Of tannin

C7H6O4. Crystallizes with IH2O m.p. 199" C. It occurs in the free state in the onion and other plants is a constituent of one group of tannins, and is a product of the alkaline decomposition of resins. 

The quahty of individual gums is mainly deterrnined by color and taste or odor. Many gums are colorless when secreted, but darken on aging. Most gums are usually tasteless unless contaminated by the bitter flavors of tannins which precludes their use in foods. 

Plants and microorganisms produce unique and diverse chemical stmctures, some of which act as immunomodulators (18—28). Of specimens used in traditional medicine, approximately 450 plant species have shown antiviral activity out of 4000 plants screened (19). Several tannins (20) exhibit strong inhibition of tumor promotion experimentally. Pretreatment of mice with small amounts of tannins for several days strongly rejected transplanted tumors. This activity has been claimed to be effected through enhancement of host-mediated antitumor activity. 

Niobic Acid. Niobic acid, Nb20 XH2O, includes all hydrated forms of niobium pentoxide, where the degree of hydration depends on the method of preparation, age, etc. It is a white insoluble precipitate formed by acid hydrolysis of niobates that are prepared by alkaH pyrosulfate, carbonate, or hydroxide fusion base hydrolysis of niobium fluoride solutions or aqueous hydrolysis of chlorides or bromides. When it is formed in the presence of tannin, a volurninous red complex forms. Freshly precipitated niobic acid usually is coUoidal and is peptized by water washing, thus it is difficult to free from traces of electrolyte. Its properties vary with age and reactivity is noticeably diminished on standing for even a few days. It is soluble in concentrated hydrochloric and sulfuric acids but is reprecipitated on dilution and boiling and can be complexed when it is freshly made with oxaHc or tartaric acid. It is soluble in hydrofluoric acid of any concentration. 

Tannins occur in many plants and are separated by extraction. At present, only quebracho extract is used as a mud thinner in significant quantity in the United States. Quebracho is an acidic material and performs best at high pH. It is an excellent thinner for lime-treated and cement-contaminated muds. However, it is not effective at high salt concentrations. Sulfomethylated tannin products are functional over a wide range of pH and salinity and have either been treated with chromium for good thermal stabiUty (58) or are chrome free. Concentrations of tannin additives are ca 1.5—18 kg/m (0.5—6 lb/bbl). 

In wooden tubs, the maintenance of a sanitizer residual becomes compHcated due to the leaching of tannins and other organic matter from the wood into the water. The sanitizer demand of these substances must be overcome in order to maintain proper residual concentrations. As the tub ages, the leaching of these materials decreases, but bleaching of the wood may occur as the lignin (qv) in the wood reacts with sanitizers. 

Upon mashing, small amounts of tannin go into the solution from the malt, and later, during the boiling with hops, more tannin goes into the wort. Tannins from both barley and hops are leucoanthocyanin stmctures, in some cases they are derivatives of quercetin [117-39-5], cathechins are not found. The turbidities in beer, rich in leucoanthocyanins, are composed of peptones, peptides, and condensation products of the tannins of malts and hops. 

Maturing improves the taste and aroma of beer and the elimination of tannin, protein, and hop resins also has a beneficial effect. Some metaboHc products of unpleasant taste are further converted or washed out by the carbon dioxide surplus. The time for 1 agering varies with different types of beer. For every type of beer there is an optimal 1 agering time, and longer ] agering is usually detrimental to beer quaHty. The fiHed 1 agering tanks are subjected to the saturating pressure of carbon dioxide, usually 50—70 kPa (ca 0.5—0.7 atm), controUed by a safety valve. 

Besides the medicinally used herbal mixtures, there arc also the so-called household teas which are preferred by people who are sensitive to coffee or who do not wish to drink a caffeine-containing beverage on a regular basis. Household teas are made up from drugs which, apart from small amounts of tannins, have only aroma substances and possibly also plant acids bramble leaves, raspberry leaves, hibiscus flowers, hips and haws, and apple skins arc frequent components of such teas [4]. 

The autocatalytic hardening of tannins without addition of formaldehyde or another aldehyde as crosslinker is possible, if small traces of alkaline Si02 are present as catalyst and also a high pH is used, or with certain tannins just by the catalytic action induced by the wood surface [152-160]. 

Either straightforward drainage or blowdown can readily remove sludge from the plant. It is, however, necessary in some cases to ensure that the residual solids are free-flowing this is achieved by the use of tannin, lignin, seaweed derivatives, and starch organics. 

V sol in ethanol v si sol in acet acid. Prepn is by prolonged heating of tannin with a 5% aq sulfuric acid soln. It is also a coprod of the hydrogenation of tetraacetyl-2-oxy-glucal (Ger) with a Pd catalyst followed by saponification with Ba hydroxide... 

NOTE The British Standards Institution provided only a cursory mention of tannins in BS 2486 1978 (Treatment of Water for Land Boilers), but the 1997 revision (Treatment of Water for Steam Boilers and Water Heaters) refers quite extensively to tannins and their usefulness. 

Although tannins are almost always formulated as a blend of raw materials, some knowledge of tannin chemistry is required because certain tannin constituents are useless in BW formulations and others lack... 

Pyrogallol, another oxygen scavenger (and a reaction product of tannins), often is used as a catalyst for HQ. 

Alkalinity boost chemistries typically are based on adjunct products containing primarily potassium hydroxide (for maximum solubility) or sodium hydroxide (for lowest cost), although sodium carbonate is still used in certain limited applications. These adjuncts may also contain (in almost any combination) smaller percentages of tannins, sodium ligonsulfonate, phosphate or polymers. 

Because of thermal decomposition, the use of tannin above 20 bar (290 psig) or isoascorbic acid above 60 bar (870 psig) is not recommended. 

The allelochemistry of the two forests also shows striking differences. Analyses showed that the Douala-Edea site has a higher proportion of tannin-producing taxa, whereas species at the Kibale site exhibited a much higher frequency of alkaloid... 

Some of the best investigated anti-nutrients are the enzyme inhibitors present in legumes and other plants. The Bowman-Birk and the Kunitz inhibitors of trypsin and other proteases are among the best characterized. In contrast to the non-specific and widespread influences of tannins and lectins (Carmona, 1996), the Bowman-Birk, Kunitz and other such inhibitors target specific enzymes. Corresponding with this, proteases and other digestive enzymes vary in sensitivity to the different inhibitors. 

REED J D (1995) Nutritional toxicology of tannins and related polyphenols in forage legumes. JAnim Sci. 73 1516-28. 

Other aquatic weeds such as reed mat, mangrove (leaves), and water lily (Nymphaceae family plants) have been found to be promising biosorbents for chromium removal. The highest Cr(III) adsorption capacity was exhibited by reed mat (7.18 mg/g), whereas for Cr(VI), mangrove leaves showed maximum removal capacity (8.87 mg/g) followed by water lily (8.44 mg/g). It is interesting to mention that Cr(VI) was reduced to Cr(III), with the help of tannin, phenolic compounds, and other functional groups on the biosorbent, and subsequently adsorbed. Unlike the results discussed previously for the use of acidic treatments, in this case, such treatments significantly increased the Cr(VI) removal capacity of the biosorbents, whereas the alkali treatment reduced it.118... 

The tannins are synthesized by plants and are abundantly distributed in many different forms of plant life. Common sources of tannins include for example, the bark, leaves, fruit and roots of many plants most tannins, however, have been and are still derived from the bark of a few trees and shrubs, such as oak, chestnut, hemlock, mangrove, quebracho, and wattle, from which they are generally extracted with water. 

Aronson, J. L., T. J. Schitt, R. C. Walter, M. Taieb, J. J. Tiercelin, D. C. Johnson, C. W. Naeser, and A. E. M. Naim (1976), New geochronologic and palaeomagnetic data from the hominid bearing hadar formation of Ethiopia, Nature Hoi, 323-327. Arpino, P, J. P. Moreau, C. Oruezabal, and E. Flieder (1977), Gas chromatographic-mass spectrometric analysis of tannin hydrolysates from the ink of ancient manuscripts (XI to XVI centuries), /. Chromatogr. 134, 433-439. 

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