Tannin-salivary protein

Three-dimensional structure of wine tannin-salivary protein colloidal complexes... 

Herbivores that commonly feed on tannin-rich plants have evolved interesting methods to lessen the effect of ingested tannins on their digestive systems. For example, the salivary proteins of rabbits and other rodents are high in the amino acid proline, which has a very high affinity for tannins. Eating food high in tannins stimulates the secretion of these proteins and diminishes the toxic effect of the tannins. 

Browsers such as mule deer, 0. hcmionus, have proUne-rich salivary proteins that bind tannins this enables them to feed on tanniniferous plants (Robbins etal, 1991). By contrast, grazers such as sheep and cattle do not possess tanninbinding proteins (Austin etal, 1989 Robbins etal, 1991), and neither do mixed feeders such as goats (Distel and Provenza, 1991). Rat and mouse saliva also contain proline-rich proteins that bind tannins. In human saliva, about 70% of total protein is rich in proline (Fig. 11.9) (Mehansho etal, 1987). 

Dietz, B. A., Hagerman, A. E., and Barrett, G. W. (1994). Role of condensed tannin on salivary tannin-binding proteins, bioenergetics and nitrogen digestibility in Micro-tuspennsylvanicus. Journal of Mammalogy 75,880-889. 

Warner, T. F. and Azen, E. A. (1988). Tannins, salivary proline-rich proteins and oesophageal cancer. Medical Hypotheses 26,99-102. 

Sarni-Manchado, P., Cheynier, V., and Moutounet, M., Interactions of grape seed tannins with salivary proteins. J. Agric. Food Chem. 47, 42, 1999. 

Bacon, J.R. and Rhodes, M.J.C., Development of a competition assay for the evaluation of binding of human parotid salivary proteins to dietary complex phenols and tannins using a peroxidase-labeled tannin, J. Agric. Food Chem., 46, 5083, 1998. 

Hagerman, A.E. and Robbins, C.T., Specificity of tannin-binding salivary proteins relative to diet selection by mammals. Can. J. Zool, 71, 628, 1993. 

Despite their very short sequence (7 to 38 amino acid residues for the 12 histatins identified so far), the histidine-rich salivary protein histatins have also been reported to precipitate tannins, eventually more efficiently than proline-rich proteins, especially at neutral pH and high tannin concentration. A detailed NMR analysis of the binding between EGCG and histatin 5, a 24-mer that is very rich in basic His, Lys, and Arg residues ( 60%) and devoid of secondary structure, has revealed noncooperative binding of six to seven flavanol molecules with a dissociation constant of 1 mM (pH 3.0, 25°C). ... 

Charlton, A.J. et al.. Tannin interactions with a full-length human salivary protein display a stronger affinity than with single proline-rich repeats, FEBS Lett., 382, 289, 1996. 

Shimada T. 2006. Salivary proteins as a defense against dietary tannins. J Chem Ecology 32 1149-1163. 

Mole, S., Butler, L.G., and Iason, G., Defense against dietary tannin in herbivores a survey for proline rich salivary proteins in mammals, Biochem. Syst. and Ecol., 18, 287, 1990. 

Juntheikki, M.R., JulkunenTiitto, R., and Hagerman, A.E., Salivary tannin-binding proteins in root vole (Microtus oeconomus Pallas), Biochem. Syst. Ecol., 24, 25, 1996. 

Phenolic compounds also contribute directly to the flavor due to their astrin-gency and bitter taste characteristics [11]. In fact, astringency is believed to be due to the interaction between tannins and salivary proteins, resulting in the formation of protein-tannin aggregates in the mouth, as discussed in more detail below [12-15],... 

Some studies have been made relating specifically to astringency. Some of these studies have focused directly on interactions between tannins and salivary proteins [21, 23, 25, 46, 50-53], and on the changes in saliva protein composition after interaction with tannins [15, 38, 54, 55]. Other studies have correlated the sensorial astringency with protein-tannin interactions [45, 56, 57]. In fact, the astringency felt when sampling different tannin solutions can be correlated with the ability of these tannins to precipitate proteins. This effect has been observed with several proteins such as mucin [45], ovalbumin and gelatin [57], bovine semm albumin (BSA), and salivary proteins [58]. 

Interactions of Tannins with Salivary Proteins-Astringency 387... 

Some studies have shown that human a-amylase is inhibited [31, 95] or precipitated by tannins [46]. However, this enzyme can be protected from inhibition by tannins in the presence of other salivary proteins, such as histatins or PRPs, which is generally the case [40]. 

Salivary histatins have a high ability to precipitate tannins [18, 40, 71]. Histatins are histidine-rich proteins that can be found in both sublingal/submandibular saliva and parotid saliva and represent about 2.6% of the total salivary proteins. It has been proposed that histatins could be important in neutralizing tannins in situations where they come not from the diet but from other situations when the saliva is not stimulated, such as when cotton workers breathe tannin-rich dust [181-... 

Studies performed over the years have contributed to better understanding of the interactions between proteins and tannins, which are important not only due to their astringency but also because of their impact on food nutritional characteristics, on human health, and on plant metabolism. It is clear that protein-tannin interactions are influenced by several factors, among which polysaccharides could be important because they are also present in tannin-rich vegetables. Much remains to be studied in this field, particularly the specific phenomenon that occurs between proteins, tannins, and polysaccharides that leads to a decrease in aggregation, and further studies are needed involving other salivary proteins and digestive enzymes. 

This inhibition of the interactions between tannins and salivary protein by carbohydrates has been proposed to contribute to the loss of astringency during ripening of some fruits (Luck et al. 1994 Ozawa et al. 1987 Taira et al. 1997). 

Recently, Carvalho et al. (2006b) studied the influence of wine polysaccharides (AGP, RGll and MP) on salivary protein-tannin interactions. The results showed that the most acidic fractions of AGPs and MPs have the ability to inhibit the formation of aggregates between condensed tannins and two different salivary proteins (a-amylase and lB8c). The concentrations tested are below to those present in wine which means that they could have an influence in wine astringency. 

Apart from salivary proteins, other proteins have been used in the tannin-protein interaction studies due to some characteristics that make them similar to PRPs, like casein, gelatin, polyproline (Jobstl et al. 2004 Calderon et al. 1968 Luck et al. 1994 Poncet-Legrand et al. 2006 Siebert et al. 1996). Although it is not a protein, the polymer polyvinylpolypyrrolidone as also been used in these studies (Hagerman and Butler 1981 Laborde et al. 2006). Recently, an electronic tongue based on protein-tannin interactions has been developed to measure astringency (Edelmann and Lendl 2002). Despite the unquestionable importance of all these works to understand the interaction between tannins and proteins, extrapolation to the real context of wine sensory should be done with care. 

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