Effect of malvidin-3-glucoside and epicatechin interaction on their ability to interact with salivary proline-rich proteins

A look upon the adsorption of different astringent agents to oral models: Understanding the contribution of alternative mechanisms in astringency

Salivary proteins precipitation by interaction with polyphenols is the major mechanism for astringency. However, alternative mechanisms seem involved in the perception of different subqualities of astringency. In this study, adsorption of four astringent agents to in vitro oral models and their sensory properties were assessed. Overall, green tea infusion and tannic acid have shown a higher adsorption potential for models with oral cells and absence of saliva. Alum and grape seed extract presented higher adsorption in models with presence of oral cells and saliva. Multiple factor analysis suggested that adsorption may represent important mechanisms to elicit the astringency of alum. Models including saliva, were closely associated with overall astringency and aggressive subquality. Models with cells and absent saliva were closely associated with greenness, suggesting a taste receptor mechanism involvement in the perception. For the first time a correlation between an oral-cell based assay and astringency sensory perception was shown.

Supramolecular Study of the Interactions between Malvidin-3-O-Glucoside and Wine Phenolic Compounds: Influence on Color

Supramolecular study of the interactions between the major wine anthocyanin, malvidin-3-O-glucoside (Mv3G) and different wine phenolic compounds (quercetin 3-O-β-glucopyranoside (QG), caffeic acid, (-)-epicatechin, (+)-catechin, and gallic acid) has been performed at two different molar ratios (1:1 and 1:2) in acidic medium where flavylium cation predominates (pH ≤ 2). Color variations have been evaluated by differential colorimetry using CIELAB color space. These studies have been complemented with isothermal titration calorimetry assays and molecular dynamics simulations. The color of Mv3G flavylium cation is modified by the interaction with QG toward more bluish and intense colors. Interaction constants between the anthocyanin and the different phenolic compounds were obtained, ranging from 9.72 × 108 M-1 for QG to 1.50 × 102 M-1 for catechin. Hydrophobic interactions and H-bonds are the main driving forces in the pigment/copigment aggregation, except for the interactions where caffeic acid is involved, in which hydrophobic interactions acquire greater preponderance.

Role of Anthocyanins in the Interaction between Salivary Mucins and Wine Astringent Compounds

Wine astringency is a very complex sensation whose complete mechanism has not been entirely described. Not only salivary proline-rich proteins (PRPs) are involved in its development; salivary mucins can also play an important role. On the other hand, it has been described that anthocyanins can interact with PRPs, but there is no information about their potential role on the interactions with mucins. In this work, the molecular interactions between salivary mucins (M) and different wine phenolic compounds, such as catechin (C), epicatechin (E) and quercetin 3-β-glucopyranoside (QG), as well as the effect of the anthocyanin malvidin 3-O-glucoside (Mv) on the interactions with mucins, were assessed by isothermal titration calorimetry (ITC). Results showed that the interaction between anthocyanin and mucins is stronger than that of both flavanols analyzed, since the affinity constant values were 10 times higher for anthocyanin than for catechin, the only flavanol showing interaction in binary assay. Moreover, at the concentration at which polyphenols are usually found in wine, flavonols seem not to be involved in the interactions with mucins. These results showed, for the first time, the importance of wine anthocyanins in the mechanisms of astringency involving high-molecular-weight salivary proteins like mucins.

The phenolic profile of walnut meal protein isolate and interaction of phenolics with walnut protein

The aim of this study was to interpret the interaction of phenolics with walnut protein and determine their effects on protein functional properties. The phenolic profiles of walnut meal (WM) and walnut meal protein isolate (WMPI) were established using UPLC-Q-TOF-MS. A total of 132 phenolic compounds were detected, including 104 phenolic acids and 28 flavonoids. Phenolic compounds bound to protein via hydrophobic interactions, hydrogen bonds, and ionic bonds were identified in WMPI. They were also present as free forms, but the hydrophobic interactions and hydrogen bonds were the main non-covalent binding forces between phenolics and walnut proteins. The interaction mechanisms were further supported by the fluorescence spectra of WMPI with ellagic acid and quercitrin. In addition, changes in the functional properties of WMPI after removal of phenolic compounds were evaluated. Dephenolization significantly increased water holding capacity, oil absorptive capacity, foaming capacity, foaming stability, emulsifying stability index, and the in vitro gastric digestibility. However, in vitro gastric-intestinal digestibility was not significantly affected. These results provide insights into the interactions between walnut protein and phenolics, which indicates potential strategies for removing phenolics from walnut protein.

Mouthfeel subqualities in wines: A current insight on sensory descriptors and physical-chemical markers

Astringency and more generally mouthfeel perception are relevant to the overall quality of the wine. However, their origin and description are still uncertain and are constantly updating. Additionally, the terminology related to mouthfeel properties is expansive and extremely diversified, characterized by common traditional terms as well as novel recently adopted descriptors. In this context, this review evaluated the mention frequency of astringent subqualities and other mouthfeel attributes in the scientific literature of the last decades (2000-August 17, 2022). One hundred and twenty-five scientific publications have been selected and classified based on wine typology, aim, and instrumental-sensorial methods adopted. Dry resulted as the most frequent astringent subquality (10% for red wines, 8.6% for white wines), while body-and related terms-is a common mouthfeel sensation for different wine types, although its concept is still vague. Alongside, promising analytical and instrumental techniques investigating and simulating the in-mouth properties are discussed in detail, such as rheology for the viscosity and tribology for the lubrication loss, as well as the different approaches for the quantitative and qualitative evaluation of the interaction between salivary proteins and astringency markers. A focus on the phenolic compounds involved in the tactile perception was conducted, with tannins being the compounds conventionally found responsible for astringency. Nevertheless, other non-tannic polyphenolic classes (i.e., flavonols, phenolic acids, anthocyanins, anthocyanin-derivative pigments) as well as chemical-physical factors and the wine matrix (i.e., polysaccharides, mannoproteins, ethanol, glycerol, and pH) can also contribute to the wine in-mouth sensory profile. An overview of mouthfeel perception, factors involved, and its vocabulary is useful for enologists and consumers.

Effect of the addition of soluble polysaccharides from red and white grape skins on the polyphenolic composition and sensory properties of Tempranillo red wines

Soluble polysaccharides from white (PSW) and red (PSR) grape skins were obtained to be evaluated as potential modulators of the unbalanced astringency of a Tempranillo red wine. The modulation of astringency was evaluated by a sensory panel and it seemed to be related to the changes in the polyphenolic profile. Isothermal Titration Calorimetry (ITC) studies, employed to characterize flavan-3-ol-polysaccharide interactions, showed that PSR decreased noticeably wine astringency causing a great flavan-3-ol loss (ca. 40 %), since they interacted more spontaneously with the flavan-3-ols (ca. ΔGtotal = -2.14 × 10⁴ cal/mol) than PSW (ca. ΔGtotal = -1.32 × 10⁴ cal/mol). The strength of these interactions seems to be related to the polysaccharide molecular size and to the presence of arabinogalactans in the structure. On the contrary, PSW showed no relevant effects on wine astringency. Furthermore, potential variations of color were also assessed and no deleterious effect was observed after the addition of any polysaccharide.

Wine astringency: more than just tannin-protein interactions

Red wines are characterized by their astringency, a very important sensory attribute that affects the perceived quality of wines. Three mechanisms have been proposed to explain astringency, and two theories describe how these mechanisms work in an integrated manner to produce tactile sensations such as drying, roughening, shrinking and puckering. The factors involved include not only tannins and salivary proteins, but also anthocyanins, grape polysaccharides and mannoproteins, as well as other wine matrix components that modulate their interactions. These multifactorial interactions could be responsible for different sensory responses and therefore need to be further studied. This review presents the latest advances in astringency perception and its possible origins, with special attention on the interactions of components, their impact on oral perception and the development of astringency sub-qualities. Future research efforts should concentrate on understanding the mechanisms involved as well as on the limiting factors related to the conformation and stability of the tannin-salivary protein complexes. © 2021 Society of Chemical Industry.

Natural and Synthetic Flavylium-Based Dyes: The Chemistry Behind the Color

Flavylium compounds are a well-known family of pigments because they are prevalent in the plant kingdom, contributing to colors over a wide range from shades of yellow-red to blue in fruits, flowers, leaves, and other plant parts. Flavylium compounds include a large variety of natural compound classes, namely, anthocyanins, 3-deoxyanthocyanidins, auronidins, and their respective aglycones as well as anthocyanin-derived pigments (e.g., pyranoanthocyanins, anthocyanin-flavan-3-ol dimers). During the past few decades, there has been increasing interest among chemists in synthesizing different flavylium compounds that mimic natural structures but with different substitution patterns that present a variety of spectroscopic characteristics in view of their applications in different industrial fields. This Review provides an overview of the chemistry of flavylium-based compounds, in particular, the synthetic and enzymatic approaches and mechanisms reported in the literature for obtaining different classes of pigments, their physical-chemical properties in relation to their pH-dependent equilibria network, and their chemical and enzymatic degradation. The development of flavylium-based systems is also described throughout this Review for emergent applications to explore some of the physical-chemical properties of the multistate of species generated by these compounds.

Evaluation of Blood-Brain Barrier Permeability of Polyphenols, Anthocyanins, and Their Metabolites

Anthocyanins (ACs) are able to protect neurons against β-amyloid-induced neurotoxicity. In this study, we evaluated blood-brain barrier (BBB) permeability of these compounds using a model kit to clarify the mechanism of AC on the brain. Black currant or strawberry AC extract was orally administrated to male Wistar rats. The urine and extirpated brain were collected before and after administration and analyzed quantitatively by liquid chromatography-tandem mass spectrometry. After administration of AC, several phenolic acids were detected in the urine samples. Further, AC and some AC metabolites were found in the brain tissue. BBB permeabilities of these compounds were much lower than the positive control. Epigallocatechin, daidzein, genistein, equol, and nobiletin presented high BBB permeability, whereas apigenin, luteolin, quercetin, and kaempferol showed medium permeability, and epicatechin, rutin, fisetin, resveratrol, and curcumin BBB permeation was neglected. These results suggested that ACs were difficult to cross BBB into the brain and ACs were not directly associated with the prevention of β-amyloid-induced neurotoxicity.

Understanding the molecular interactions between a yeast protein extract and phenolic compounds

Phenolic compounds are partially removed during fining, which may influence the organoleptic properties of beverages. Among phenolic compounds, tannins have been widely associated to the taste of beverages (namely astringency and bitterness). Furthermore, phenolic acids and anthocyanins may also influence bitterness and the latter are also responsible for beverages' color. Thus, it is necessary to perform molecular studies to better understand the effect of fining agents in the overall phenolic composition of beverages and the resulting organoleptic changes. The molecular interactions between these three classes of phenolic compounds and a yeast protein extract (YPE), designed as a new fining agent, was studied. The binding affinities were assessed by fluorescence quenching at two temperatures (21 °C and 37 °C) and in two reaction media (water and wine model solution). The size of aggregates formed was characterized by Dynamic Light Scattering and the selectivity of protein interaction was analyzed by electrophoresis. Overall, pentagalloylglucoside (tannin) showed the highest binding affinity for YPE, followed by malvidin 3-glucoside (anthocyanin), p-coumaric acid (phenolic acid) and gallic acid (phenolic acid). The studied temperatures and solvents affected the interaction affinities as well as the aggregates' size. Binding selectivity of proteins from YPE was not found. These results open new perspectives to control the fining process by using the YPE as a fining agent taking into account the further effect in the organoleptic properties of beverages.

Addition of chocolate milk to diet corresponds to protein concentration changes in human saliva

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.

Time Course of Salivary Protein Responses to Cranberry-Derived Polyphenol Exposure as a Function of PROP Taster Status

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.

Impact of B-Ring Substitution and Acylation with Hydroxy Cinnamic Acids on the Inhibition of Porcine α-Amylase by Anthocyanin-3-Glycosides

An inhibitory effect on α-amylase and α-glucosidase is postulated for polyphenols. Thus, ingestion of those secondary plant metabolites might reduce postprandial blood glucose level (hyperglycemia), which is a major risk factor for diabetes mellitus type II. In addition to a previous study investigating structure-effect relationships of different phenolic structures, the effect of anthocyanins is studied in detail here, by applying an α-amylase activity assay, on the basis of the conversion of 2-chloro-4-nitrophenyl-4-O-ß-galactopyranosyl maltoside (GalG₂CNP) and detection of CNP release by UV/Vis spectroscopy and isothermal titration calorimetry (ITC). All anthocyanin-3-glucosides showed a mixed inhibition with a strong competitive proportion, K_ic < 134 µM and K_iu < 270 µM; however, the impact of the B-ring substitution was not statistically significant. UV/Vis detection failed to examine the inhibitory effect of acylated cyanidins isolated from black carrot (Daucus carota ssp. Sativus var. Autrorubens Alef.). However, ITC measurements reveal a much stronger inhibitory effect compared to the cyanidin-3-glucoside. Our results support the hypothesis that anthocyanins are efficient α-amylase inhibitors and an additional acylation with a cinnamic acid boosts the observed effect. Therefore, an increased consumption of vegetables containing acylated anthocyanin derivatives might help to prevent hyperglycemia.

Interaction of Structurally Diverse Phenolic Compounds with Porcine Pancreatic α-Amylase

A blood glucose level lowering effect is postulated for polyphenols (PPs), which is in part attributed to the inhibition of α-amylase. To estimate structure-effect relationships, chlorogenic acid (CA), phlorizin (PHL), epigallocatechin gallate (EGCG), epicatechin (EC), and malvidin-3-glucoside (Mlv-3-glc) were used as inhibitors in an enzyme assay, on the basis of the conversion of GalG₂CNP by α-amylase. The detection of CNP was performed by UV/vis spectroscopy. The data reveal that the inhibitor strength decreases as follows: EGCG > Mlv-3-glc > EC > PHL ∼ CA. Detection of the substrate conversion by isothermal titration calorimetry supports these results. All PPs showed mixed inhibition, except for CA and EGCG wherein the competitive proportion was predominant. Investigations by saturation transfer difference NMR revealed interaction of PPs with α-amylase prevalently based on interactions with the aromatic or conjugated system. A correlation between the extent of the conjugated system and the IC₅₀ of the PP could be found.

Impact of polyphenols on receptor-ligand interactions by NMR: the case of neurotensin (NT)-neurotensin receptor fragment (NTS1) complex

Ligand-receptor interactions can be implicated in many pathological events such as chronic neurodegenerative diseases. Thus, the discovery of molecules disrupting this type of interactions could be an interesting therapeutic approach. Polyphenols are well known for their affinity for proteins and several studies have characterized these direct interactions. But studying the direct influence of multi-therapeutic drugs on a ligand-receptor complex relevant to a neurodegenerative disorder is a challenging issue. Solution NMR, molecular modeling and iterative calculations were used to obtain information about the interaction between a phenolic compound, α-glucogallin (α-2) and a ligand/fragment receptor complex neurotensin (NT) and its receptor NTS1. The α-2 was shown to bind to NT and a peptidic fragment of its NTS1 receptor, independently. Although the formation of the corresponding ligand-receptor complex did not seem to be affected, this experimental modeling protocol will enable the evaluation of other anti-amyloidogenic compounds such as blockers of NT-NTS1 binding. These types of studies help in understanding the specificity and influence in binding and can provide information to develop new molecules with a putative pharmacological interest.Communicated by Ramaswamy H. Sarma.

Chemical and sensorial investigation of in-mouth sensory properties of grape anthocyanins

Anthocyanins are water-soluble pigments found in the cell vacuoles of fruits and flowers, performing several roles from insects attraction to stress protection. Their antioxidant activity contributes to human health, and consuming plant-derived products provides their higher source in the diet. Although their colour and nutritional features, their contribution to sensory properties of foods has not been widely investigated. In wine, preferences are connected with sensory attributes of colour, aroma, taste, and mouthfeel. In this study, grape anthocyanin extracts (TAE) were fractionated using centrifugal partition chromatography (CPC) and preparative HPLC in three fractions, i.e glucoside (GF), acetylated (AF) and cinnamoylated (CF) anthocyanins. Sensory properties were investigated by chemical analysis, as reactivity towards bovin serum albumin (BSA) and salivary proteins, and in tasting sessions to assess anthocyanins best estimated thresholds (BET) in wine-like solution. Anthocyanins reacted with both BSA and salivary proteins, but to different extents, because higher interaction between salivary proteins and anthocyanins were found. Cinnamoylated anthocyanins are the most reactive to salivary proteins. Tasting sessions suggested an involvement of anthocyanins as in-mouth contributors in wine, since their BETs were 255, 297, 68, and 58 mg/L for TAE, GF, AF, and CF, respectively, and the descriptors reported were astringency and bitterness.