPLC-low resolution-ESI-IT-MS, using the area of the extracted ion current (XIC) peaks. Amylase was quantified via immunoblotting. In comparison to baseline (resting), both stimuli led to a rise in levels of aPRPs ( p < 0.000) at 5 min which remained elevated at 10 min after stimulation. Additionally, an interaction of PROP taster status and time was observed, wherein super-tasters had higher levels of amylase in comparison to non-tasters after stimulation with CJ at both timepoints ( p = 0.014-0.000). Further, male super-tasters had higher levels of bPRPs at 5 min after stimulation with both CJ and CPE ( p = 0.015-0.007) in comparison to baseline. These data provide novel findings of interindividual differences in the salivary proteome that may influence the development of astringency and that help inform the design of sensory experiments of astringency.

Wine sensory sessions normally involve the tasting of several samples, to remove food residues from the mouth the use of palate cleansers (PC) is needed. Until now, there is no agreement on the best PC to use during wine tasting sessions. The aim of this work is to study the relationship between the components retained in saliva after wine tasting and the remnant sensory feeling (astringency, alcohol, and acidity). For that, different common PC (water, carbonated water, and milk) were tested and saliva samples (expectorated and scraped) from nine trained panelists were collected after wine with and without PC trials. Results showed that after palate cleansing and not cleansing, astringency, alcoholic and acidity perception were influenced by time, PC and panelist. Astringency perception showed the greatest intensity in comparison to alcoholic and acidity. Milk was the only PC which reduced quantifiable polyphenols in expectorated saliva, as well as reducing astringency feelings. Although compositions of expectorated and scraped saliva correlated between them, polyphenols accumulated in the expectorated saliva significantly more. Retained polyphenols were correlated with astringency perception, but no correlation was found with salivary proteins. These findings assessed the astringency build-up effect during wine tasting due to polyphenols accumulation in saliva, remarking the importance of an adequate PC selection. All things considered, the present work confirmed the relationship between after-swallow mouthfeel perception and mouth residues instrumentally quantified. Also, milk has proven to be the most effective of the three PC. PRACTICAL APPLICATIONS: During tasting the accumulation of residues from previous wine samples tasted, could mislead the judgment of wine sensory qualities by oenologists. Therefore, between tasting samples it is highly important to choose the right PC. However, until now the selection of PC remains empirical, therefore in this work, we proposed to study the residues in saliva by using different PC and quantifying instrumentally, the wine residues. The methodology selected to quantify the wines residues in saliva was quick and easy to use. Furthermore, instrumental results were related with the sensory feeling of mouth cleanliness without considering individual panel member's preferences of PC. In this study, to remove astringency feeling, milk was shown to be the best cleanser in comparison with water, carbonated water or nothing, but oenologist/winemakers could use this instrumental methodology in saliva to select which one is the best among their current PC used., (© 2018 Wiley Periodicals, Inc.)

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.

Wine astringency was evaluated based on the interaction of two complex matrices (red wine and saliva) by combining localized surface plasmon resonance (LSPR) and molecular imprinted polymers (MIP) at gold nanodisks as an alternative to sensorial analysis. The main objective of the work was to simulate wine astringency inside the mouth by mimicking this biological system. The LSPR/MIP sensor provided a linear response for astringency expressed in pentagalloyl glucose (PGG) units in concentrations ranging from 1 to 140μmol/L. The sensor was also applied to wine samples correlating well with sensorial analysis obtained by a trained panel. The correlation of astringency and wine composition was also evaluated showing that anthocyanins may have an important role, not only for pigmentation but also in astringency., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

The addition of external phenolic compounds to wines in order to improve their sensory quality is an established winemaking practice. This study was aimed at evaluating the effect of the addition of quercetin 3-O-glucoside on the astringency and bitterness of wines. Sensory results showed that the addition of this flavonol to wines results in an increase in astringency and bitterness. Additionally, flavonol-human salivary protein interactions were studied using fluorescence spectroscopy, dynamic light scattering and molecular dynamic simulations (MD). The apparent Stern-Volmer (KsvApp) and the apparent bimolecular quenching constants (kqApp) were calculated from fluorescence spectra. The KsvApp was 12620±390M(-1), and the apparent biomolecular constant was 3.94×10(12)M(-1)s(-1), which suggests that a complex was formed between the human salivary proteins and quercetin 3-O-glucoside. MD simulations showed that the quercetin 3-O-glucoside molecules have the ability to bind to the IB937 model peptide., (Copyright © 2016 Elsevier Ltd. All rights reserved.)

Salivary protein difference value (SP D-value) is a quantitative measure of salivary protein replenishment, which reportedly relates to individual differences in perceived astringency. This in vitro measure is calculated as the difference in total salivary protein before (S1) and after (S2) stimulation with tannic acid, with a greater absolute value (S2-S1) indicating less protein replenishment. Others report that this measure predicts perceived astringency and liking of liquid model systems and beverages containing added polyphenols. Whether this relationship generalizes to astringent compounds other than polyphenols, or to solid foods is unknown. Here, the associations between SP D-values and perceived astringency and overall liking/disliking for alum and tannic acid (experiment 1) as well as solid chocolate-flavored compound coating with added tannic acid or grape seed extract (GSE) (experiment 2) were examined. In both experiments, participants (n=84 and 81, respectively) indicated perceived intensity of astringency, bitterness, sweetness, and sourness, and degree of liking of either aqueous solutions, or solid chocolate-flavored compound coating with added astringents. Data were analyzed via linear regression, and as discrete groups for comparison to prior work. Three discrete groups were formed based on first and third quartile splits of the SP D-value distribution: low (LR), medium (MR), and high responding (HR) individuals. In experiment 1, significantly higher mean astringency ratings were observed for the HR as compared to the LR/MR groups for alum and tannic acid, confirming and extending prior work. In experiment 2, significantly higher mean astringency ratings were also observed for HR as compared to LR groups in solid chocolate-flavored compound containing added tannic acid or GSE. Significant differences in liking were found between HR and LR groups for alum and tannic acid in water, but no significant differences in liking were observed for chocolate-flavored compound samples. A significant linear relationship between SP D-values and perceived astringency was observed for both alum and tannic acid (p's<0.001), although the variance explained was relatively low (R(2)=0.33 and 0.29, respectively). In the solid chocolate-flavored compound spiked with either tannic acid or GSE, the relationship was not significant (p=0.17 and 0.30; R(2)=0.03 and 0.02, respectively). Due to the weak associations overall, and the lack of significant differences in perception of astringency between the MR and LR groups, we conclude that SP D-values are not a strong predictor of astringency, especially in solid, high-fat foods. Additional research investigating alternative methods for quantifying individual differences in astringency, as well as exploring the underlying complexities of this percept appears warranted., (Copyright © 2016 Elsevier Inc. All rights reserved.)

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.

The objective of this study was to investigate the influence of tannins and gallic acid on the salivary lubrication behavior. Furthermore, the effects of pH and mannoproteins in combination with gallic acid on the lubrication of saliva were studied. The addition of gallic acid and tannins were found to increase friction caused by the removal of the saliva film. Tannins resulted in higher friction compared to gallic acid. Lowering pH increased friction of gallic acid mixtures with saliva, due to stronger interactions between gallic acid and saliva. The increased friction caused by gallic acid was inhibited by the addition of mannoproteins due to the hydrogen bond interactions between gallic acid and mannoproteins, thereby decreasing the complex formation between gallic acid and salivary proteins. A correlation of 0.96 was found between the hydrodynamic diameter of the aggregate and the delta friction suggesting that the formation of aggregates determined the lubrication behavior.

Objective: This study aimed to understand the astringency perception difference and formation mechanism of different varieties of Chrysanthemum tea during drinking, and provide new research ideas and theoretical basis for the astringency perception and sensory research of edible flowers. Methods: 5 different varieties of Chrysanthemum were selected to determined the main astringent chemical constituents by UV-Vis spectrophotometry. The perceiving intensity of the astringency of five different varieties of Chrysanthemum was measured and evaluated by using the intelligent taste analysis system of electronic tongue and the traditional sensory evaluation method. The interaction between the main astringent chemical constituents in Chrysanthemum and saliva BCA method was analyzed by SDS-PAGE method, Coomassie bright blue method and fluorescence spectrophotometer method. Results: Among the five kinds of Chrysanthemum, emperor Chrysanthemum and Bozhou Chrysanthemum had the highest content of polyphenols and flavonoids, and the corresponding characteristic value of astringency was also the strongest. The content of polyphenols and flavonoids was positively correlated with the astringency intensity of the Chrysanthemum tea. Conclusion: As the main astringent substance, the difference of polyphenols and flavonoids in different varieties of Chrysanthemum tea significantly affects the astringent taste, and the astringent substance in Chrysanthemum tea combines with proteins in saliva and precipitates, which is one of the main reasons for astringent.

Interactions between food and saliva govern complex mouthfeel perceptions such as astringency. Herein, we present a study of the interactions of salivary proteins with the main pea protein fractions that are obtained by isoelectric and salt precipitation (legumin-rich, vicilin-rich and albumin-rich fractions). The sensory evaluations performed on protein solutions by trained panelists evidenced that all three protein fractions exhibit a basal level of astringency, but that the albumin fraction was perceived as the most astringent one. All three fractions induced significant but comparable loss of salivary lubrication. Yet, when compared to the other fractions, the albumin fraction showed the formation of a thicker and more rigid film on salivary conditioning film-coated sensors as measured using a quartz crystal microbalance with dissipation monitoring (QCM-D). We also present proteomics studies on the precipitates obtained from the mixtures of saliva and pea protein fractions. Protein identification finds a pool of salivary proteins involved in non-specific interactions with all the three pea protein fractions. Yet, 13 pea proteins specific to the albumin fraction were identified as being involved in specific interactions with salivary proteins. Several of these proteins are part of the plant defense mechanisms and are likely to interact with many salivary proteins. This could explain the higher number of salivary proteins found in the precipitate induced by the albumin fraction when compared to the other two. These quantitative results increase the understanding of the complex links between plant protein-salivary protein interactions and astringency. [Display omitted] • The albumin pea protein fraction was the most astringent pea protein fraction. • Globulin and albumin pea proteins induced a similar salivary lubrication breakdown. • Albumin pea proteins formed a rigid and thick film on a salivary pellicle. • 13 pea proteins of the albumin fraction are likely to trigger interactions with saliva. [ABSTRACT FROM AUTHOR]

Astringency is an important sensory characteristic of food and beverages containing polyphenols. However, astringency perception in elderly people has not been previously documented. The aim of the present work was to evaluate sensitivity to astringency as a function of age, salivary flow and protein amount. Fifty-four panellists, including 30 elderly people (age = 75 ± 4.2 years) and 24 young people (age = 29.4 ± 3.8 years), participated in this study. Astringency sensitivity was evaluated by the 2-alternative forced choice (2-AFC) procedure using tannic acid solutions. Whole saliva was collected for 5 min before and after the sensory tests. The results showed that the astringency threshold was significantly higher in the elderly group than the young group. No correlation was observed between the salivary protein amount and threshold value. However, a negative correlation between salivary flow and threshold was observed in the young group only. These results showed a difference in oral astringency perception as a function of age. This difference can be linked to salivary properties that differ as a function of age.

Astringency, a sensory characteristic of food and beverages rich in polyphenols, mainly results from the formation of complexes between polyphenols and salivary proteins, causing a reduction of the lubricating properties of saliva. To develop an in vitro assay to estimate the astringency of oolong tea infusion, artificial oil bodies were constituted with sesame oil sheltered by a modified caleosin fused with histatin 3, one of the human salivary small peptides. Aggregation of artificial oil bodies was induced when they were mixed with oolong tea infusion or its major polyphenolic compound, (-)-epigallocatechin gallate (EGCG) of 100µM as observed in light microscopy. The aggregated artificial oil bodies gradually floated on top of the solution and formed a visible milky layer whose thickness was in proportion to the concentrations of tea infusion. This assay system was applied to test four different oolong tea infusions with sensory astringency corresponding to their EGCG contents. The result showed that relative astringency of the four tea infusions was correlated to the thickness of floated artificial oil bodies, and could be estimated according to the standard curve generated by simultaneously observing a serial dilution of the tea infusion with the highest astringency. [ABSTRACT FROM AUTHOR]

Oral tribology is emerging as a new paradigm to quantify friction and lubrication of food-saliva mixtures in the oral mucosa. Recently, oral tribology has captured research attention in quantifying wine astringency, a characteristic ‘dryness feeling’, which strongly impacts consumer preference. Hence, this paper aims to provide a concise review of oral tribology in the context of wine astringency. Firstly, the important roles of ‘biolubricant’ saliva, salivary proteins and current tribo-pairs used in oral tribology measurements are reviewed. Then, we have discussed the key mechanisms of wine astringency involving polyphenol-salivary protein interactions (hydrogen bonding, hydrophobic interactions), rupture of the lubricating salivary film and oral sensation of discrete particles. Studies employing Stribeck curve analysis and microstructural characterisation to understand polyphenol-salivary protein interactions are reviewed. Finally, we highlighted the need for bio-relevant tribo-pairs, simulated oral conditions and tribology-sensory correlation, before such quantification can be used to characterise wine astringency at a commercial level. [ABSTRACT FROM PUBLISHER]

Nine Saccharomyces cerevisiae cultures, isolated from different sources, were tested for their ability to reduce tannins reactive towards salivary proteins, and potentially responsible for wine astringency. Strains were preliminary genetically characterized and evaluated for physiological features of technological interest. Laboratory-scale fermentations were performed in three synthetic media: CT) containing enological grape tannin; CTP) CT supplemented with organic nitrogen sources; CTPV) CTP supplemented with vitamins. Adsorption of total tannins, tannins reactive towards salivary proteins, yellow pigments, phenolics having antioxidant activity, and total phenols, characterizing the enological tannin, was determined by spectrophotometric methods after fermentation. The presence of vitamins and peptones in musts greatly influenced the adsorption of tannins reactive towards salivary proteins (4.24 g/L gallic acid equivalent), thus promoting the reduction of the potential astringency of model wines. With reference to the different phenolic classes, yeast strains showed different adsorption abilities. From a technological point of view, the yeast choice proved to be crucial in determining changes in gustative and mouthfeel profile of red wines and may assist winemakers to modulate colour and astringency of wine. [ABSTRACT FROM AUTHOR]

A simulated maceration was carried out with skins or seeds of Aglianico, Merlot and Cabernet Sauvignon grape cultivars in order to study the entity of the transfer of tannins from grape to wine. The structural characteristics of skins and seeds extracts (native tannins) and corresponding wine-like solutions (macerated tannins) were analysed by phloroglucinolysis. Their potential astringency was evaluated according to the reactivity towards salivary proteins by the Saliva Precipitation Index (SPI). From grape to wine-like solution, the transfer of structural characteristics varied differently for skins and seeds. A significant influence of extraction method and grape variety was also stated, principally as regard the percentage of prodelphinidins (%P) for skins, and of galloylation (%G) for seeds. For some parameters that were able to differentiate grapes through the maceration process, a cultivar effect emerged. Reactivity of tannins also differed, but not for seeds. For Aglianico native and macerated tannins, the highest in SPIs, seeds monomers and oligomers were quantified by HPLC/MS. Principal Component Analysis (PCA) allowed to reveal the structural characteristics mainly associated with the reactivity of tannins towards salivary proteins. The proanthocyanidins content and the %G increased potential astringency, while it was reduced by the %P. [ABSTRACT FROM AUTHOR]

Chitosan is a biopolymer that can be used in food applications such as forming edible coatings and nanoparticles. It is a linear polysaccharide composed of neutral (acetylated) and positively (deacetylated) sugar units and can be prepared with varying content of the two units. One factor limiting the use of chitosan is causing an unacceptable level of astringency. We hypothesized that astringency was related to the positive charge density and that decreasing the charge density would decrease astringency. Chitosans with fraction of acetylated units (F A ) ranging from 0.01 to 0.49 (percentage degree of acetylation from 1 to 49) were analyzed for astringency using a time intensity sensory method. In addition, the ability of chitosans to precipitate saliva proteins was determined. Increasing F A from 0.01 to 0.49 caused a decrease in maximum astringency sensation from 10.9 to 7.2. Mucins and other saliva proteins were precipitated by chitosans but a simple association with astringency intensity was not observed. It can be concluded that altering the charge density of chitosans is a means to alter chitosan astringency. [ABSTRACT FROM AUTHOR]

Astringency is described as a 'dry puckering-like sensation' in the mouth following consumption of tannins including tea polyphenols. The current model describing astringency is based on precipitation of salivary proline-rich proteins by polyphenols and/or altered salivary lubrication. Because dryness from astringency is detected by oral tissues this suggests other interactions, possibly through direct alteration of the lubricating mucosal pellicle, which may also expose the oral mucosa below. A loss of mucosal lubrication is likely to be fundamental in astringency development and it seems likely that astringent stimuli alter the salivary bulk, saliva rheology and the saliva pellicle leading to an increase of friction in the oral cavity. Practical Applications For the consumer, high levels of astringency in foods may lead to them becoming unpalatable. However, as the health benefits of many plant-based astringent molecules, such as polyphenols, have become more apparent there is a desire to increase their levels in the diet. Currently, because of the complexity of astringency and the likelihood of multiple mechanisms occurring simultaneously, there is still a gap in knowledge regarding how these mechanisms affect each other and how these lead to altered mouthfeel after consumption of astringent stimuli. A good understanding of astringency development in the oral cavity may lead to an advancement of mechanisms that may prevent the astringency without reducing levels of the astringent molecules in food. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this work was to evaluate the astringency of red wines by means of a SDS–PAGE based-method. The optimization of the in vitro assay, named SPI (Saliva Precipitation Index) that measured the reactivity of salivary proteins towards wine polyphenols, has been performed. Improvements included the choice of saliva:wine ratio, saliva typology (resting or stimulated saliva), and temperature of binding. The LOD (0.05g/L of condensed tannin) and LOQ (0.1g/L of condensed tannin) for the binding reaction between salivary proteins and tannins added in white wine were also determined. Fifty-seven red wines were analysed by the optimised SPI, the Folin–Ciocalteu Index, the gelatine index, the content of total tannins and the sensory quantitative evaluation of astringency. A significant correlation between the SPI and the astringency of red wines was found (R 2 =0.969), thus indicating that this assay may be useful as estimator of astringency. [Copyright &y& Elsevier]

Grape seed and skin proanthocyanidins undergo significant changes during grape maturation. Those changes have been associated with a decreased astringency of grapes collected at later maturation stages. We have now compared the ability of proanthocyanidin-rich extracts from Carménère grape seeds collected at two stages of berry development (veraison vs. harvest) both to interact with salivary proteins and to produce astringency. Interaction of proanthocyanidins with the salivary protein was assessed by analysing the concentration-dependent effect of seed extracts both on inducing salivary protein precipitation and on restricting diffusion of the salivary protein on cellulose membranes. Seed extracts from grapes collected at veraison compared with those of grapes collected at harvest displayed a higher ability both to interact with the salivary protein fraction and to produce astringency. As a whole, our observations show that astringency is closely dependent on the magnitude of the interactions between proanthocyanidins and the salivary protein fraction. [ABSTRACT FROM AUTHOR]

Astringency, a tactile sensation felt in the mouth after exposure to various foods, is poorly understood. Our objective was to investigate the mechanism of astringency by determining if it was related to a loss of saliva's ability to lubricate mouth surfaces. We used 2 complementary approaches: (1) instrumentally determining if astringents decrease salivary lubricity and (2) determining if human subjects could perceive these changes. Instrumentally measured friction of saliva-tannin mixtures was greater than that of saliva-water mixtures, but these differences were not detectable by human subjects. Adding alum or acid to saliva did not increase friction measured either instrumentally or by human subjects rubbing the mixture between their thumb and fingers. Thus a loss of salivary lubricity is likely not a central mechanism of astringency. Practical Applications: If astringency's mechanism can be elucidated, food producers will gain knowledge that will enable them to manufacture, alter, or treat the food in a way to retain its healthful attributes while minimizing the astringency. This knowledge will also benefit sensory scientists interested in the intensity perceptions of the sensations and will allow them to devise improved methods for the assessment of the attribute. [ABSTRACT FROM AUTHOR]

Abstract: The effect of β-lactoglobulin (β-LG) at pH 3.5 and 7.0 on lubricating property of saliva as related to astringency perception was investigated using tribology. Saliva was adsorbed onto surfaces of a rotating poly dimethylsiloxane (PDMS) ball and disc to form a film under conditions that mimic the rubbing contacts in the oral cavity () and the lubricity of saliva films upon exposure to astringent compounds was measured. While addition of non-astringent β-LG at pH 7.0 slowly increased friction of saliva film between tribopair surfaces, β-LG at pH 3.5 rapidly increased the friction coefficients of saliva, similar to other astringent compounds (epigallocatechin gallate and alum). This supports the hypothesis that astringency of β-LG arises from the loss of lubrication of saliva which is in agreement with the well-accepted astringency model of polyphenols. Increasing β-LG concentration at pH 3.5 (0.5–10% w/w) caused a rapid increase in friction coefficient; however, at the highest protein concentration, the friction coefficient, although higher than observed for water, was below the values observed for the lower protein concentrations. This suggests that static tribology testing is different from the dynamic in-mouth system such that a simple relationship between friction and sensory astringency cannot be found for all conditions. [Copyright &y& Elsevier]

Low molecular weight phenolic compounds (LMWP) contribute to astringency and bitterness, two important sensory attributes. This work aimed to study the interactions between human saliva and a group of LMWP from a grape seed extract, namely, monomers, dimers and trimers of flavan-3-ol plus gallic acid. LMWP in the sediment that was produced by mixing whole saliva with the grape seed extract were identified by high-performance liquid chromatography analysis (HPLC-DAD). Two assays to produce LMWP-salivary protein sediments were carried out. An indirect assay consisted of in vitro mixing aliquots of saliva with a constant volume of the grape seed extract followed by centrifugation and sediment analysis. In a direct assay, aliquots of the grape seed extract were mixed in-mouth with saliva, returned to a vessel and centrifuged. In each assay, polyphenol composition of the sediments varied according to the tannin/saliva vol/vol ratio although in both cases monomeric LMWP were the most abundant polyphenol components of the sediments. The study also suggested the need for a strict control of the in vitro experimental conditions used to mimic the in vivo conditions in which tannin-protein interactions do occur and produce astringency perception. [ABSTRACT FROM AUTHOR]

Previous studies suggest that different copper species formed in saliva have different reactivity in chemical reactions that may be associated with perception of metallic sensation occurring in the oral cavity. This study was performed to understand copper speciation in human saliva, which will help to understand the perception mechanism of metallic taste. Saliva samples were treated with CuSO·5HO at the levels of 0, 2.5, 10, 20, or 40 mg/L as Cu in vitro. Also saliva is collected before and after drinking 20 mL of 0, 2.5, and 5 mg/L copper in water (in vivo treatment). Copper speciation was operationally determined based on apparent molecular size using ultrafiltration coupled with inductively coupled plasma mass spectrometry. For in vitro copper treatment, 50-70% of copper was soluble at Cu ≤ 10 mg/L, whereas 60-70% of copper was in complex or insoluble form at Cu > 20 mg/L. For in vivo copper treatment, 90-95% of copper was soluble in saliva. These results suggest that copper is in the soluble unbound form in saliva at low concentrations. At higher concentrations, copper either becomes insoluble or binds with salivary components. [ABSTRACT FROM AUTHOR]

ingency is thought to result from the interaction between salivary proline-rich proteins (PRP) that belong to the intrinsically unstructured protein group (IUP), and tannins, which are phenolic compounds. IUPs have the ability to bind several and/or different targets. At the same time, tannins have different chemical features reported to contribute to the sensation of astringency. The ability of both electrospray ionization mass spectrometry and tandem mass spectrometry to investigate the noncovalent interaction occurring between a human salivary PRP, IB5, and a model tannin, epigallocatechin 3- O-gallate (EgCG), has been reported. Herein, we extend this method to study the effect of tannin chemical features on their interaction with IB5. We used five model tannins, epigallocatechin (EgC), epicatechin 3- O-gallate (ECG), epigallocatechin 3- O-gallate (EgCG), procyanidin dimer B2 and B2 3′- O-gallate, which cover the main tannin chemical features: presence of a gallate moiety (galloylation), the degree of polymerization, and the degree of B ring hydroxylation. We show the ability of IB5 to bind these tannins. We report differences in stoichiometries and in stability of the IB5•1 tannin complexes. These results demonstrate the main role of hydroxyl groups in these interactions and show the involvement of hydrogen bonds. Finally, these results are in line with sensory analysis, by Vidal et al. (J Sci Food Agric 83:564–573, 2003) pointing out that the chain length and the level of galloylation are the main factors affecting astringency perception. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Whey protein beverages are adjusted to pH <4.5 to enhance clarity and stability, but this pH level is also associated with increased astringency. The goal of this investigation was to determine the effects of protein concentration on astringency and interactions between whey and salivary proteins. Whey protein beverages containing 0.25 to 13% (wt/wt) β-lactoglobulin and 0.017% (wt/wt) sucralose at pH 2.6 to 4.2 were examined using descriptive sensory analysis. Controls were similar pH phosphate buffers at phosphate concentrations equivalent to the amount of phosphoric acid required to adjust the pH of the protein solution. Changes in astringency with protein concentration depended on pH. At pH 3.5, astringency significantly increased with protein concentration from 0.25 to 4% (wt/wt) and then remained constant from 4 to 13% (wt/wt). Conversely, at pH 2.6, astringency decreased with an increase in protein concentration [0.5-10% (wt/wt)]. This suggests a complex relationship that includes pH and buffering capacity of the beverages. Furthermore, saliva flow rates increased with increasing protein concentrations, showing that the physiological conditions in the mouth change with protein concentration. Maximum turbidity of whey protein-saliva mixtures was observed between pH 4.6 and 5.2. Both sensory evaluation and in vitro study of interactions between β-LG and saliva indicate that astringency of whey proteins is a complex process determined by the extent of aggregation occurring in the mouth, which depends on the whey protein beverage pH and buffering capacity in addition to saliva flow rate. [ABSTRACT FROM AUTHOR]

Whey proteins are a major ingredient in sports drink and functional beverages. At low pH, whey proteins are astringent, which may be undesirable in some applications. Understanding the astringency mechanism of whey proteins at low pH could lead to developing ways to minimize the astringency. This study compared the astringency of β-lactoglobulin (β-LG) at low pH with phosphate buffer controls having the same amount of phosphate and at similar pH. Results showed that β-LG samples were more astringent than phosphate buffers, indicating that astringency was not caused by acid alone and that proteins contribute to astringency. When comparing among various whey protein isolates (WPI) and lactoferrin at pH 3.5, 4.5, and 7.0, lactoferrin was astringent at pH 7.0 where no acid was added. In contrast, astringency of all WPI decreased at pH 7.0. This can be explained by lactoferrin remaining positively charged at pH 7.0 and able to interact with negatively charged saliva proteins, whereas the negatively charged WPI would not interact. Charge interactions were further supported by β-LG or lactoferrin and salivary proteins precipitating when mixed at conditions where β-LG, lactoferrin, or saliva themselves did not precipitate. It can be concluded that interactions between positively charged whey proteins and salivary proteins play a role in astringency of proteins at low pH. [ABSTRACT FROM AUTHOR]

Numerous protein–polyphenol interactions occur in biological and food domains particularly involving proline-rich proteins, which are representative of the intrinsically unstructured protein group (IUP). Noncovalent protein–ligand complexes are readily detected by electrospray ionization mass spectrometry (ESI-MS), which also gives access to ligand binding stoichiometry. Surprisingly, the study of interactions between polyphenolic molecules and proteins is still an area where ESI-MS has poorly benefited, whereas it has been extensively applied to the detection of noncovalent complexes. Electrospray ionization mass spectrometry has been applied to the detection and the characterization of the complexes formed between tannins and a human salivary proline-rich protein (PRP), namely IB5. The study of the complex stability was achieved by low-energy collision-induced dissociation (CID) measurements, which are commonly implemented using triple quadrupole, hybrid quadrupole time-of-flight, or ion trap instruments. Complexes composed of IB5 bound to a model polyphenol EgCG have been detected by ESI-MS and further analyzed by MS/MS. Mild ESI interface conditions allowed us to observe intact noncovalent PRP–tannin complexes with stoichiometries ranging from 1:1 to 1:5. Thus, ESI-MS shows its efficiency for (1) the study of PRP–tannin interactions, (2) the determination of stoichiometry, and (3) the study of complex stability. We were able to establish unambiguously both their stoichiometries and their overall subunit architecture via tandem mass spectrometry and solution disruption experiments. Our results prove that IB5·EgCG complexes are maintained intact in the gas phase. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: Oral astringency is the dry sensation experienced in the mouth on consumption of plant-based polyphenols (catechins) found in wine and tea as well as certain fruits and vegetables. It is commonly explained as arising from the loss of lubricity owing to the precipitation of proteins from the salivary film that coats and lubricates the oral cavity. Here, we investigate this hypothesis directly by probing the impact of astringent compounds on the lubricating properties of saliva. By preadsorbing saliva onto an elastic hydrophobic substrate to form a highly lubricating and robust film under conditions designed to mimic the low pressure rubbing contacts experienced in the oral cavity (Bongaerts, Rossetti, & Stokes, 2007), we probe the interaction of this film on exposure to solutions containing tea catechins. We examine the response of the adsorbed salivary film to polyphenol structure, concentration and temperature, as well as the influence of astringency modulating solutions consisting of a thickener (maltodextrin) and milk. We find that a significant increase in friction coefficient occurs upon exposure with epigallocatechin gallate (EGCG) solutions due to a depletion of the lubricating proteins from the elastic substrates. The friction coefficient increases more rapidly with increasing EGCG concentration, this is in line with a corresponding increase in astringency perception. In addition, the inclusion of a hydrocolloid thickener in EGCG solutions caused a decrease in astringency perception probably due to specific EGCG–maltodextrin interaction and to an increase in viscosity, which lowers the friction coefficient between the elastic substrates. These findings show that the physical interaction of saliva proteins with EGCG molecules, which we probe through the loss of saliva lubricity, can be advantageously used to predict the astringent acuity of EGCG using our simple oral mimetic technique, supporting the hypothesis that astringency is related to a loss of lubrication. However, epicatechin (EC) did not alter the lubricating properties of the salivary film, although the EC solutions were perceived to be astringent, an observation which seems to question a simple causal dependence on oral lubrication. In addition to that, milk mitigated the astringency perception of EGCG solutions although considerably reducing saliva lubricity. We conclude that the depletion of saliva lubricating proteins is not necessary to obtain an astringent perception, and that astringency is unlikely to be a purely tactile percept. [Copyright &y& Elsevier]

Astringency is one of the most complex oral sensations. This dry, puckering mouthfeel occurs when consuming wine, tea, or other foods containing polyphenols. The exact mechanism behind this dry mouthfeel is not completely understood. Here, we describe a systematic tribological approach to measure model and real saliva to understand the specific role of the salivary proteins (mucins and proline-rich proteins (PRPs)) on lubrication-based astringency. Our approach reveals that there are two routes towards lubrication losses, partly involving irreversible molecular mechanisms for which the order of reactivity matters. For human saliva, we find two lubrication mechanisms: (I) Using phenolic compounds, we find aggregation-induced lubrication losses due to hydrogen bond formation, which depend critically on phenol size: large polyphenols allow for aggregation-induced lubrication losses, but small phenols do not. (II) For metal salts combined with saliva, we observe aggregation without lubrication losses as a result of electrostatic interactions. We find that lubrication losses are caused by the specific removal of the salivary PRP layer, whereas mucin aggregation in the presence of PRPs does not lead to lubrication losses. Additionally, we show that the addition of solvents that are able to reduce protein-polyphenol hydrogen bonding (e.g. ethanol) can prevent lubrication losses. Lubrication losses can also be compensated by the addition of highly viscous fluids (glycerol) that can provide viscous lubrication. [Display omitted] • Large polyphenols aggregate PRPs leading to salivary lubrication losses related to astringency perception. • Mucin aggregation does not cause salivary lubrication losses when PRPs remain unaffected. • Salivary lubrication losses can be prevented by the addition of hydrogen-bond donors or highly viscous fluids. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism by which solutions containing polyphenols are perceived as astringent is not clearly understood. Salivary proline-rich proteins and histatins are products of salivary glands and rapidly bind polyphenols — thought to be the main astringent compound in such as tea and wine. However it is unclear how this interaction leads to the altered oral mouthfeel known as astringency which is characterised by a dry, puckered feeling all around the mouth. To determine the role of saliva in the perception of astringency a protocol was used to decrease the volume of saliva from the mouth (by washing with water) and then by chewing to increase the volume of saliva above resting levels. Following each of these conditions subjects tasted the same solution of black tea and were asked to rate the relative astringency. Compared to the astringency rating of black tea at rest the majority of subjects (10 out of 15) perceived an increase in astringency following washing the mouth with water. Most subjects then perceived a decrease in astringency following chewing compared to the previous state. In all subjects a reduction in salivary proteins was detected following water washout and an increase above resting levels detected following chewing although there was no change in oral mucosal wetness. A separate experiment revealed several of the proteins interacting following the water washout were salivary in origin. We conclude that salivary proteins in solution inhibit the mouthfeeling of astringency which is mediated, at least in part, by salivary proteins adhered to buccal mucosal cells. [Copyright &y& Elsevier]

Astringency plays an important role in the sensory experience of many foods and beverages, ranging from wine to nuts. Given the recent trend toward fortifying consumables with astringent compounds and the evidence regarding the health benefits of some astringents, the mechanisms and perceptual characteristics of astringency warrant further discussion and investigation. This paper reviews the current state of the literature, including consideration of new methods for describing and measuring astringency, and provides an overview of research concerned with elucidating the physical, physiological, and psychological factors that underlie and mediate perception of this sensation. [ABSTRACT FROM AUTHOR]

Abstract: Human whole saliva (HWS) is a complex physiological secretion that performs a number of essential functions such as protection of oral health, lubrication of mouth tissues, as well as predigestion of food. In addition, saliva forms the perireceptor environment of the oral cavity and, by its interactions with food and beverages, influences the transduction of aroma, taste and tactile (mouthfeel) perceptions. We investigate and report the impact of addition of compounds commonly found in oral health and beverage products (sodium dodecyl sulphate (SDS), citric acid and tea polyphenols: epigallocatechin gallate (EGCG), epicatechin (EC), rutin) on the interfacial shear elasticity of HWS obtained from a single subject. The aim of this work is to probe the relationship between surface shear elasticity of saliva and the astringent (puckering-like) mouthfeel arising from the consumption of products containing the investigated ingredients. Saliva proteins are extremely surface active and adsorb to the air–liquid interface to form a high-elastic “solid-like” surface film. Our findings show that the interfacial shear elasticity G′ of saliva is significantly reduced when mixed with citric acid, SDS or a tea polyphenol containing a galloyl ring in the molecule (EGCG). These results support the hypothesis that astringency arises from aggregation of salivary proteins, thereby reducing lubrication of oral tissues. Minor or no effect is observed from the interaction of saliva with EC or rutin. Furthermore, we investigate the possibility of using mucins as a simple model for saliva. Two selected mucins, tested at different concentrations and ionic strength, failed to mimic the elastic interfacial behaviour shown by saliva. [Copyright &y& Elsevier]

A rapidly growing area of whey protein use is in beverages. There are 2 types of whey protein-containing beverages: those at neutral pH and those at low pH. Astringency is very pronounced at low pH. Astringency is thought to be caused by compounds in foods that bind with and precipitate salivary proteins; however, the mechanism of astringency of whey proteins is not understood. The effect of viscosity and pH on the astringency of a model beverage containing whey protein isolate was investigated. Trained sensory panelists (n = 8) evaluated the viscosity and pH effects on astringency and basic tastes of whey protein beverages containing 6% wt/vol protein. Unlike what has been shown for alum and polyphenols, increasing viscosity (1.6 to 7.7 mPa⋅s) did not decrease the perception of astringency. In contrast, the pH of the whey protein solution had a major effect on astringency. A pH 6.8 whey protein beverage had a maximum astringency intensity of 1.2 (15-point scale), whereas that of a pH 3.4 beverage was 8.8 (15-point scale). Astringency decreased between pH 3.4 and 2.6, coinciding with an increase in sourness. Decreases in astringency corresponded to decreases in protein aggregation as observed by turbidity. We propose that astringency is related to interactions between positively charged whey proteins and negatively charged saliva proteins. As the pH decreased between 3.4 and 2.6, the negative charge on the saliva proteins decreased, causing the interactions with whey proteins to decrease. [ABSTRACT FROM AUTHOR]

Abstract: A feeling of mouth dryness occurs from actual drying of the oral surfaces or from sampling astringent substances such as polyphenols (e.g., tannins in brewed tea and wine), which bind proline-rich proteins in saliva to reduce its lubricity. Here we investigated the interactions between physical drying and the effect of polyphenols on the subjective state of oral hydration. Twelve subjects rated the perceived wetness/dryness of their mouth using a labeled magnitude scale, after the mouth was dried with air for 35 s, or the subjects waited for an equal period of time during which the mouth was not dried. Subsequently, 1.5 mL volumes of an astringent solution (5 g L−1 tannic acid in distilled water), distilled drinking water, or a sweet solution (40 g L−1 sugar in mango tea with no tannins) were introduced into the mouth. After swishing and swallowing, the subject rated the wetness of the mouth for 4.3 min. The liquids were found to differ in their ability to wet the mouth (p <0.0001). The least wet sensations were reported for the astringent solution, on average; however, the differences among liquids were not equally pronounced at all times during the observation period (p <0.02). When the mouth was normally hydrated (i.e., had not been dried), the wetting effectiveness of the three liquids, based on the ratings, differed most greatly immediately after they had been received and swallowed. In contrast, when the mouth was dried, the liquids did not differ at this time. That the astringent solution did not have less wetting effectiveness in the dried mouth was attributed to the absence of precipitable salivary proteins. The findings suggest that the refreshment value of astringent drinks, based on their perceived wetting effectiveness, may vary with the state of oral hydration. [Copyright &y& Elsevier]

Abstract: In the following work, subject saliva characteristics affecting panel astringency evaluation in phenolic mixtures were studied. Sixty subjects were selected on the basis of their salivary flow, haze developing capacity and protein concentration. Subjects rated the perceived astringency of tannic acid (TA), commercial procyanidin (PA) and grape seed extract (GSE) solutions with concentration values ranging from 0.42 to 1.4g/L. Astringency intensity perception proved to be inversely related to saliva flow rate and haze developing capacity. No significant correlations were found between saliva protein concentration and intensity of astringency perception. A panel selected on the basis of subject similarity for flow rate and haze developing capacity rated the astringency intensity of set sample training solutions of TA, PA and GSE with concentrations ranging from 0.39 to 4.48g/L. The reactivity of the same astringent solutions with mucin was measured in an in vitro assay and expressed in terms of Nephelometric Turbidity Units (NTU). Three predictive models described by a linear regression of astringency intensity vs. NTU were found. The possibility of a practical application of the proposed assay for optimization of wine production was evaluated on 18 experimental wines. A linear correlation was found between the intensity astringency ratings of wine samples and the in vitro assay response. [Copyright &y& Elsevier]