Tannins hydrolysable

Amao MB, Cano A, Alcolea JF and Acosta M. 2001b. Identification of hydrolysable tannins in the reaction zone of Eucalyptus nitens wood by high performance liquid chromatography-electrospray ionisation mass spectrometry. Phytochem Anal 12(2) 120—127. 

Two different types of tannin, condensed and hydrolysable tannins, play important roles. 

The second group of tannins are the condensed tannins, or polymeric proanthocyanidins (2). These are composed offlavonoid units, and are more recalcitrant to biodegradation than hydrolysable tannins. Of these, the... 

In 1913, Knudson (17) reported that tannic acid (the commercial name of the Chinese gall tannin) could be degraded by a strain of Aspergillus niger previously the French scientist Pottevin (in 1900) had named this enzyme tannase (10). Since then, most of the progress on elucidating the mechanisms of hydrolysable tannin biodegradation has occurred since 1960. 

Hydrolysable tannins and proantho-cyanidins from green tea. Phytochemistry 1984 23(8) 1753-1755. 

Tannins can be classihed into two major classes hydrolysable tannins and condensed tannins. On treatment with acids or enzymes, while hydrolysable tannins are split into simpler molecules, condensed tannins produce complex water-insoluble products. 

Condensed tannins (= proanthocyanidins) unlike hydrolysable tannins, condensed tannins are polymeric flavans that are not readily hydrolysable. They often consist of molecules of catechin and epicatechin joined by carbon-carbon bonds. Hence catechin and epicatechin are referred to as monomers oligomers containing 2-4 (epi)catechin units are referred to as oligomeric procyanidins (OPC). 

The phenolics include anthocyanins, anthraquinones, benzofurans, chromones, chromenes, coumarins, flavonoids, isoflavonoids, lignans, phenolic acids, phenylpropanoids, quinones, stilbenes and xanthones. Some phenolics can be very complex in structure through additional substitution or polymerization of simpler entities. Thus xanthones can be prenylated and flavonoids, lignans and other phenolics can be glycosylated. Condensed tannins involve the polymerization of procyaninidin or prodelphinidin monomers and hydrolysable tannins involve gallic acid residues esterified with monosaccharides. As detailed in this review, representatives of some major classes of plant-derived phenolics are potent protein kinase inhibitors. 

Mueller-Harvey, I. 2001. Analysis of hydrolysable tannins. Anim. Feed Sci. Technol. 91 3-20. 

Good quality gallic acid may be obtained by hydrolysing tannin with 40% caustic soda solution at 70° with the addition of a little sodium bisulphite to protect the acid from oxidation. The gallic acid is then precipitated by cone, hydrochloric acid and crystallised from water. (Note.—Sulphuric acid must not be used.)... 

Tannins 1. hydrolysable tannins 2. condensed tannins Sumac (Rhus Sp.) oak (Quercus sp.) chestnut (Castanea sp.) alder (alnus sp.) Pineaceae family such as pine, spruce, hemlock Also called 1. gallotannins because they from esters with gallic acid 2. hydrated flavonols or proanthocyanidins Historically labeled as tanning agents... 

Tannins can be classified in three groups condensed tannins, hydrolysable tannins, and complex tannins (Khanbabaee and Van Ree, 2001). These groups can then be further divided, as shown in Figure 1-3. 

Gallotannins are hydrolysable tannins with a polyol core (referring to a compound with multiple hydroxyl groups) substituted with 10-12 gallic acid residues. Gallotannins contain the characteristic raeto-depside bonds (1.91) between gallic acid residues. This bond is more labile than an aliphatic ester bond, and can be methanolyzed with a weak acid in methanol. In contrast, methanolysis of an aliphatic ester bond requires methanol with a strong mineral acid and heat. 

Scalbert et al. (1989) described several methods to determine the concentration of hydrolysable and condensed tannins (proanthocyanidins see Chapter 1, section 3.13.1) in wood extracts. Tannins are complex and heterogeneous In addition to the distinction between the flavonoid-based condensed tannins and the gallic acid-based hydrolysable tannins, each group can display a large degree of chemical variability that can affect the efficacy of the different assays. Interference of chemically related nontannin compounds, such as flavonoids, can in certain cases bias the results. 

Gallotannins are hydrolysable tannins and contain a gallic acid residue esterified to a polyol (see Chapter 1, section 3.13.2). 

The contents of the ampule are diluted in water to a final volume of 50 mL. A 1-mL sample is then taken for the assay. To this sample 1.5 mL 0.667% (w/v) rhodanine in methanol is added. After exactly 5 min. 1 mL 0.5N KOH is added. After 2.5 min. water is added to a final volume of 25 mL. The absorbance is read at 520 nm after a 5-10 min. incubation. A standard curve is made by reaction of gallic acid in 0.2N sulfuric acid with the rhodanine solution. Hagerman and Butler (1989) argued that this assay is more suitable than the potassium iodate assay for the determination of hydrolysable tannins, although it has to be kept in mind that the rhodanine assay is sensitive to any gallic acid ester, including those in non-tannin compounds. 

Amariin (hydrolysable tannin) Phyllanthus amarus (Euphorbiaceae) HIV-1 protease (< 53 pM) [42]... 

Epicatechin 3-O-gallate (hydrolysable tannin) Widespread Rheum palmatum (Polygon aceae) ACE (80 pM) [81]... 

Gallic acid (= 3,4,5-Trihydroxybenzoic acid) (phenolic acid) Widespread basic constituent of the hydrolysable tannins (gallotannins) Mangifera indica (Anacardiaceae) PEP (487 pM) [115]... 

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