Gallotannine

Simple phenolics and their derivatives (benzoic, gallic, ellagic, gallotannins and ellagitannins), flavonoids and condensed tannins... 

Niemetz R, Gross GG (2005), Enzymology of gallotannin and ellagitannin biosynthesis , Phytochemistry, 66, 2001-2011. 

The chromophores contained in natural dyes are mainly flavonoids, antrachinoids, indigoids and gallotannins. Other molecular types include carotenoids, benzochinons and anthocyanidins. 

The most widely used method is based on the reaction between potassium iodate and hydrolyzable tannins (Hartzfeld and others 2002). This method provides a good estimate for gallotannins but underestimates the content of ellagitannins. 

Other analytical assays proposed for the quantification of hydrolyzable tannins in plant materials include the rhodanine assay for the estimation of gallotannins (Berardini and others 2004) and sodium nitrate for the quantitative determination of ellagic acid (Wilson and Flagerman 1990). 

Berardini N, Carle R and Schieber A. 2004. Characterization of gallotannins and benzophenone derivatives from mango (Mangifera indica L. cv. Tommy Atkins ) peels, pulp and kernels by high-performance liquid chromatography/electrospray ionization mass spectrometry. Rapid Commun Mass Spectrom 18(19) 2208—2216. 

The separation characteristics of unmodified silica, diol, cyano, cellulose and RP-18 stationary phases were compared for the analysis of ellagitannins, gallotannins and flavonoid glycosides in the aerial parts of Erodium cicutarum (Geraniaceae) (stork s bill). Its decoction has been used in cases of dysentery, fever, wounds and worm infections. The air-dried and powdered plant material (300 g) was extracted three times with water-acetone (1 1, v/v) at ambient temperature. The collected extract was filtered and concentrated. The aqueous phase was acidified to pH 3 with formic acid and separated in an ODS column. Polphenols... 

Tannins derive their name from their ability to tan (i.e. they combine with protein). They render plants less palatable and impair digestion by binding with the buccal mucosa, dietaiy proteins, and digestive enzymes of the animal. Tannins are thought to bind to proteins upon destruction of plant tissue by herbivores. This reduces the nutritive value of the plant to the herbivore. Some tannins such as oak gallotannins, are even toxic to livestock and rabbits (Meyer and Karasov, 1991). However, Martin and Martin (1983) have questioned the role of tannins as plant defense against herbivores. 

Figure 1. Structure of a gallotannin typical of Chinese gallotannin, found, e.g., in galls of Rhus semialata. Note the characteristic meta-depside linkages of the galloyl residues at C-2.

In enzymatic studies with cell-free extracts from higher plants, however, no evidence has been found to date for galloyl-CoA s involvement in the biosynthesis of / -glucogallin, or its higher galloylated derivatives an eventual role in the formation of the chemically different meta-depside bonds of gallotannins has not been investigated. 

With respect to gallotannins, substantial evidence indicated that / -glucogallin was also metabolically active, as the acyl donor for galloyltrans-ferase reactions some details related to this aspect are described below. 

Little knowledge also exists on the mechanisms involved in the biosynthesis of the characteristic structures of gallotannins and ellagitannins, as will be briefly discussed below. 

Degradation of Gallotannins. Different investigations on tannase revealed that this enzyme was not equally efficient on all hydrolyzable tannins. This was particularly true for yeast, whose tannase was effective only on tannic... 

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