Wine phenolics: looking for a smooth mouthfeel

Alice Vilela^a, AntónioM. Jordão^b, Fernanda Cosme^a*

^aCQ-VR - Chemistry Research Centre, University of Trás-os-Montes and Alto Douro, School of Life Science and Environment, Edifício de Enologia, 5001-801 Vila Real, Portugal.

^bPolytechnic Institute of Viseu (CI&DETS), Agrarian Higher School, Estrada de Nelas, Quinta da Alagoa, Ranhados, 3500-606 Viseu, Portugal.

Fernanda Cosme, Wine phenolics: looking for a smooth mouthfeel(2016)SDRP Journal of Food Science & Technology 1(1)

Each grape variety has its own phenolic profile. However, the concentration of the phenolic compounds present in wine, are mainly dependent of the winemaking process. Phenolic compounds influence wine sensorial characteristics namely taste or mouthfeel, bitterness, astringency and color. Humans can perceive six basic tastes: sweet, salty; sour; umami; fat-taste and bitter taste. This last basic taste is considered as a defense mechanism against the ingestion of potential poisons. Some of the genes, encoding G-protein-coupled receptors - TAS2Rs, which translate for these distinct bitter compounds detectors have been identified. Different phenolic compounds activate distinguished combination of TAS2Rs. Astringency in wine is primarily driven by proanthocyanidins, soluble protein-proanthocyanidins complexes diminish the protective salivary film and bind to the salivary pellicle; insoluble protein-proanthocyanidins complex and proanthocyanidins are rejected against salivary film and trigger astringency sensation via increasing friction.
Thus, the aim of this review is to expand the knowledge about the role of wine phenolic compounds in wine sensorial properties, namely in bitterness and astringency phenomenon’s.

Wine is a hydroalcoholic acid solution containing various phenoliccompounds. They are present in seeds, skins and stems of the grapes; therefore their concentration in wine is highly affected by winemaking process such as fermentation/maceration lengthsin which extraction occurred.However, the grape variety used in winemakingis also an important factor that affects the wine phenolic composition, since each grape variety has its own phenolic profile (Jordão et al., 1998; Bautista-Ortin et al., 2007;Jordão and Correia, 2012; Costa et al., 2015).Wine phenolic compounds have an importantinfluence in wine sensorial characteristics. For example, monomeric (+)-catechins give bitter taste to wine, whereas polymers cause astringent Taste (Jackson, 2000; Oliveira et al., 2011).In red wine, phenoliccompoundslike, coumaric, caffeic, ferulic and vanillic acids are relatively simple structures while others are complex polymeric structures such as tannins, that can combine with numerous substances including polysaccharides, proteins, and other polyphenols,affectingmouthfeel,bitterness,  astringency and color. Anthocyanins and tannins influence the color and color stability of wine besides influencing mouthfeel, depth and astringency (Saint-Cricq de Gaulejac et al., 1998). These complex structures change over time; specifically during the wine aging process,becoming more complex due to the increase ofthe mean degree of polymerization(Suriano et al., 2015).

Wine phenolic composition

Wine contains manyphenolic substances, their major sources being grape stems, seeds and skins (Jordão et al., 2001; Cheynier, 2005). However, the wine phenolic composition is also determined by yeast metabolism, since they can form important wine color components, including anthocyanins adducts and pigmented polymers (Fulcrand et al., 1998; Benabdeljalil et al., 2000;Blazquez Rojas et al., 2012) or by the type of wine aging process, such as the use of oak wood barrels or oak wood fragments (De Coninck et al., 2006; Jordão et al. 2008). According to several authors (Ribéreau-Gayon et al., 2006; Jordão et al. 2012) the levels of polyphenolic compounds in red wine depended from several factors, namely the pomace-contact maceration time and the evolution profile of major polyphenol groups.

Wine phenolic compounds can be classified into two groups: flavonoids and nonflavonoids. The major C₆-C₃-C₆ flavonoids in wine include conjugates of the flavonols, quercetin, and myricetin; the flavan-3-ols (+)-catechin and(-)-epicatechin, and malvidin-3-glucoside and other anthocyanins. The nonflavonoids incorporate the C₆-C₁ hydroxy-benzoic acids, gallic and ellagic acids; the C₆-C₃ hydroxycinnmates caffeic, caftaric, and p-coumaric acids, and the C₆-C₂-C₆ stilbenes trans-resveratrol, cis-resveratrol, and trans-resveratrol glucoside (Waterhouse, 2002;Cosme and Jordão, 2014).

Total phenol content ranged in red wine from 1850-2200 mg/L and in white wine from 220-250 mg/L, being the flavonoid compounds the mainphenols in red wine, extracted from grape skins and seeds during the fermentation/maceration process (Waterhouse and Teissedre, 1997;Cristino et al., 2013).

Non-flavonoid phenolic compounds are present in wine at low concentration, and their origin could be from the grape pulp or oak wood barrels used in wine aging. The three main hydroxycinnamates in grapes and wine are those based on coumaric acid, caffeic acid and Ferulic acid. In grapes hydroxycinnamic acids exist as esters of tartaric acid and are p-coutaric acid, caftaric acid, and fertaric acid, respectively(Somers et al., 1987; Waterhouse, 2002).At the concentration found in wines, the hydroxycinnamates seem to have no perceptiblebitterness or astringency, since they are present below their sensory threshold (Verette et al., 1988).Hydroxybenzoic acids comprise p-hydroxybenzoic acid, syringic acid, vanillic acid and gallic acid.Gallic acidcould be also originated from the hydrolysisof gallate esters of hydrolyzable tannins and condensed tannin (Waterhouse and Teissedre, 1997; Waterhouse, 2002).

            Total monomeric flavan-3-olsin red wine rangedfrom 40–120mg/L, depending on the extraction process during vinification. However, condensed flavan-3-ol units the so calledcondensed tannins or proanthocyanidins (0.5g/L-1.5g/L in red and 10-50mg/L in white wine)are the main phenolic compounds in red wine (Waterhouse, 2002).In terms of sensorial perception, flavan-3-ols ((+)-catechin, (-)-epicatechin, (-)-epicatechin-3-O-gallate)can be bothbitter and astringent, however in polymerform bitterness is slight, but astringency remains (Su and Singleton 1969, Robichaud and Noble, 1990). Thus,tannins have an important role inwine astringency and also contribute to impart bitterness sensation.

Monomeric anthocyanins extracted from grapes are the main compounds responsible for the color of young red wines(Boulton, 2001).There are five anthocyanidins: cyanidin, peonidin, delphindin, petunidin and malvidin, which could be at the six-hydroxyl of the glucose, acyl substituted, with ester linkages connecting an acetyl group, a coumaryl group, and a lesser amount of caffeoyl group. There are also derivatives of anthocyanins that result by the interaction of anthocyanins with other molecules such as, vinyl catechol, pyruvic acid, vinyl phenol, acetone, α-ketoglutaric acid, 4-vinylguaiacol or glyoxylic acid (Pinho et al., 2012). For example, pyranoanthocyanins namely, vitisin-A and vitisin-B, are formed by the condensation of anthocyanin, malvidin-3-glucoside with the fermentation by-products pyruvicacid and acetaldehyde, respectively. These compounds are more stable and originate at pH 4.0 deeper colors than monomeric anthocyanins (Morata et al., 2007; Cano-López et al., 2008).During wine aging, polymerization reaction take place and polymeric pigments became responsible for wine color. It was observed that wine color changed from a bright red to a reddish-brown hue.This is associated to the formation of new and more stablepolymeric pigments resulting from reactions between anthocyanins and other phenolic compounds, for example, flavan-3-ol monomers and proanthocyanidins (Somers, 1971, Kantz and Singleton, 1991, Singleton and Trousdale, 1992; He et al., 2012).These reactions are based acetaldehyde mediated condensation, co-pigmentation and self-association reactions(Boulton 2001, Castillo-Sánchez et al., 2008). It is known that anthocyanins do not contribute to mouthfeel sensations; however they are able to contribute to mouthfeel when combined with other species in the form of polymers (Haslam, 1998).

Winemaking technology,including, fermentation temperature and lengths, as well as pH and alcoholconcentrationinfluence the wine phenolic concentration. Also, clarification and stabilization techniques used to achieve wine limpidityand stability result in a potential decrease of phenolic content (Mira et al., 2006; Gonçalves and Jordão, 2009; Lasanta et al., 2013; Guise et al., 2014: Ribeiro et al., 2014; Ibeas et al., 2015). For example, the use of fining agents such asgelatin, egg albumin, isinglass and casein/potassium caseinatealso could reducespecific phenolic compounds in function of the protein fining agent applied and couldlead to changes in color, bitterness and astringency in some wines (Cosme et al., 2007; Braga et al., 2007;Cosme et al., 2008; Cosme et al., 2009; Gonçalves and Jordão, 2009).

Bitterness or astringency?

Phenolic compounds are responsible for bitterness and astringency of many foods and beverages, including wine (Bravo, 1998; Gawel, 1998). Whereas lower-molecular-weight phenolic compounds tend to be bitter, higher-molecular-weight polymers are more likely to be astringent (Noble, 1994). Astringency (drying or puckering mouth feel detectable throughout the oral cavity), may be due to a complexing reaction between polyphenols and proteins of the mouth and saliva (Noble, 1994).

            High-molecular-weight polyphenols or tannins have long been regarded as antinutrients because they interfere with protein absorption or reduce iron availability, they complex with proteins, starches, and digestive enzymes and are thought to reduce the nutritional value of foods (Chung et al., 1998).

Phenolic compounds in wine range from low-molecular weight-catechins to high-molecular-weight tannins (Blanco et al., 1998). As referred by Drewnowski and Gomez-Carneros (2000) perceived bitterness and astringency increased as a linear function of concentration for (+)-catechin and for grapeseed tannin. Flavonoid monomers such as (+)-catechin and (-)-epicatechin were rated as more bitter than astringent (Thorngate and Noble, 1995). At higher molecular weights, (+)-catechin polymers became progressively more astringent. Thus, wine polyphenols with molecular weights >500, such as grape-seed tannin, were more astringent than bitter (Peleg et al., 1999).

            Kallithraka et al. (1997) realized a sensory study of (+)-catechins in a wine model system similar, in composition, to a dry table wine. The results obtained showed that (-)-epicatechin was significantly more bitter and astringent than (+)-catechin. In this study, tasters associated bitterness and astringency with perceived mouth drying and with mouth roughening, especially in higher concentrations of (-)-epicatechin.

            Phenols in wine are largely derived from grape skins (30%) and seeds (70%) that remain in contact with fermenting grape juice from 24 to 36 hours for rosé wines and from 4 to 21 days for red wines. Phenolic content of red wines can thus reach 1000–3.500 mg/L, depending on processing conditions (Chandrashekar et al., 2000; Blanco et al., 1998). However, the bitterness of phenolics is reduced by sucrose and is substantially enhanced by ethanol (Noble, 1994). In fact, Lanier et al. (2005) found that some people experience more bitterness when drinking more alcoholic beverages. This phenomenon is directly related to the genes they've inherited and, individual differences in bitterness and sweetness are predictors of alcohol liking and intake in young adults (Lanier et al., 2005). Actually, as previously reviewed by Jordão et al. (2015),consumers know that wines with high alcohol content can cause a gustatory disequilibrium affecting wine sensory perceptions leading to unbalanced wines. Multiple studies (Wooding et al., 2004; Drayna et al., 2003) have linked variation in TAS2R (taste receptor, type 2) bitter receptor genes, to alcohol intake.

Mechanism of bitter taste perception

The primary organ responsible for the sense of taste is the tongue, which contains the taste receptors to identify non-volatile chemicals in foods and beverages. Taste-stimuli are typically released when food is masticated and dissolved into saliva (pre-digested by oral enzymes, such as amylase, lipase, and proteases (Pedersen et al., 2002)).The taste buds, in the tongue,are located in structures called ‘papillae’. These structuresarethe first stage of gustatory signal processing.Cells within a bud communicate with one another, including electric coupling via gap junctions and cell to cell chemical communication via glutamate, serotonin, and ATP (Breslin and Spector,2008; Roper, 2013).

            Humans perceive nutrientsand toxins qualitatively as sweet (elicited by sugars); salty (elicited by sodium ion - Na⁺, and other ions reflecting mineral content); sour (elicited by free hydrogen ions - H⁺); savory or umami (elicited by glutamate and other amino acids), fat taste - elicited by products of fats and fatty acids (Keast and Costanzo, 2015) and bitter tasting - reflecting potential toxins in foods (Breslin and Spector, 2008). This last basic taste modality (bitter taste) may be considered as a defense mechanism against the ingestion of potential poisons, since numerous harmful compounds, including inorganic ions and rancid fats, secondary plant metabolites like alkaloids, synthetic chemicals do taste bitter (Meyerhof et al., 2005).

            The chemical detectors of the bitter compounds in the tongue canrecognize thousands of different chemicals. Some of the genes that translate for these distinct bitter compounds detectors have been identified (Adler et al., 2000; Bufe et al., 2002). These genes encoding G-protein-coupled receptors, TAS2Rs (previously referred to as T2Rs or TRBs), have been suggested to represent bitter taste receptors and are responsible for bitter taste transduction mechanism. An important gene contributing to PTC (the ability to taste the bitterness of phenylthiocarbamide) TAS2R38—taste receptor, type 2, member 38, perception has been identified. The gene located on chromosome 7q36, is a member of the bitter taste receptor family (Duffy et al., 2004).

Recently, it was evidenced by Soares et al.(2013) that different phenolic compounds activate distinguished combination of TAS2Rs: (-)-epicatechin stimulated threereceptors (TAS2R4, TAS2R5, and TAS2R39) while pentagalloylglucose activated two receptors(TAS2R5 and TAS2R39). Only one receptor was responded to malvidin-3-glucoside and procyanidin trimer.

The bitterness transduction mechanisms is schematized in Figure 1: Initially, bitter ligands activate TAS2Rs causing a conformational change. The active G-protein, transducin,activates enzyme phospholipase C(PLC-b2) to generate from to breakdown of phosphatidylinositol biphosphate (PIP₂)the second messenger - inositol triphosphate (IP₃), initiating the release of Ca²⁺from intracellular stores (vacuoles). TrpM5 is activated by elevated Ca²⁺ to flow in Na⁺, resulting in depolarization of receptor cell. The combined action of elevated Ca²⁺ and membrane depolarization opens the pannexin 1 hemichannel torelease transmitters to brain. Adenosine triphosphate (ATP) is secreted to gustatory afferent glossopharyngeal nerve fibers and ultimately generates a nerve signal in the brain recognized as a bitter taste (Ma et al., 2014).

In wines, in contrary to astringency, a gradual reduction of bitterness is perceived as their molecular weight augments (Noble, 1994).In grapesthere are evidences of different proportions of galloyl groupbetween the seed and skin fraction. The seed fraction with a higher proportion of galloyl group and a lower mean degree of polymerization (mDP)seems to be perceived as more bitterthan the skin fraction (Brossaud et al., 2001).

Mechanisms for astringency

Astringency refers to “the complex of sensations due to shrinking, drawing or puckering of the epithelium as a result of exposure to substances such as alums or tannins” (ASTM, 2004). Astringency could be stimulated by salts of multivalent metallic cations, dehydrating agents like ethanol, mineral and organic acids, tannins and small polyphenols (Bajec and Pickering, 2008). However, in wine, astringency is primarily driven by proanthocyanidins,also called condensed tannins(Sáenz-Navajas et al., 2012; Brandão et al., 2014).

            The mechanism for astringency was first proposed by Bate-Smith(1954) and is believed to be due to the ability of tannins to bind andprecipitate salivary proteins. The loss of lubrication in the oral cavity, including the tongue,occurs when tannins pass by and they bond to salivary proteins forming insoluble tannin–protein precipitates in the mouth, increasing friction which results in the sensation of astringency (Baxter et al. 1997).The general accepted mechanism for protein−tannin interaction was proposed by Siebert et al. (1996). Concerning this mechanism, a protein has a fixed number ofsites to which a tannin can bind. According to the ratio of protein or tannin used, different protein−tannin complexes are formed. According to Charlton et al. (2002), proteins and polyphenols combine to form soluble complexes, but when they grow to colloidal size particles, they become larger, leading to sediment formation.

            Charlton et al. in 2002 proposed a 3-stage model of the interaction between tannins and proteins: Initially, hydrophobic associations (π–π) occur between the planar surfaces of the tannin aromatic rings and hydrophobic sites of proteins such as pyrrolidine rings of prolyl residues. Simultaneously, hydrogen bonding effect assists to stabilize the complexes, occurring between the hydroxyl group of tannins and H-acceptor sites (carbonyl and –NH₂ groups) of proteins. Next, the protein-tannin complexes self-associate via further hydrogen bonding to produce soluble larger protein-tannin complexes and then aggregate. Finally, the aggregated complexes are large enough to form insoluble sediment and precipitate from solution.

            However, several authors supported the idea that “tannin–protein interaction” is more closely associated with astringency than “tannin–protein precipitation” (Obreque-Slier et al., 2010). Recently, Lee et al. (2012) demonstrated that PRPs (proline-rich proteins) precipitated tannins and alum except for hydrochloric acid while mucins mainly consisting the coating of epithelium tissues were able to precipitate acid and alum except for tannins. Thus, a disturbance of oral lubricating coatings may contribute to the increase of astringency. The loss of oral lubricating films/pellicle allows soluble tannin–protein aggregates or free astringent stimuli to interact directly with oral tissue possibly through receptors. The disturbance of the protective salivary film, could also be the explanation for the dry mouth perception usually associated with the astringent mouth-feel (Ma et al., 2014). According to Brandão et al. (2014), salivary proteins families have relative discriminatory functions in rating the perception of astringency depending on the type of astringent stimuli used. They show that repeated stimulations withprocyanidins may differently affect the several families of salivary proteins, suggesting that they could be involved in different stages of the development of astringency. Furlan et al. (2014) recently studied the interactionbetween monomeric flavan-3-ols and lipid liposomes, indicating that astringency sensation may also implicate the binding between red wine tannins and oral cavity membrane. Gibbins and Carpenter (2013) showed a multiple-modal system by which implicates several possible astringency mechanisms.

This review evidenced the important role of phenolic compounds on the wine sensory characteristics. Therefore, tannin and anthocyanin management during grape-growing by following phenolic maturity of red grapes and during winemaking is avery important factor, for tailoring the wine sensorial characteristics namely taste or mouthfeel, bitterness, astringency and color.

1. Adler, E., Hoon, M.A., Mueller, K.L., Chandrashekar, J., Ryba, N.J., Zuker, C.S. (2000). A novel family of mammalian taste receptors. Cell, 100, 693?702. 80705-9

   View Article           

2. ASTM. (2004). Standard definitions of terms relating to sensory evaluation of materials and products. In Annual book of ASTM standards. Philadelphia: American Society for Testing and Materials.

3. Bajec, M.R., Pickering G.J. (2008). Astringency: Mechanisms and Perception. Critical Reviews in Food Science and Nutrition, 48, 858-875. PMid:18788010

   View Article      PubMed/NCBI     

4. Bate-Smith, E.C. (1954). Astringency in foods. Food Chemistry, 23, 124-135. http://www.ncbi.nlm.nih.gov/pubmed/9154941 https://www.researchgate.net/publication/280801625_Evidence_of_new_pigments_resulting_from_reaction_between_anthocyanins_and_yeast_metabolites http://link.springer.com/chapter/10.1007%2F978-1-4899-1925-0_27 http://link.springer.com/article/10.1007%2Fs11274-012-1142-y

   View Article           

5. Bautista-Ortin, A.B., Fernandez?Fernandez, J.I., Lopez-Roca, J.M., Gomez-Plaza, E. (2007). The effects of enological practices in anthocyanins, phenolic compounds and wine color and their dependence on grape characteristics. Journal of Food Composition and Analysis,20, 546?552.

   View Article           

6. Baxter, N.J., Lilley, T.H., Haslam, E., Williamson, M.P. (1997). Multiple interactions between polyphenols and a salivary prolinerich protein repeat result in complexation and precipitation. Biochemistry, 36, 5566-5577. PMid:9154941

   View Article      PubMed/NCBI     

7. Benabdeljalil, C, Cheynier, V, Fulcrand, H, Hakiki, A, Mosaddak, M, Moutounet, M (2000). Evidence of new pigments resulting fromreaction between anthocyanins and yeast metabolites. Sciences des Aliments, 20, 203?220.

   View Article           

8. Blanco, V.Z., Auw, J.M., Sims, C.A., O'Keefe, S.F. (1998). Effect of processing on phenolics of wines. Advances in Experimental Medicine and Biology, 434, 327?40.

   View Article           

9. Blazquez Rojas, I., Smith, P.A., Bartowsky, E.J. (2012). Influence of choice of yeasts on volatile fermentation-derived compounds, colour and phenolics composition in Cabernet Sauvignon wine. World Journal of Microbiology and Biotechnology, 28, 3311?3321. PMid:22878903

   View Article      PubMed/NCBI     

10. Boulton, R. (2001). The copigmentation of anthocyanins and its role in the colour of red wine: A critical review. American Journal of Enology and Viticulture, 52, 67?87. http://iwrdb.org/cgi-bin/koha/opac-detail.pl?biblionumber=39144&shelfbrowse_itemnumber=31464

    View Article           

11. Braga, A., Cosme, F., Ricardo-da-Silva, J., Laureano, O. (2007). Gelatine, casein and potassium caseinate as wine fining agents: effect on colour, phenolic compounds and sensory characteristics. Journal International des Sciences de la Vigne et du Vin 41, 203-214.

    View Article           

12. Brand?o, E., Soares, S., Mateus, N., Freitas, V. (2014). In Vivo Interactions between Procyanidins and Human Saliva Proteins: Effect of Repeated Exposures to Procyanidins Solution. Journal of Agricultural and Food Chemistry, 62, 9562?9568. PMid:25198944

    View Article      PubMed/NCBI     

13. Bravo, L. (1998). Polyphenols: chemistry, dietary sources, metabolism, and nutritional significance. Nutrition Reviews, 56, 317?33. PMid:9838798

    View Article      PubMed/NCBI     

14. Breslin, P.A., Spector, A.C. (2008). Mammalian taste perception. Current Biology, 18, R148?R155. PMid:18302913

    View Article      PubMed/NCBI     

15. Brossaud, F., Cheynier, V., Noble, A.C. (2001). Bitterness and astringency of grape and wine polyphenols. Australian Journal of Grape and Wine Research, 7, 33-39.

    View Article           

16. Bufe, B., Hofmann, T., Krautwurst, D., Raguse, J.D., Meyerhof, W. 2002. The human TAS2R16 receptor mediates bitter taste in response to beta-glucopyranosides. Nature Genetics, 32, 397?401. PMid:12379855

    View Article      PubMed/NCBI     

17. Cano-L?pez, M., Pardo-M?nguez, F., Schmauch, G., Saucier, C., Teissedre, P.-L., L?pez-Roca, L. M., G?mez-Plaza, E. (2008). Effect of micro-oxygenation on color and anthocyanin-related compounds of wine with different phenolic contents. Journal of Agricultural and Food Chemistry, 56, 14, 5932?5941. PMid:18558704

    View Article      PubMed/NCBI     

18. Castillo-S?nchez, J.X., Garc?a-Falc?n, M.S., Garrido, J., Mart?nez-Carballo, E., Martins-Dias, L.R., Mejuto, X.C. (2008). Phenolic compounds and colour stability of Vinh?o wines: Influence of wine-making protocol and fining agents. Food Chemistry, 106, 18-26.

    View Article           

19. Chandrashekar, J., Mueller, K.L., Hoon, M.A., Adler, E., Feng, L., Guo, W., Zuker, C.S., Ryba, N.J. (2000). T2Rs function as bitter taste receptors. Cell, 100, 703?11. 80706-0

    View Article           

20. Charlton, A.J.; Baxter, N.J.; Khan, M. L.; Moir, A.J.G.; Haslam, E.; Davies, A.P.; Williamson, M.P. 2002. Polyphenol/peptide binding and precipitation. Journal of Agricultural and Food Chemistry, 50, 1593?1601. PMid:11879042

    View Article      PubMed/NCBI     

21. Cheynier, V. (2005). Polyphenols in food are more, complex than often thought. American Journal of Clinical Nutrition, 81, 223S-229S. PMid:15640485

    PubMed/NCBI     

22. Chung, K.T., Wong, T.Y., Wei, C.I., Huang, Y.W., Lin, Y. (1998). Tannins and human health: a review. Critical Reviews in Food Science and Nutrition, 36, 421?64. PMid:9759559

    View Article      PubMed/NCBI     

23. Cosme, F., Jord?o, A.M. (2014). Grape phenolic composition and antioxidant capacity. In: Wine: Phenolic Composition, Classification and Health Benefits. Editor Youssef El Rayess. Nova Science Publishers, ISBN: 978-1-63321-048-6. pp: 1-40.

24. Cosme, F., Ricardo-da-Silva, J. Laureano, O. (2007). Protein fining agents: characterization and red wine fining assay. Italian Journal of Food Science, 19, 39-56.

25. Cosme, F., Ricardo-da-Silva, J. Laureano, O. (2008). Interactions between protein fining agents and proanthocyanidins in white wine. Food Chemistry, 106,536-544.

    View Article           

26. Cosme, F., Ricardo-da-Silva, J., Laureano, O. (2009). Behavior of Various Proteins on Wine Fining: Effect on Different Molecular Weight Proanthocyanidin Fractions of Red Wine. American Journal of Enologia and Viticultura, 112:197-204.

27. Costa, E., Cosme, F., Rivero-P?rez, M.D., Jord?o, A.M., Gonz?lez-SanJos?, M.L. (2015). Influence of wine region provenance on phenolic composition, antioxidant capacity and radical scavenger activity of traditional Portuguese red grape varieties. European Food Research and Technology, 241, 61-73.

    View Article           

28. Cristino, R., Costa, E., Cosme, F., Jord?o, A.M. (2013). General phenolic characterization, individual anthocyanin and antioxidant capacity of matured red wines from two Portuguese appellations of origins. Journal of the Science of Food and Agriculture, 93, 2486-2493. PMid:23460089

    View Article      PubMed/NCBI     

29. De Coninck, G., Jord?o, A.M., Ricardo-da-Silva, J.M., Laureano, O. (2006). Evolution of phenolic composition and sensory properties in red wine aged in contact with Portuguese and French oak wood chips. Journal International des Sciences de la Vigne et du Vin, 40, 25-34.

    View Article           

30. Drayna, D., Coon, H., Kim, U.K., Elsner, T., Cromer, K., Otterud, B., Baird, L., Peiffer, A.P., Leppert, M. (2003). Genetic analysis of a complex trait in the Utah Genetic Reference Project: A major locus for PTC taste ability on chromosome 7q and a secondary locus on chromosome 16p. Human Genetics, 112, 567?572. PMid:12624758

    PubMed/NCBI     

31. Drewnowski, A., Gomez-Carneros, C. (2000). Bitter taste, phytonutrients, and the consumer: a review. American Journal of Clinical Nutrition, 72, 1424?35. PMid:11101467

    PubMed/NCBI     

32. Duffy, V.B., Davidson, A.C., Kidd, J.R., Kidd, K.K., Speed, W.C., Pakstis, A.J., Reed, D.R., Snyder, D.J., Bartoshuk, L.M. (2004). Bitter receptor gene (TAS2R38), 6-n-propylthiouracil (PROP). Bitterness and alcohol intake. Alcoholism Clinical and Experimental Research, 28, 1629?1637. PMCid:PMC1397913

    View Article           

33. Fulcrand, H., Benabdeljalil, C., Rigaud, J., Cheynier, V., Moutounet, M. (1998) A new class of wine pigments generated by reactionbetween pyruvic acid and grape anthocyanins. Phytochemistry47, 1401?1407. 00772-3

    View Article           

34. Furlan, A. L., Castets, A., Nallet, F., Pianet, I., Grelard, A., Dufourc, E. J., G?an, J. (2014). Red wine tannins fluidify and precipitate lipid liposomes and bicelles. A role for lipids in wine tasting? Langmuir, 30, 5518-5526. PMid:24787144

    View Article      PubMed/NCBI     

35. Gawel, R. (1998). Red wine astringency: a review. Australian Journal of Grape and Wine Research, 4, 74?95.

    View Article           

36. Gibbins, H. L., Carpenter, G. H. (2013). Alternative mechanisms of astringency - what is the role of saliva? Journal of Texture Studies, 44, 364-375.

    View Article           

37. Gon?alves, F.J., Jord?o, A.M. (2009). Influence of different commercial fining agents on proanthocyanidin fraction and antioxidant activity of a red wine from baga grapes. Journal Inter national des Sciences de la Vigne et du Vin, 43, 111-120.

    View Article           

38. Guise, R., L. Filipe-Ribeiro, D. Nascimento, O. Bessa, F.M. Nunes, F. Cosme. (2014). Comparison between different types of carboxylmethylcellulose and other oenological additives used for white wine tartaric stabilization. Food Chemistry, 156, 250-257. PMid:24629965

    View Article      PubMed/NCBI     

39. Haslam, E.(1998). Practical polyphenolics from structure to molecular recognition and physiological action. Cambridge University Press, Cambridge.

40. He, F., Liang N.-N., Mu, L., Pan, Q.-H., Wang, J., Reeves,M.J.,Duan, C.-Q. (2012). Anthocyanins and Their Variation in Red Wines II. Anthocyanin Derived Pigments and Their Color Evolution. Molecules, 17, 1483-1519. PMid:23442981

    View Article      PubMed/NCBI     

41. Ibeas, V., Correia, A.C., Jord?o, A.M. (2015). Wine tartrate stabilization by different levels of cation exchange resin treatments: impact on chemical composition, phenolic profile and organoleptic properties of red wines. Food Research International, 69, 364-372.

    View Article           

42. Jackson, R.S. (2000). Wine Science Principles, Practice, Perception (Second ed.). SanDiego: Academic Press.

43. Jord?o, A.M., Correia, A.C. (2012). Relationship between antioxidant capacity, proanthocyanidin and anthocyanin content during grape maturation of Touriga Nacional and Tinta Roriz grape varieties. South African Journal of Enology and Viticulture, 33, 214-224.

44. Jord?o, A.M., Ricardo-da-Silva, J.M., Laureano, O. (1998). Evolution of anthocyanins during grape maturation of two varieties (Vitis vinifera L.): Castel?o Franc?s and Touriga Francesa. Vitis, 37, 93-94.

45. Jord?o, A.M., Ricardo-da-Silva, J.M., Laureano, O. (2001). Evolution of catechin and procyanidin composition during grape maturation of two varieties (Vitis vinifera L.) Castel?o Franc?s and Touriga Francesa. American Journal of Enology and Viticulture, 52, 230-234.

46. Jord?o, A.M., Ricardo-da-Silva, J.M., Laureano, O., Mullen, W., Alan, C. (2008). Effect of ellagitannins, ellagic acid and some volatile compounds from oak wood on the (+)-catechin, procyanidin B1 and malvidin-3-glucoside content of model wine solutions. Australian Journal of Grape and Wine Research, 14, 260?270.

    View Article           

47. Jord?o, A.M., Sim?es, S., Correia, A.C., Gon?alves, F.J. (2012). Antioxidant activity evolution during Portuguese red wine vinification and their relation with the proanthocyanidin and anthocyanin composition. Journal of Food Processing and Preservation, 36, 298-309.

    View Article           

48. Jord?o, A.M., Vilela, A., Cosme, F. (2015). From Sugar of Grape to Alcohol of Wine: Sensorial Impact of Alcohol in Wine. Beverages, 1, 292-310.

    View Article           

49. Kallithraka, S., Bakker, J., Clifford, M.N. (1997). Evaluation of bitterness and astringency of (+)-catechin and (-)-epicatechin in red wine and in model solutions. ournal of Sensory Studies, 12, 25?37.

    View Article           

50. Kantz, K., Singleton, V.L. (1991). Isolation and determination of polymeric polyphenols in wines using Sephadex LH-20. American Journal of Enology and Viticulture, 42, 309?316

51. Keast, R.S.J., Costanzo, A. (2015). Is fat the sixth taste primary? Evidence and implications. Flavour. 4:5 ( ), 7 pages.

    View Article           

52. Lanier, S.A., Hayes, J.E., Duffy, V.B. (2005). Sweet and bitter tastes of alcoholic beverages mediate alcohol intake in of-age undergraduates. Physiology & Behavior, 83, 821-31. PMid:15639168

    View Article      PubMed/NCBI     

53. Lasanta, C., Caro, I., P?rez, L. (2013). The influence of cation exchange treatment on the final characteristics of red wines. Food Chemistry, 138, 1072-1078. PMid:23411216

    View Article      PubMed/NCBI     

54. Lee, C.A., Ismail, B., Vickers, Z.M. (2012). The role of salivary proteins in the mechanism of astringency. Journal of Food Science, 77, C381-C387. PMid:22515235

    View Article      PubMed/NCBI     

55. Ma, W., Guo, A., Zhang, Y., Wang. H., Liu, Y., Li, H. (2014). A review on astringency and bitterness perception of tannins in wine Trends in Food Science and Technology, 40, 6?19.

    View Article           

56. Meyerhof, W., Behrens, M., Brockhoff, A., Bufe, B., Kuhn, C. (2005). Human Bitter Taste Perception. Chemical Senses, 30 (suppl 1), i14-i15.

    View Article           

57. Mira, H., Leite, P., Ricardo-da-Silva, J., Curvelo-Garcia, A.S. (2006). Use of ion exchange resins for tartrate wine stabilization. Journal International des Sciences de la Vigne et du Vin, 40, 223-246

    View Article           

58. Morata, A., Calder?n, F., Gonz?lez, M.C., G?mez-Cordov?s, M.C., Su?rez, J.A. (2007). Formation of the highly stable pyranoanthocyanins (vitisins A and B) in red wines by the addition of pyruvic acid and acetaldehyde. Food Chemistry, 100, 1144-1152.

    View Article           

59. Moyes, C.D., Schulte, P.M. (2008). Principles of Animal Physiology (2nd Edition), Pearson/Benjamin Cummings, 754 pp.

60. Noble, C.A. (1994). Bitterness in wine. Physiology and Behavior, 56:1251?5. 90373-5

    View Article           

61. Obreque-Slier, E., L?pez-Sol?s, R., Pe-a-Neira, ?., Zamora-Mar?n, F. (2010). Tannine-protein interaction is more closely associated with astringency than tannine-protein precipitation: experience with two oenological tannins and a gelatin. International Journal of Food Science and Technology, 45, 2629-2636.

    View Article           

62. Oliveira, C.M., Ferreira, A.C.S., De Freitas, V., Silva, A.M.S. (2011). Oxidation mechanisms occurring in wines. Food Research International, 44, 1115-1126.

    View Article           

63. Pedersen, A.M., Bardow, A., Jensen, S.B., Nauntofte, B. (2002). Saliva and gastrointestinal functions of taste, mastication, swallowing and digestion. Oral Diseases, 8, 117?129. PMid:12108756

    View Article      PubMed/NCBI     

64. Peleg, H., Gacon, K., Noble, A.C. (1999). Bitterness and astringency of flavan-3- ol monomers, dimers and trimers. Journal of the Science of Food and Agriculture, 79, 1123?8. 1097-0010(199906)79:8<1123::AID-JSFA336>3.0.CO;2-D

    View Article           

65. Pinho, C., Couto, A. I., Valent?o, P., Andrade, P., Ferreira, I.M.P.L.V.O. (2012). Assessing the anthocyanic composition of Port wines and musts and their free radical scavenging capacity. Food Chemistry, 131, 885-892.

    View Article           

66. Ribeiro, T., Fernandes, C., Nunes, F. M., Filipe-Ribeiro, L., Cosme, F. (2014). Influence of the structural features of commercial mannoproteins in white wine protein stabilization and chemical and sensory properties. Food Chemistry, 159:47-54. PMid:24767025

    View Article      PubMed/NCBI     

67. Rib?reau-Gayon P, Glories Y, Maujean A, Dubourdieu D. 2006. Handbook of Enology. The Chemistry of Wine Stabilization and Treatments. (2nd ed.). (Vol. 2). France: Bordeaux. Wiley & Sons Ltd., Chichester, England

    View Article           

68. Robichaud, J.L., Noble,A.C. (1990). Astringency and bitterness of selected phenolicsin wine. Journal of the Science of Food and Agriculture, 53: 343?353.

    View Article           

69. Roper, S.D. (2013). Taste buds as peripheral chemosensory processors. Seminars in Cell and Developmental Biology, 24, 71? 79. PMid:23261954 PMCid:PMC3690797

    View Article      PubMed/NCBI     

70. S?enz-Navajas, M. P., Avizcuri, J.M., Ferreira, V., Fern?ndez-Zurbano, P. (2012). Insights on the chemical basis of the astringency of Spanish red wines. Food Chemistry, 134, 1484-1493. PMid:25005971

    View Article      PubMed/NCBI     

71. Saint-Cricq de Gaulejac, N., Glories, Y., Vivas, N. (1998). Recherche des composes responsables de l'efft antiradicalaire dans les vins. Journal des sciences et techniques de la tonnellerie, 4, 147-161.

72. Siebert, K.J., Troukhanova, N.V., Lynn, P.Y. (1996). Nature of polyphenol-protein interactions. Journal of Agricultural and Food Chemistry, 44, 80?85.

    View Article           

73. Singleton, V.L., Trousdale, E.K. (1992). Anthocyanin-tannin interactions explaining differences in polymeric phenols between white and red wines. American Journal of Enology and Viticulture, 43, 63?70

74. Soares, S., Kohl, S., Thalmann, S., Mateus, N., Meyerhof, W., De Freitas, V. (2013). Different phenolic compounds activate distinct human bitter taste receptors. Journal of Agricultural and Food Chemistry, 61, 1525-1533. PMid:23311874

    View Article      PubMed/NCBI     

75. Somers, T.C. (1971). The polymeric nature of wine pigments. Phytochemistry, 10, 2175?86 97215-7

    View Article           

76. Somers, T.C., Verdette, E., Pocock, K.F. (1987). Hydroxycinnamate esters of Vitis vinifera: Changes during white vinification and effects of exogenous enzymatic hydrolysis. Journal of the Science of Food and Agriculture, 40, 67-78.

    View Article           

77. Su, C.T., Singleton, V.L. (1969). Identification of three flavan-3-ols from grapes. Phytochemistry, 8, 1553-1558. 85929-4

    View Article           

78. Suriano, S., Alba, V., Tarricone, L., Di Gennaro, D. (2015). Maceration with stems contact fermentation: Effect on proanthocyanidins compounds and color in Primitivo red wines. Food Chemistry, 177, 382-389. PMid:25660901

    View Article      PubMed/NCBI     

79. Thorngate, J.H., Noble, A.C. (1995). Sensory evaluation of bitterness and astringency of 3R (-)-epicatechin and 3S (+)-catechin. Journal of the Science of Food and Agriculture, 67,531?35.

    View Article           

80. Verette, E., Noble, A.C., Somers, C. (1988). Hydroxycinnamates of Vitis vinifera: sensory assessment in relation to bitterness in white wine. Journal of the Science of Food and Agriculture, 45, 267?272.

    View Article           

81. Waterhouse, A. L. (2002). Wine Phenolics. Annals New York Academy of Sciences, 957, 21?36

    View Article           

82. Waterhouse, A.L., Teissedre,P.L. (1997). Levels of phenolics in California varietalwine. In Wine: Nutritional and Therapeutic Benefits. T. Watkins, Ed.: 12?23. AmericanChemical Society. Washington, DC.

    View Article           

83. Wooding, S., Kim, U.K., Bamshad, M.J., Larsen, J., Jorde, L.B., Drayna, D. (2004). Natural Selection and Molecular Evolution in PTC, a Bitter-Taste Receptor Gene. The American Journal of Human Genetics, 74, 637?646. PMid:14997422 PMCid:PMC1181941

    View Article      PubMed/NCBI