Exploring mouthfeel in model wines: Sensory-to-instrumental approaches

Astringency and its sub-qualities: a review of astringency mechanisms and methods for measuring saliva lubrication

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.

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.

Lubrication behavior of ex-vivo salivary pellicle influenced by tannins, gallic acid and mannoproteins

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.

Chemical Analysis of Commercial White Wines and Its Relationship with Consumer Acceptability

White wine consists of numerous chemical constituents such as volatile and nonvolatile compounds including organic acids and polyphenols, which can affect aroma and flavor profiles. In addition to the enological factors, chemical analysis of commercial wines is also important for understanding consumer perception. Volatile compounds are major contributors to wine aroma. Nonvolatile compounds affect the flavor of wine, through acidity, sweetness, bitterness, and astringency. The volatile aroma profiles of 12 commercial white wines were analyzed using headspace solid-phase microextraction (HS-SPME), with gas chromatography–mass spectrometry (GC–MS). High-performance liquid chromatography (HPLC) and a Y15 automatic analyzer were used to identify and quantify 10 polyphenols and 12 other target nonvolatile compounds. Sensory evaluation of sample wines was conducted by wine consumers. White wines were distinguished based on volatile and nonvolatile compositions. A total of 33 volatile compounds and 23 nonvolatile compounds were analyzed. Seven volatile compounds were correlated with consumer acceptability. Sugars are positively correlated with consumer preference, while nonvolatile substances such as acetic acid and catechins are negatively correlated with consumer preference. These results might further our understanding of the relationship between the chemical composition and consumer preferences in commercial wines.

Correlating wine astringency with physical measures - Current knowledge and future directions

Oral tribology receives growing attention in the field of food sciences as it offers great opportunities to establish correlations between physical parameters, such as the coefficient of friction, and sensory effects when interacting with components of the human mouth. One important aspect covers the astringency produced by wine, which can be described as the sensation of dryness and puckering in the mouth, specifically occurring between the tongue and the palate after swallowing. Therefore, this article aims at shedding some light on recent trends to correlate physical measures, such as the coefficient of friction derived by oral tribology, with prevailing theories on underlying physiological causes for sensory perception of wines. Some successful cases reported the potential of correlating wine astringency perception with the coefficient of friction in tribological experiments. Our critical assessment demonstrates that the findings are still contradictory, which urgently asks for more systematic studies. Therefore, we summarize the current challenges and hypothesize on future research directions with a particular emphasis on the comparability, reproducibility and transferability of studies using different experimental test-rigs and procedures.

Normal-phase chromatographic separation of pigmented wine tannin by nano-HPLC quadrupole time-of-flight tandem mass spectrometry and identification of candidate molecular features

BACKGROUND

As a wine ages, altered sensory properties lead to changes in perceived quality and value. Concurrent modifications of anthocyanin and tannin occur forming pigmented tannin, softening astringency and retaining persistent color. Wine tannin extracts of 1990 and 2010 vintages of Oakville Station Cabernet Sauvignon have been analyzed using normal-phase chromatography with tandem quadrupole time-of-flight mass spectrometry (QToF) to investigate the compositional differences in their pigmented tannin fractions.

RESULTS

The older wine demonstrates much greater structural diversity and a range of more polar compounds, while the younger wine contains fewer observed ion peaks. Several hundred molecular features are observable, and, as expected, there is progression to higher molecular weights after long aging. Between 7% and 16% of molecular features could be matched to a database of anticipated pigmented tannin compounds. Many signals had multiple possible isomeric identities, but fragmentation to resolve their identity was stymied by low sensitivity of the tandem mass spectrometric capability provided by QToF, so isomeric disambiguation is incomplete.

CONCLUSIONS

The chromatography displayed a high degree of resolution in aged wines, separating many of the known pigment types, including aldehyde bridged compounds, pyranoanthocyanins and direct condensation products among others, as well as resolving a great number of unknown compounds. Expanding our understanding of red wine pigments will lead to better wines as winemakers will be able to associate quality with particular wine pigment profiles once we can distinguish the relevant patterns in those pigments. © 2021 Society of Chemical Industry.

The Oxygen Consumption Kinetics of Commercial Oenological Tannins in Model Wine Solution and Chianti Red Wine

One property of oenological tannins, oxygen reactivity, is commonly exploited in winemaking. The reactivity is mediated by the presence of catalysts (i.e., transition metals and sulfur dioxide) and protects wine against oxidation. This work compares the oxygen consumption rate (OCR) of four commercial oenological tannins (two procyanidins from grape skin and seed, an ellagitannin from oak wood and a gallotannin from gallnut) in a model wine solution and Chianti red wine. All samples were subjected to consecutive cycles of air saturation at 20 °C to increase the total level of oxygen provided. After each cycle, the oxygen level was measured by means of a non-invasive luminescent sensor glued to a transparent surface (sensor dots) until there was no further change in substrate reactivity. The OCR followed first-order kinetics, regardless of the tannin. As expected, the ellagitannin showed the fastest OCR, followed by the two from grape seeds and skins and finally the gallotannin. The total O₂ consumption in the red wine was almost double that of the model solution, due to the oxidation of wine substrates. The measurement of OCR is helpful for setting up an advanced winemaking protocol that makes use of tannins to reduce the use of sulfur dioxide.

Rheological study of tannin and protein interactions based on model systems

The interaction between wine tannins and saliva proteins is responsible for wine astringency perception, producing a depletion of salivary proteins and changes on oral friction. In sensorial terms, astringency is described as a dryness and puckering sensation in the mouth, which is related to the "structure" or "body" of red wines. However, these last descriptors, as structure or body, are perceived during wine tasting and commonly related to wine viscosity. To address these differences on sensory response, we hypothesize that tannin-protein interactions could be a key factor involved in the viscosity of red wines/saliva mixtures, just as they are for astringency. We used a rheological method to study the impact of tannin-protein interaction on the viscosity of model wine-saliva systems. Mixtures of model saliva based on mucin and typical astringent compounds, as commercial tannins and gallic acid, were evaluated for their rheological behavior. The viscometric flow of the fluid mixtures was determined, and subsequently, the viscosity was evaluated at a shear rate of 60 s^-1 . It was observed that red wines/saliva mixtures exhibit non-Newtonian flow and ascending tannin doses led to an increase in the apparent viscosity. Nephelometric analysis demonstrate that tannin-mucin aggregates were formed, which suggests that these complexes were potentially responsible for the viscosity increases, modifying the rheological behavior of these mixtures. Results from this work propose that tannin-protein interactions are also involved in the underlying mechanism of thickness perception of red wines and rheology could be a complementary instrumental technique for wine mouthfeel characterization.

Human saliva and model saliva at bulk to adsorbed phases - similarities and differences

Human saliva, a seemingly simple aqueous fluid, is, in fact, an extraordinarily complex biocolloid that is not fully understood, despite many decades of study. Salivary lubrication is widely believed to be a signature of good oral health and is also crucial for speech, food oral processing and swallowing. However, saliva has been often neglected in food colloid research, primarily due to its high intra- to inter-individual variability and altering material properties upon collection and storage, when used as an ex vivo research material. In the last few decades, colloid scientists have attempted designing model (i.e. 'saliva mimicking fluid') salivary formulations to understand saliva-food colloid interactions in an in vitro set up and its contribution on microstructural aspects, lubrication properties and sensory perception. In this Review, we critically examine the current state of knowledge on bulk and interfacial properties of model saliva in comparison to real human saliva and highlight how far such model salivary formulations can match the properties of real human saliva. Many, if not most, of these model saliva formulations share similarities with real human saliva in terms of biochemical compositions, including electrolytes, pH and concentrations of salivary proteins, such as α-amylase and highly glycosylated mucins. This, together with similarities between model and real saliva in terms of surface charge, has led to significant advancement in decoding various colloidal interactions (bridging, depletion) of charged emulsion droplets and associated sensory perception in the oral phase. However, model saliva represents significant dissimilarity to real saliva in terms of lubricating properties. Based on in-depth examination of properties of mucins derived from animal sources (e.g. pig gastric mucins (PGM) or bovine submaxillary mucin (BSM)), we can recommend that BSM is currently the most optimal commercially available mucin source when attempting to replicate saliva based on surface adsorption and lubrication properties. Even though purification via dialysis or chromatographic techniques may influence various physicochemical properties of BSM, such as structure and surface adsorption, the lubricating properties of model saliva formulations based on BSM are generally superior and more reliable than the PGM counterpart at orally relevant pH. Comparison of mucin-containing model saliva with ex vivo human salivary conditioning films suggests that mucin alone cannot replicate the lubricity of real human salivary pellicle. Mucin-based multi-layers containing mucin and oppositely charged polyelectrolytes may offer promising avenues in the future for engineering biomimetic salivary pellicle, however, this has not been explored in oral tribology experiments to date. Hence, there is a strong need for systematic studies with employment of model saliva formulations containing mucins with and without polycationic additives before a consensus on a standardized model salivary formulation can be achieved. Overall, this review provides the first comprehensive framework on simulating saliva for a particular bulk or surface property when doing food oral processing experiments.

Effect of ethanol, glycerol, glucose and tartaric acid on the viscosity of model aqueous solutions and wine samples

Viscosity is a property that exerts great influence on the body of wines, since it affects the sensation of thickness in the mouth. The present study refers to the quantitative correlation of the major components of wine, alcohol, reduced sugar, glycerol and total acidity, in its viscosity. Various model aqueous solutions consisting of these components were prepared and viscosity was measured at 20 °C. Each component was studied either alone or in mixtures with the others. Viscosity of white dry wines samples was also measured. From the experimental results, linear multi-dependence equations were derived, which correlate the viscosity with the concentration of the components of the solutions, each of them alone and in combination. Glucose was found to affect viscosity of model aqueous solutions the most, whereas ethanol had the least effect. The knowledge of these factors may have a practical value in optimizing wine's body.

Oral Wine Texture Perception and Its Correlation with Instrumental Texture Features of Wine-Saliva Mixtures

Unlike solid food, texture descriptors in liquid food are scarce, and they are frequently reduced to the term viscosity. However, in wines, apart from viscosity, terms, such as astringency, body, unctuosity and density, help describe their texture, relating the complexity and balance among their chemical components. Yet there is uncertainty about which wine components (and their combinations) cause each texture sensation and if their instrumental assessment is possible. Therefore, the aim of the present work was to study the effect of wine texture on its main components, when interacting with saliva. This was completed by using instrumental measurements of density and viscosity, and by using two types of panels (trained and expert). For that, six different model-wine formulations were prepared by adding one or multiple wine components: ethanol, mannoproteins, glycerol, and tannins to a de-alcoholised wine. All formulations were mixed with fresh human saliva (1:1), and their density and rheological properties were measured. Although there were no statistical differences, body perception was higher for samples with glycerol and/or mannoproteins, this was also correlated with density instrumental measurements (R = 0.971, p = 0.029). The viscosity of samples with tannins was the highest due to the formation of complexes between the model-wine and salivary proteins. This also provided astringency, therefore correlating viscosity and astringency feelings (R = 0.855, p = 0.030). No correlation was found between viscosity and body perception because of the overlapping of the phenolic components. Overall, the present results reveal saliva as a key factor when studying the wine texture through instrumental measurements (density and viscosity).

Low Phenotypic Penetrance and Technological Impact of Yeast [GAR +] Prion-Like Elements on Winemaking

[GAR⁺] prion-like elements partially relieve carbon catabolite repression in Saccharomyces cerevisiae. They have been hypothesized to contribute to wine yeast survival and alcohol level reduction, as well as communication with bacteria and stuck fermentation. In this work, we selected [GAR⁺] derivatives from several genetic backgrounds. They were characterized for phenotypic penetrance, heritability and confirmed as prion-like through curing by desiccation. In terms of fermentation kinetics, the impact of the prion on anaerobic wine fermentation (natural grape juice) was either neutral or negative, depending on the genetic background. Likewise, residual sugars were higher or similar for [GAR⁺] as compared to the cognate [gar^-] strains. The prions had little or no impact on glycerol and ethanol yields; while acetic acid yields experienced the highest variations between [GAR⁺] and [gar^-] strains. Strains analyzed under aerobic conditions followed the same pattern, with either little or no impact on fermentation kinetics, ethanol or glycerol yield; and a clearer influence on volatile acidity. Although no clear winemaking advantages were found for [GAR⁺] strains in this work, they might eventually show interest for some combinations of genetic background or winemaking conditions, e.g., for reducing acetic acid yield under aerated fermentation.

Effect of sodium sulfite, tartaric acid, tannin, and glucose on rheological properties, release of aroma compounds, and color characteristics of red wine

In this study, we evaluated the effect of addition of non-volatile compounds (sodium sulfite, tartaric acid, tannin, and glucose) on the rheological properties, release of aroma compounds, and color of the red wine. While determining the rheological properties of the supplemented samples, non-Newtonian fluidic and shear-thinning behavior of samples was noticed. The viscosity of these samples was found in negative correlation with the dose of addition of various non-volatile substances. The aroma profile of red wine after additions showed the change in the release of the nine key aroma compounds. Among them ethyl hexanoate, phenylethyl alcohol, octanoic acid, diethyl succinate, and ethyl octanoate were profoundly increased. Further, the color of red wines was improved in the presence of tartaric acid and tannin. Overall, supplementation of various substances during storage period of three different wines could enormously affect the sensory characteristics in a dose dependent manner.

An integrative salivary approach regarding palate cleansers in wine tasting

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.

Aging-related changes in quantity and quality of saliva: Where do we stand in our understanding?

Saliva is crucial to oral processing of food and consequently is also related to the sensory and textural experience. It is often assumed that the secretion and properties of saliva change with age, which can result in dry mouth conditions, taste aberrations. Such changes may result in reduced nutrient intake and malnutrition besides adversely affecting the quality of life. Based on some recent research findings, this article reviews our current understandings on age-dependent changes on quantity (bulk salivary flow rate) as well as quality of saliva (e.g., composition, viscosity, lubrication) in healthy elderly individuals. The review begins with a short introduction to histological changes of salivary glands upon aging. This is followed by covering different aspects of salivary changes with key articles highlighting decreased flow rate, increased ionic concentration, decreased calcium and mucin content in saliva of elderly subjects consequently affecting the oral coating and flavor perception. We also highlight issues in data associated with respect to variance in saliva collection protocols as well as factors influencing such results other than age, such as health conditions and polypharmacy. Clear gaps in literature have been highlighted with respect to lack of quantitative data in viscoelasticity, rheology, and lubrication properties of saliva in healthy elderly population and the potential impact of changes in these material properties on sensory and textural perception of food and consequently food intake. Such insights will not only have clinical implications for maintaining optimal oral health in elderly population but also serve to optimize food for elderly population. PRACTICAL APPLICATIONS: The population has undergone a fundamental change in its age structure globally, with a rapid increase in elderly population. Innovation of tailored foods is still in its early stage to satisfy the needs of growing aging population. One of the biggest challenges in such food product development is lack of adequate understanding and characterization of endogenous factors, that is, age-related changes in saliva, which may influence oral processing of food and subsequently nutrient intake. Aging affects the salivary glands and alters quantity (flow rate) and quality (e.g., ion and protein composition, rheology, tribology) of saliva. Thus, older adults may suffer from dry mouth, taste aberration, and poor oral hygiene, greatly affecting their quality of life. This review provides insights into how age versus other health conditions influence salivary properties. Understanding of age-dependent changes in salivary rheology and tribology will be of paramount importance to optimize food for elderly population.