Influence of the glycosylation of human salivary proline-rich proteins on their interactions with condensed tannins

Astringency sensitivity to tannic acid: Effect of ageing and salivary proline-rich protein levels

The link between salivary composition and sensitivity to astringency as a function of age has still not been established. In this work, we propose the hypothesis that ageing leads to changes in the concentration of salivary proline-rich proteins (PRPs), which alters the astringency perception threshold with age. To test this hypothesis, astringency sensitivity to tannic acid and saliva was assessed in 30 elderly people and 24 young people. Basic PRPs (bPRPs) and glycosylated PRPs (gPRPs) were quantified immunochemically via western blot analysis. The results showed that the amounts of bPRPs and gPRPs were similar between the young and elderly groups. However, a positive correlation between the gPRP amount and astringency threshold was observed only in the young group, while a negative correlation between the bPRP amount and astringency threshold was observed only in the elderly group. This finding suggests differences in the contribution of PRP type to astringency perception as a function of age.

Condensed tannins-Their content in plant foods, changes during processing, antioxidant and biological activities

Condensed tannins are considered nutritionally undesirable, because they precipitate proteins, inhibit digestive enzymes, and can affect the absorption of vitamins and minerals. From the consumer's point of view, they impart astringency to foods. Yet, they are viewed as a double-edged sword, since they possess antioxidant and anti-inflammatory activities. Intake of a small quantity of the right kind of tannins may in fact be beneficial to human health. This chapter reports on the chemical structure of condensed tannins, their content in plants and food of plant origin, how they are extracted, and methods for their determination. A description of the effects of processing on condensed tannins is discussed and includes soaking, dehulling, thermal processing (i.e., cooking, boiling, autoclaving, extrusion), and germination. The astringency of condensed tannins is described in relation to their interactions with proteins. Finally, details about the biological properties of condensed tannins, including their antimicrobial, anti-inflammatory, anticancer, anti-diabetic, and anti-obesity activities, are reviewed.

Different physicochemical interactions between varietal wines and human saliva: Correspondence with astringency

Astringency corresponds to the sensation of dryness and roughness that is experienced in the oral cavity in association with the interaction between salivary proteins and food polyphenols. In this study, the phenolic composition of seven varietal wines, the intensity of astringency they evoke and the physicochemical reactivity of these wines with whole human saliva were evaluated. Phenolic composition of wines was characterized by spectrophotometry and HPLC chromatography. Intensity of astringency was evaluated by trained sensory panels. Saliva from a single volunteer subject was used to assess wine-saliva interactions. To this end, binary mixtures were produced at different v/v wine/saliva ratios and each of them assayed for the ability of the salivary protein to diffuse on a cellulose membrane (diffusion test) and to remain in solution (precipitation test). Physicochemical reactivities between wine components and the protein fraction of saliva were contrasted against the astringency and the phenolic profile of each varietal wine. The study supports the view that astringency depends on physicochemical interactions between two complex matrices -wine and saliva- and not between some of their particular components.

Paper chromatography approach for the assessment of interaction between red wine and whole saliva

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.

Interactions between Salivary Proteins and Dietary Polyphenols: Potential Consequences on Gastrointestinal Digestive Events

The present review documents the current knowledge and hypotheses on how polyphenols-saliva interactions may modulate the bioaccessibility or bioavailability of nutrients and highlights research prospects in the field. After an updated description of the different classes of dietary polyphenols and their modifications by food processing or digestion, an overview of interactions between salivary proteins and polyphenols (with an emphasis on tannins) is provided. In vitro studies show that the solubility of salivary protein-tannin complexes in gastric conditions depends on the degree of tannin polymerization, while complexes are partly solubilized by bile salts. Salivary proteins-polyphenols interactions may affect digestive processes. For example, polyphenols can bind to and inhibit salivary amylase, with downstream consequences on starch digestion. Some salivary proteins (PRPs) prevent tannin-induced reduced protein digestibility, probably through binding tannins before they interact with digestive proteases. Salivary proteins may also act as scavenger molecules to limit the intestinal uptake of tannins.

A secret of salivary secretions: Multimodal effect of saliva in sensory perception of food

Saliva plays multifunctional roles in oral cavity. Even though its importance for the maintenance of oral health has long been established, the role of saliva in food perception has attracted increasing attention in recent years. We encourage researchers to discover the peculiarity of this biological fluid and aim to combine the data concerning all aspects of the saliva influence on the sensory perception of food. This review presents saliva as a unique material, which modulates food perception due to constant presence of saliva in the mouth and thanks to its composition. Therefore, we highlight the salivary components that contribute to these effects. Moreover, this review is an attempt to structure the effects of saliva on perception of different food categories, where the mechanisms of salivary impact in perception of liquid, semi-solid, and solid foods are revealed. Finally, we emphasize that the large inter-individual variability in salivary composition and secretion appear to contribute to the fact that everyone experiences food in their own way. Therefore, the design of the sensory studies should consider the properties of volunteers' saliva and also carefully monitor the experimental conditions that affect salivary composition and flow rate.

An overview of the perception and mitigation of astringency associated with phenolic compounds

Astringency, as a kind of puckering, drying, or rough sensation, is widely perceived from natural foods, especially plants rich in phenolic compounds. Although the interaction and precipitation of salivary proteins by phenolic compounds was often believed as the major mechanism of astringency, a definitive theory about astringency is still lacking due to the complex oral sensations. The interaction with oral epithelial cells and the activation of trigeminal chemoreceptors and mechanoreceptors also shed light on some of the phenolic astringency mechanisms, which complement the insufficient mechanism of interaction with salivary proteins. Since phenolic compounds with different types and structures show different astringency thresholds in a certain regularity, there might be some relationships between the phenolic structures and perceived astringency. On the other hand, novel approaches to reducing the unfavorable perception of phenolic astringency have been increasingly emerging; however, the according summary is still sparse. Therefore, this review aims to: (a) illustrate the possible mechanisms of astringency elicited by phenolic compounds, (b) reveal the possible relationships between phenolic structures and perception of astringency, and (c) summarize the emerging mitigation approaches to astringency triggered by phenolic compounds. This comprehensive review would be of great value to both the understanding of phenolic astringency and the finding of appropriate mitigation approaches to phenolic astringency in future research.

Tannins in Food: Insights into the Molecular Perception of Astringency and Bitter Taste

Astringency and bitterness are organoleptic properties widely linked to tannin compounds. Due to their significance to food chemistry, the food industry, and to human nutrition and health, these tannins' taste properties have been a line of worldwide research. In recent years, significant advances have been made in understanding the molecular perception of astringency pointing to the contribution of different oral key players. Regarding bitterness, several polyphenols have been identified has new agonists of these receptors. This review summarizes the last data about the knowledge of these taste properties perceived by tannins. Ultimately, tannins' astringency and bitterness are hand-in-hand taste properties, and future studies should be adapted to understand how the proper perception of one taste could affect the perception of the other one.

Natural Tannin Wood Extracts as a Potential Food Ingredient in the Food Industry

Wood extracts are one of the most important natural sources of industrially obtained tannins. Their use in the food industry could be one of the biggest (most important) recent innovations in food science as a result of their multiple (many) possible applications. The use of tannin wood extracts (TWEs) as additives directly added in foods or in their packaging meets an ever-increasing consumer demand for innovative approaches to sustainability. The latest research is focusing on new ways to include them directly in food, to take advantage of their specific actions to prevent individual pathological conditions. The present review begins with the biology of TWEs and then explores their chemistry, specific sensorial properties, and current application in food production. Moreover, this review is intended to cover recent studies dealing with the potential use of TWEs as a starting point for novel food ingredients.

Maillard-Reacted Whey Protein Isolates and Epigallocatechin Gallate Complex Enhance the Thermal Stability of the Pickering Emulsion Delivery of Curcumin

In this study, whey protein isolates (WPI), lactose (Lac) Maillard-reacted products, and epigallocatechin gallate (EGCG) complex were used to enhance the thermal stability of the Pickering emulsion delivery of curcumin. Atomic force microscopy combined with Fourier transform infrared spectroscopy were employed to study the morphological characteristics and structural changes of WPI-Lac/EGCG nanoparticles. Results proved that WPI-Lac and EGCG were combined by hydrogen bonding and hydrophobic interaction. The mechanism underlying WPI-Lac/EGCG-stabilized Pickering emulsion was further characterized by confocal laser scanning microscopy. The optimal binding ratio of WPI-Lac to EGCG was 1:1 (w/w) at pH 3.0. The particle size and zeta potential of the WPI-Lac/EGCG nanoparticles were about 110 nm and 27 mV, respectively. Analysis of microstructure and droplet size distribution revealed that the glycated WPI-Lac/EGCG-stabilized emulsions exhibited more uniform droplet distribution, stronger thermal stability, and higher curcumin percentage retention than WPI. These results indicate that the WPI-Lac/EGCG nanoparticles are potential stabilizers for Pickering emulsion requirements. This study provides a basis for the construction of Pickering emulsion systems while carrying pro-/hydrophobic bioactive components.

The Effects of Different Degrees of Procyanidin Polymerization on the Nutrient Absorption and Digestive Enzyme Activity in Mice

Proanthocyanidins, including polymers with both low and high degrees of polymerization, are the focus of intensive research worldwide due to their high antioxidant activity, medicinal applications, and pharmacological properties. However, the nutritional value of these compounds is limited because they readily form complexes with proteins, polysaccharides, and metal ions when consumed. In this study, we examined the effects of proanthocyanidins with different degrees of polymerization on white mice. Twenty-four male white mice were randomly divided into three groups of eight mice each and fed proanthocyanidins with a low degree of polymerization or a high degree of polymerization or a distilled water control via oral gavage over a 56-day period. We examined the effects of these proanthocyanidins on digestive enzyme activity and nutrient absorption. Compared to the control group, the group fed high-polymer proanthocyanidins exhibited a significant reduction in net body mass, total food intake, food utility rate, amylase activity, protease activity, and major nutrient digestibility (p < 0.05), while the group fed low-polymerization proanthocyanidins only exhibited significant reductions in total food intake, α-amylase activity, and apparent digestibility of calcium and zinc (p < 0.05). Therefore, proanthocyanidins with a high degree of polymerization had a greater effect on digestive enzyme activity and nutrient absorption than did those with a low degree of polymerization. This study lays the foundation for elucidating the relationship between procyanidin polymerization and nutrient uptake, with the aim of reducing or eliminating the antinutritional effects of polyphenols.

Maillard-Reacted Whey Protein Isolates Enhance Thermal Stability of Anthocyanins over a Wide pH Range

The poor thermal and acid stabilities of anthocyanins greatly limit their industrial applications as functional food ingredients. This work investigated the ability of the Maillard reaction products (MRPs) of whey protein isolates and glucose to enhance the thermal stability of anthocyanins over the pH range of 2.0-7.0. Anthocyanin dispersions were subjected to up to 120 min of thermal treatment at 80 °C. The improvement in the color stability and antioxidant capacity of the anthocyanin dispersions indicated that MRP remarkably inhibited anthocyanin degradation. Fluorescence spectroscopy results suggested that anthocyanins and MRPs form complexes through hydrophobic interactions. These complexes effectively attenuated anthocyanin degradation under heat treatment at pH 6.0. The particle sizes of MRPs alone or in complex with anthocyanins remained unchanged after heating. The novel protein delivery system proposed in this study expands the applications of anthocyanins as acid- and heat-stable functional food ingredients.

Interactions between wine phenolic compounds and human saliva in astringency perception

Astringency is a complex perceptual phenomenon involving several sensations that are perceived simultaneously. The mechanism leading to these sensations has been thoroughly and controversially discussed in the literature and it is still not well understood since there are many contributing factors. Although we are still far from elucidating the mechanisms whereby astringency develops, the interaction between phenolic compounds and proteins (from saliva, oral mucosa or cells) seems to be most important. This review summarizes the recent trends in the protein-phenol interaction, focusing on the effect of the structure of the phenolic compound on the interaction with salivary proteins and on methodologies based on these interactions to determine astringency.

Mechanisms of astringency: Structural alteration of the oral mucosal pellicle by dietary tannins and protective effect of bPRPs

The interaction of tannins with salivary proteins is involved in astringency. This paper focussed on saliva lining oral mucosae, the mucosal pellicle. Using a cell-based model, the impact of two dietary tannins (EgC and EgCG) on the mucosal pellicle structure and properties was investigated by microscopic techniques. The role of basic Proline-Rich-Proteins (bPRPs) in protecting the mucosal pellicle was also evaluated. At low (0.05 mM) tannin concentration, below the sensory detection threshold, the distribution of salivary mucins MUC5B on cells remained unaffected. At 0.5 and 1 mM, MUC5B-tannin aggregates were observed and their size increased with tannin concentration and with galloylation. In addition, 3 mM EgCG resulted in higher friction forces measured by AFM. In presence of bPRPs, the size distribution of aggregates was greatly modified and tended to resemble that of the "no tannin" condition, highlighting that bPRPs have a protective effect against the structural alteration induced by dietary tannins.

Reactivation of peroxidase activity in human saliva samples by polyphenols

OBJECTIVES

The enzyme lactoperoxidase (LPO), which is released into several body fluids like saliva, is an essential part to maintain the oral bacterial homeostasis by catalysing the oxidation of thiocyanate (SCN^-) to hypo-thiocyanite (^-OSCN). The formation of unreactive redox intermediates (like Compound II) leads to a decreased pseudo-halogenating enzyme activity, which is associated with a higher risk for oral infections. According to former studies with bovine LPO selected flavonoids were tested in respect to their potential to reactivate the enzymatic activity in a more physiological, human salivary system.

DESIGN

Saliva samples from healthy donors were collected and characterized by using several gel staining methods and immunoblotting. Afterwards kinetic measurements were performed by applying the TNB-assay to evaluate the pseudo-halogenating salivary peroxidase (SAPX) activity. The measurements were performed in the presence of excess H₂O₂ to simulate pro-inflammatory conditions. Moreover selected flavonoids or an ethanolic extract of Tormentillae rhizoma were applied to test their regenerating effect on the LPO-derived ^-OSCN production.

RESULTS

Despite the complex protein composition of the collected saliva samples, an SAPX-derived pseudo-halogenating activity could be identified. The ^-OSCN regenerating effects of the tested polyphenols were completely comparable to previous in vitro experiments with bovine LPO. Thus, we could show that phenolic substances are suitable to regenerate the peroxidase activity in human saliva samples after H₂O₂-induced inactivation.

CONCLUSION

The studies provide new insights into the effect of pharmaceutical relevant polyphenols on salivary peroxidase activity and thus, suggest this enzyme as a new target for the prevention and therapy of oral inflammatory diseases.

Salivary proline-rich protein may reduce tannin-iron chelation: a systematic narrative review

Background

Tannins are often cited for antinutritional effects, including chelation of non-heme iron. Despite this, studies exploring non-heme iron bioavailability inhibition with long-term consumption have reported mixed results. Salivary proline-rich proteins (PRPs) may mediate tannin-antinutritional effects on non-heme iron bioavailability.

Aim

To review evidence regarding biochemical binding mechanisms and affinity states between PRPs and tannins, as well as effects of PRPs on non-heme iron bioavailability with tannin consumption in vivo.

Methods

Narrative systematic review and meta-analysis. Common themes in biochemical modeling and affinity studies were collated for summary and synthesis; data were extracted from in vivo experiments for meta-analysis.

Results

Thirty-two studies were included in analysis. Common themes that positively influenced tannin-PRP binding included specificity of tannin-PRP binding, PRP and tannin stereochemistry. Hydrolyzable tannins have different affinities than condensed tannins when binding to PRPs. In vivo, hepatic iron stores and non-heme iron absorption are not significantly affected by tannin consumption (d = −0.64-1.84; −2.7-0.13 respectively), and PRP expression may increase non-heme iron bioavailability with tannin consumption.

Conclusions

In vitro modeling suggests that tannins favor PRP binding over iron chelation throughout digestion. Hydrolyzable tannins are not representative of tannin impact on non-heme iron bioavailability in food tannins because of their unique structural properties and PRP affinities. With tannin consumption, PRP production is increased, and may be an initial line of defense against tannin-non-heme iron chelation in vivo. More research is needed to compare competitive binding of tannin-PRP to tannin-non-heme iron complexes, and elucidate PRPs’ role in adaption to non-heme iron bioavailability in vivo.

Electronic supplementary material

The online version of this article (doi:10.1186/s12986-017-0197-z) contains supplementary material, which is available to authorized users.

Sensorial properties of red wine polyphenols: Astringency and bitterness

Polyphenols have been the subject of numerous research over the past years, being referred as the nutraceuticals of modern life. The healthy properties of these compounds have been associated to a natural chemoprevention of 21st century major diseases such as cancer and neurodegenerative diseases (e.g. Parkinson's and Alzheimer's). This association led to an increased consumption of foodstuffs rich in these compounds such as red wine. Related to the ingestion of polyphenols are the herein revised sensorial properties (astringency and bitterness) which are not still pleasant. This review intends to be an outline both at a sensory as a molecular level of the mechanisms underlying astringency and bitterness of polyphenols. Up-to-date knowledge of this matter is discussed in detail.

Effect of the addition of flavan-3-ols on the HPLC-DAD salivary-protein profile

The interaction between monomeric flavan-3-ols and salivary proteins has been studied using HPLC-DAD. A chromatographic method has been described and seven protein fractions were collected. The peptides and proteins present in each fraction have been identified using nLC-MS-MS analysis. The interaction between saliva and catechin, epicatechin and gallocatechin has been studied. These compounds interact in a discriminated way with salivary proteins: catechin causes a decrease of some fractions, epicatechin causes the decrease or increase of fractions while gallocatechin seems to cause an increase of two fractions. This variable behavior is explained, for the decrease in the chromatographic area, by the precipitation of salivary proteins and, for the increase of the area, by the formation of soluble complexes and/or for the formation of new peaks.

New Anthocyanin-Human Salivary Protein Complexes

The interaction between phenolic compounds and salivary proteins is considered the basis of the poorly understood phenomenon of astringency. Furthermore, this interaction is an important factor in relation to their bioavailability. In this work, interactions between anthocyanin and human salivary protein fraction were studied by mass spectrometry (MALDI-TOF-MS and FIA-ESI-MS) and saturation-transfer difference (STD) NMR spectroscopy. Anthocyanins were able to interact with saliva proteins. The dissociation constant (KD) between malvidin 3-glucoside and salivary proline-rich proteins was 1.92 mM for the hemiketal form (pH 3.4) and 1.83 mM for the flavylium cation (pH 1.0). New soluble complexes between these salivary proteins and malvidin 3-glucoside were identified for the first time.

Interactions of polyphenols with carbohydrates, lipids and proteins

Polyphenols are secondary metabolites in plants, investigated intensively because of their potential positive effects on human health. Their bioavailability and mechanism of positive effects have been studied, in vitro and in vivo. Lately, a high number of studies takes into account the interactions of polyphenols with compounds present in foods, like carbohydrates, proteins or lipids, because these food constituents can have significant effects on the activity of phenolic compounds. This paper reviews the interactions between phenolic compounds and lipids, carbohydrates and proteins and their impact on polyphenol activity.

In vivo interactions between procyanidins and human saliva proteins: effect of repeated exposures to procyanidins solution

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.

Understanding glycoprotein behaviours using Raman and Raman optical activity spectroscopies: characterising the entanglement induced conformational changes in oligosaccharide chains of mucin

We illustrate the great potential of Raman and ROA spectroscopies for investigating the structure and organisation of glycoproteins and the complex matrices they can form. In combination these spectroscopic techniques are sensitive to changes in conformation revealing details of secondary and tertiary structures, probing hydrogen bonding interactions, as well as resolving side chain orientation and the absolute configuration of chiral substructures. To demonstrate this potential we have characterised the structural changes in a complex glycoprotein, mucin. Spectral changes were observed during the entanglement transition as the mucin concentration was increased. By applying two-dimensional correlation analysis (2DCos) to the ROA and Raman concentration-dependent spectral sets delicate transitions in mucin conformation could also be determined. From ~20-40 mg/ml conformational transitions assigned mainly to the sugar N-acetyl-d-galactosamine (GalNAc), which is the linking saccharide unit to the protein backbone, were monitored. Further changes in local oligosaccharide conformation above 40 mg/ml were also monitored, together with other structural transitions observed in the protein core, particularly β-structure formation. Consequently, these spectral techniques were shown to monitor the formation of transient entanglements formed by brush-brush interactions between oligosaccharide combs of mucin molecules identifying changes in both carbohydrate and protein moieties. This work clearly shows how these methods can be used to elucidate fresh insights into the complex behaviour of these large complex molecules.

Carbohydrates inhibit salivary proteins precipitation by condensed tannins

Condensed tannins are a group of polyphenols that are associated with the astringency sensation, as they readily interact and precipitate salivary proteins. As this interaction is affected by carbohydrates, the aim of this work was to study the effect of some carbohydrates used in the food industry [arabic gum (AG), pectin, and poligalacturonic acid (PGA)] on the salivary proteins/grape seed procyanidins interaction. This was assessed monitoring the salivary proteins that remain soluble in the presence of condensed tannins with the addition of carbohydrates (HPLC) and analysis of the respective precipitates (SDS-PAGE). The results show that pectin was the most efficient in inhibiting protein/tannin precipitation, followed by AG and PGA. The results suggest that pectin and PGA exert their effect by formation of a ternary complex protein/polyphenol/carbohydrate, while AG competes with proteins for tannin binding (competition mechanism). The results also point out that both hydrophilic and hydrophobic interactions are important for the carbohydrate effects.

Induced and constitutive responses of digestive enzymes to plant toxins in an herbivorous mammal

Many plants produce plant secondary compounds (PSCs) that bind and inhibit the digestive enzymes of herbivores, thus limiting digestibility for the herbivore. Herbivorous insects employ several physiological responses to overcome the anti-nutritive effects of PSCs. However, studies in vertebrates have not shown such responses, perhaps stemming from the fact that previously studied vertebrates were not herbivorous. The responses of the digestive system to dietary PSCs in populations of Bryant's woodrat (Neotoma bryanti) that vary in their ecological and evolutionary experience with the PSCs in creosote bush (Larrea tridentata) were compared. Individuals from naïve and experienced populations were fed diets with and without added creosote resin. Animals fed diets with creosote resin had higher activities of pancreatic amylase, as well as luminal amylase and chymotrypsin, regardless of prior experience with creosote. The experienced population showed constitutively higher activities of intestinal maltase and sucrase. Additionally, the naïve population produced an aminopeptidase-N enzyme that was less inhibited by creosote resin when feeding on the creosote resin diet, whereas the experienced population constitutively expressed this form of aminopeptidase-N. Thus, the digestive system of an herbivorous vertebrate responds significantly to dietary PSCs, which may be important for allowing herbivorous vertebrates to feed on PSC-rich diets.

Aversive effect of tannic acid on drinking behavior in mice of an inbred strain: potential animal model for assessing astringency

Astringency, an orosensory sensation associated with dietary tannins, contributes to food appetitiveness/aversiveness. However, astringency perception varies greatly among individuals. This study examined whether genetically homogeneous naïve mice display appetitiveness/aversiveness when provided with tannin-containing drink solutions. Ingestion of serial dilutions of tannic acid (TA) by inbred mice (A/Snell) was assessed by a one-bottle preference test. Drink intake was far predominant at night (circadian rhythm). TA concentration-dependently inhibited daily drink consumption. Overnight consumption of TA solutions (range = 0.5-8 g/L) decreased linearly to zero during the first night and was recovered significantly during subsequent nights. TA also inhibited drink consumption in another two inbred mouse strains. The protein fraction of saliva collected from naive mice was markedly reactive with TA at the concentrations shown to affect drink consumption. Thus, testing for drink ingestion in inbred mice during short-term (overnight) exposure to tannin-containing liquid foods represents an advantageous animal model for assessing astringency.

Quantitative colorimetric assay for total protein applied to the red wine Pinot noir

A standard method for assaying protein in red wine is currently lacking. The method described here is based on protein precipitation followed by dye binding quantification. Improvements over existing approaches include minimal sample processing prior to protein precipitation with cold trichloroacetic acid/acetone and quantification based on absorbance relative to a commercially available standard representative of proteins likely to be found in wine, the yeast mannoprotein invertase. The precipitation method shortened preparation time relative to currently published methods and the mannoprotein standard yielded values comparable to those obtained by micro-Kjeldahl analysis. The assay was used to measure protein in 48 Pinot noir wines from 6 to 32 years old. The protein content of these wines was found to range from 50 to 102 mg/L with a mean value of 70 mg/L. The availability of a simple and relatively rapid procedure for assaying protein provides a practical tool to quantify a wine component that has been overlooked in routine analyses of red wines.

Reactivity of human salivary proteins families toward food polyphenols

Tannins are well-known food polyphenols that interact with proteins, namely, salivary proteins. This interaction is an important factor in relation to their bioavailability and is considered the basis of several important properties of tannins, namely, the development of astringency. It has been generally accepted that astringency is due to the tannin-induced complexation and/or precipitation of salivary proline-rich proteins (PRPs) in the oral cavity. However, this complexation is thought to provide protection against dietary tannins. Neverthless, there is no concrete evidence and agreement about which PRP families (acidic, basic, and glycosylated) are responsible for the interaction with condensed tannins. In the present work, human saliva was isolated, and the proteins existing in saliva were characterized by chromatographic and proteomic approaches (HPLC-DAD, ESI-MS, sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), and MALDI-TOF). These approaches were also adapted to study the affinity of the different families of salivary proteins to condensed tannins by the interaction of saliva with grape seed procyanidins. The results obtained when all the main families of salivary proteins are present in a competitive assay, like in the oral cavity, demonstrate that condensed tannins interact first with acidic PRPs and statherin and thereafter with histatins, glycosylated PRPs, and bPRPs.

The effect of tannins on Mediterranean ruminant ingestive behavior: the role of the oral cavity

Sheep, cattle and goat are domestic ruminants of significant economic interest in the Mediterranean region. Although sharing the same pasture ranges, they ingest different plants and plant parts and, consequently different levels of tannins. This suggests an ability to detect and adapt ingestion according to animal physiological limits of tolerance for plant secondary metabolites. This review will detail the effects of dietary tannins on feeding behavior, and the role of the oral cavity in this process, with focus on such ruminant species. The role of salivary protein profile in tannin perception in the oral cavity, and as a defense mechanism, will be discussed.

Capillary electrophoresis methods for the determination of covalent polyphenol-protein complexes

The bioactivities and bioavailability of plant polyphenols including proanthocyanidins and other catechin derivatives may be affected by covalent reaction between polyphenol and proteins. Both processing conditions and gastrointestinal conditions may promote formation of covalent complexes for polyphenol-rich foods and beverages such as wine. Little is known about covalent reactions between proteins and tannin, because suitable methods for quantitating covalent complexes have not been developed. We established capillary electrophoresis methods that can be used to distinguish free protein from covalently bound protein-polyphenol complexes and to monitor polyphenol oxidation products. The methods are developed using the model protein bovine serum albumin and the representative polyphenol (-)epigallocatechin gallate. By pairing capillaries with different diameters with appropriate alkaline borate buffers, we are able to optimize resolution of either the protein-polyphenol complexes or the polyphenol oxidation products. This analytical method, coupled with purification of the covalent complexes by diethylaminoethyl cellulose chromatography, should facilitate characterization of covalent complexes in polyphenol-rich foods and beverages such as wine.

Wine and grape tannin interactions with salivary proteins and their impact on astringency: a review of current research

Astringency is an important characteristic of red wine quality. The sensation is generally thought to be produced by the interaction of wine tannins with salivary proteins and the subsequent aggregation and precipitation of protein-tannin complexes. The importance of wine astringency for marketability has led to a wealth of research on the causes of astringency and how tannins impact the quality of the sensation, particularly with respect to tannin structure. Ultimately, the understanding of how tannin structure impacts astringency will allow the controlled manipulation of tannins via such methods as micro-oxygenation or fining to improve the quality of wines.

Proline-rich salivary proteins have extended conformations

Three basic proline-rich salivary proteins have been produced through the recombinant route. IB5 is a small basic proline-rich protein that is involved in the binding of plant tannins in the oral cavity. II-1 is a larger protein with a closely related backbone; it is glycosylated, and it is also able to bind plant tannins. II-1 ng has the same polypeptidic backbone as II-1, but it is not glycosylated. Small angle x-ray scattering experiments on dilute solutions of these proteins confirm that they are intrinsically disordered. IB5 and II-1 ng can be described through a chain model including a persistence length and cross section. The measured radii of gyration (Rg=27.9 and 41.0+/-1 A respectively) and largest distances (rmax=110 and 155+/-10 A respectively) show that their average conformations are rather extended. The length of the statistical segment (twice the persistence length) is b=30 A, which is larger than the usual value (18 A-20 A) for unstructured polypeptide chains. These characteristics are presumably related to the presence of polyproline helices within the polypeptidic backbones. For both proteins, the radius of gyration of the chain cross-section is Rc=2.7+/-0.2A. The glycosylated protein II-1 has similar conformations but the presence of large polyoside sidegroups yields the structure of a branched macromolecule with the same hydrophobic backbone and hydrophilic branches. It is proposed that the unusually extended conformations of these proteins in solution facilitate the capture of plant tannins in the oral cavity.

Ability of a salivary intrinsically unstructured protein to bind different tannin targets revealed by mass spectrometry

Astringency 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.

Systematic identification of yeast proteins extracted into model wine during aging on the yeast lees

Total protein and protein-associated mannan concentrations were measured, and individual proteins were identified during extraction into model wines over 9 months of aging on the yeast lees following completion of fermentations by seven wine strains of Saccharomyces cerevisiae. In aged wines, protein-associated mannan increased about 6-fold (+/-66%), while total protein only increased 2-fold (+/-20%), which resulted in a significantly greater protein-associated mannan/total protein ratio for three strains. A total of 219 proteins were identified among all wine samples taken over the entire time course. Of the 17 "long-lived" proteins detected in all 9 month samples, 13 were cell wall mannoproteins, and four were glycolytic enzymes. Most cytosolic proteins were not detected after 6 months. Native mannosylated yeast invertase was assayed for binding to wine tannin and was found to have a 10-fold lower affinity than nonglycosylated bovine serum albumin. Enrichment of mannoproteins in the aged model wines implies greater solution stability than other yeast proteins and the possibility that their contributions to wine quality may persist long after bottling.