Tannins concentration

FIGURE 11.19 Condensed tannin concentrations in plants eaten to various degrees by giant tortoises on Adabra Island. (After Swain, 1979.)... 

Smith, K.E. and Kelman, W.M., Predicting condensed tannin concentrations in Lotus uliginosus Schkuhr using near-infrared reflectance spectroscopy, J. Scl Food Agric., 75, 263, 1997. Goodchild, A.V., El Haramein, E.J., and Abd El Moneim, A., Prediction of phenolics and tannins in forage legumes by near infrared reflectance, J. Near Infrared Spectrosc., 6, 175, 1998. 

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). ... 

Figure 16.8 shows a typical flow nephelometric graphic involving the interactions between three substrates protein, tannin, and carbohydrate. In an initial phase there is an increase in turbidity corresponding to the stabilization of protein and tannin concentrations. The maximum value of turbidity corresponds to the TSA of the tannin solution in relation to the protein (BSA). In a second phase a gradient of increasing carbohydrate concentration is started, leading to a decrease... 

Some recent evidences have shown that a basic PRP binds condensed tannins much more effectively than a-amylase. In Figure 16.10, it can be seen that the light-scattering intensity caused by aggregation increases with the concentration of procyanidins until a maximum after which the light scattered intensity remains constant even with a further increase in tannin concentration. 

Cut wells of 4-mm diameter with a cork borer. Make three or four weUs per dish. Holes should be at least 1.5 cm apart. Place a sample of 8 pi in each well with a micropipette. Seal dishes with parafilm. Incubate at 30°C for 96-120 h. The higher the tannin concentrations, the longer it takes to reach equilibrium. The size of the diffusion rings will stabilize after about 5 nights. 

Plot the time spent on feeding as a function of tannin concentration. 

If more time (in terms of days) is available, study the effect of the tannin diets on the caterpillars How do the different tannin concentrations affect weight and survival of the animals (see Nomura and Itioka 2002). 

Figure 1 Comparative concentrations of tannins and alkaloids in fruits from three seed ecological groups. Data are the mean derived from all species examined. Tannin concentrations are in g g freeze dried weight, alkaloid concentrations are based on a semi-quantitative precipitation test.

The use of antipyrine as an agent for the concentration of tannin in tannin extracts has been proposed.66 Antipyrine forms a water-insoluble complex with tannin and the complex is easily decomposed by treating an aqueous suspension with organic solvents. These properties can be utilized for tannin concentration. 

This value may be somewhat distorted due to an increase in the wine s gallic acid and ellagic tannin concentration during aging in new barrels. The coefficients corresponding to these molecules are certainly very high, approximately 38. This increase only lasts a limited time, due to the rapid oxidative degradation of these compounds. 

Although this method is highly reproducible and easy to implement, it only gives an approximate result, as it does not take into account the effect of the various structures present in wine (Porter et al, 1968), nor their degree of polymerization, nor the other components in wine that interfere with the assay. The tannin concentration in wine is often overestimated. It is not unusual to observe an increase in the results of this assay during barrel and bottle aging, which may not correspond to an increase in tannin. 

On the basis of these observations. Glories (1988) developed two methods for calculating the tannin concentration in wine. The assay procedure (LA) is unchanged. 

The second method for calculating the tannin concentration is based on examining the visible spectrum of the reaction (LA). The following equations apply, whatever the degree of polymerization and concentration of the procyanidins. AOD 520, AOD 470 and AOD 570 represent the difference in OD, with or without heating, for the three corresponding wavelengths ... 

The results are compared with those of an oligomeric procyanidin solution derived from grape seeds and the tannin concentration is calculated using the following equation ... 

Tannin concentrations range from 1 to 4 g/1 in red wine and from 10 to 200 mg/1 in white wine. These values depend on the type of grapes, their degree of ripeness, the effects of rot (if any) and winemaking techniques. 

In addition to the tannin concentration of a wine, enologists also need information on the structures that govern the properties of the various compounds. Of course, the ideal solution would be to separate and assay the various molecular units included in the concept of tannin. Thanks to high-performance techniques, these analyses are now possible, although they are still difficult to implement. 

The procedure consists of adding 5 ml of cold-soluble gelatin solntion (70 g/1) to 50 ml of red wine. After three days, the wine is centrifuged and the tannins (LA) in the supernatant diluted to 1/50 are assayed to determine the tannin concentration Cl (g/1). Co is the tannin concentration of the control, prior to the addition of gelatin. The gelatin index is given by the equation ... 

Making objective measurements of these basic sensations is particularly complex. However, the gelatin index provides an estimate of reactivity to proteins. The intensity of the polyphenol-gelatin reaction depends on conditions in the medium. Acidity is a favorable factor, unlike alcohol content, which inhibits the reaction and gives a sweet taste. The reaction is independent of the tannin concentration at values above 50 mg/1 (Glories, 1983). Under given reaction conditions, it is thus possible to classify the various polyphenols according to their aptitude to combine. 

Fig. 6.39. Increase in the anthocyanin and tannin concentration in the skins and seeds as the grape ripens (Glories, 1986)...

The results in Table 10.2 show an excess of negative charges attributable to tannins and other compounds, such as polysaccharides (Tobiason and Hoff, 1989 Tobiason, 1992 Ferrarini et al., 1995 Vemhet et al., 1995). The surface charge density of red wines is neither proportional to the total phenols nor to the tannin concentration. The differences observed are probably due to grape varieties, the richness of the grapes (polysaccharides) and the wine s state of development. 

When a standard quantity of proteins is added, the quantity of tannins taken up generally increases with the tannin concentration of the wine, with certain exceptions. For example, Lagune (1994) showed that 5 g/hl of gelatin eliminated 120 mg/1 of tannin from a red wine that initially contained 1.72 g/1. Only 40 mg/1 was eliminated from another Bordeaux red wine with a much higher tannin content (3.54 g/1). 

In addition to the molecnlar strnctnre, the tan-nin/anthocyanin ratio also affects wine development. Color has been observed to change rapidly due to anthocyanin breakdown reactions when the medinm has a low tannin content (molar ratio T/A tannin polymerization reactions when the tannin concentration is much higher than the anthocyanin content (molar ratio T j A < 4). If a wine is to develop harmoniously, this ratio should be between 1 and 4, i.e. 500 mg of anthocyanins and 1-3 g of tannins per liter of wine. 

Tannin concentration reqnired to protect CEM cells against the cytopathogenicity of HIV by 50% (MIC)... 

Quantitation of total tannin concentration is still carried out by methods based on the classic Bate-Smith reaction heating in strong acid medium leads to the formation of carbocations, which in an oxidant medium forms cyanidin (an anthocyanin). The reaction mixture thus turns red (hence the old name... 

The low efficiencies of S. eridania on all tree leaves tested (see Fig. 7.5) may be the result of a variety of factors (e.g., low leaf water, low nitrogen, high fiber, high tannin concentrations). The growth rates on trees generally remain... 

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