Tannins changes

The apphcation of vegetable tanning materials has an additive effect on the leather. The more vegetable tannins appHed the more the leather becomes like vegetable-tanned leather. The color is changed, the fullness of feel increases, and the leather can be worked and embossed like vegetable leather. 

A study of the effect on the congener levels of up to eight refills of a used whiskey barrel iadicate that volatile acids, esters, colors, soHds, and tannins showed the greatest percentage change between the first and second use of a new charred barrel (11). 

The natural moisture of the cocoa bean combined with the heat of roasting cause many chemical reactions other than flavor changes. Some of these reactions remove unpleasant volatile acids and astringent compounds, partially break down sugars, modify tannins and other nonvolatile compounds with a reduction in bitterness, and convert proteins to amino acids that react with sugars to form flavor compounds, particularly pyrazines (4). To date, over 300 different compounds, many of them formed during roasting, have been identified in the chocolate flavor (5). 

Tea Beverages. Uncoated aluminum is not compatible with tea beverages since direct contact causes discoloration and undesired flavor changes during storage. When the water contains dissolved iron, it can react with the tannin in the tea and cause darkening in the presence of air. Dissolved air in the beverage or in the headspace of the can should be... 

The members of this class dye wool and silk directly, but cotton only when the latter is mordanted by tannin. They are fast neither to acids nor to alkalis for reasons which depend on important alterations in the compounds. If a little dilute hydrochloric acid is added to an aqueous solution of crystal violet the colour changes to green. One N(CH3)2-group takes part in the change and there is formed the salt with two equivalents of acid ... 

As documented in a review article (9), no experimental data was available to support hypothetical mechanisms for the biosynthesis of hydrolyzable tannins until recently. Enzymatic studies have now changed this unsatisfactory situation, at least as far as the formation of pentagalloylglucose is concerned. Future work will provide insight into those other challenges discussed in this contribution and that still require clarification. 

Nishioka. Tannins and related compounds. CXIV. Structure of novel fermentation products, theogallinin, theaflavonin and desgalloyl thea-flavonin from black tea and changes of tea leaf polyphenols during fermentation. Chem Pharm Bull 1992 40(6) 1383-1389. 

Bavage, A.D. et al.. Expression of an Antirrhinum dihydroflavonol reductase gene results in changes in condensed tannin structure and accumulation in root cultures of Lotus corniculatus (bird s foot trefoil). Plant Mol Biol, 35, 443, 1997. 

Again, one pound of galls is exhausted as first directed, and the tannin of the decoction changed, by exposure, into gallic acid, as in the last instance. The menstruum is then mixed with a saturated solution of logwood, freshly made by boiling a pound and a half of the chips in five quarts of water, till the quantity is reduced to seven pints eighteen ounces of sulphate of iron, and as many of gum, are dissolved in this mixed liquid the whole is allowed to stand for two or three days, and the ink is then, decanted from the sediment. 

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