Tannins characteristics

Fig. 3. The regular structure of a procyanidin-type condensed tannin showing characteristic 4,8 interflavonoid bonds linking the flavonoid units.

Tannins make excellent BW inhibitors. They are multifunctional, possessing several characteristics that make them entirely suitable for the treatment of HW heating and LP steam boilers. They also are generally suitable for use in industrial and process WT boilers at pressures of up to 650 or even 950 psig. 

The classic seed burial studies of W. J. Beal and his successors have shown seeds of at least one weed species, Moth Mullein (Verbascum blattaria L.) can remain viable in soil for a peiod of 100 years, whereas three species continued to germinate after 80 years of burial (30). Weed seeds not only resist decay by soil microbes, but they vary in dormancy characteristics. There is considerable evidence that chemical inhibitors are responsible for both phenomena. Unsaturated lactones and phenolic compounds in particular, are potent antimicrobial compounds present in many seeds (4J. Fruits and seeds are also known to contain diverse germination inhibitors including phenolic compounds, flavonoids and/or their glycosides and tannins. Unique methods to destroy inhibitors could provide an excellent weed management strategy. 

Trihydroxybenzene carboxylic acid esters with a sugar are characteristic of hydrolyzable tannins .37 These, too, may be present in coffee... 

Hematein and hematoxylin are known as the main components of logwood, but other characteristic colourants are also present in its preparations, e.g. tannins and... 

Food and plant phenolics are commonly detected using DAD detectors (Tan and others 2008). Photodiode array detection allows collection of the entire UV spectrum during the elution of a chromatographic peak, which makes it possible to identify a phenolic compound by its spectra. Simple phenols, phenolic acids, flavanones, benzophenones, isoflavones, and flavan-3-ols have maximum absorbance at 280 nm, hydroxycinnamic acids at 320 nm, flavonols, flavones, and dihydroflavonols at 365 nm, and anthocyanins at 520 nm (Ibern-G6mez and others 2002 Merken Hand Beecher 2000). Hydrolyzable tannins show a characteristic shoulder at 300 nm, suitable for identifying them (Arapitsas and others 2007). For stilbenes, maximum absorbance of trans-forms are at 306 nm and at 285 nm for cA-forms (Lamuela-Raventos and others 1995). 

The tannins are special phenolic compounds characterized by their ability to combine with proteins and other polymers such as polysaccharides. This characteristic explains their tanning properties as arising from a tannin-collagen matrix and then astringency caused by precipitation of the proteins and glycoproteins from saliva. Also tannins are used in fining wines because they combine with proteins. Finally, they inhibit enzymes by combining with their protein fraction. 

Thus one arrives at a valid definition of tannins for plant chemistry, insofar as their characteristic properties are concerned, without reference to the leather industry. Such a definition has been given by Swain and Bate-Smith (28) ... 

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