Tannins chemical properties

The strongly astringent taste of persimmon fruits arises from soluble tannins that accumulate in large specialized cells called tannin cells. In this chapter, some chemical properties of persimmon tannins, an outline of simple and reliable methods for estimation of the degree of astringency and the amount of tannins, and some aspects of the physiological changes in the tannin contents of persimmon fruits will be described. 

The basic structure of persimmon tannin seems to be, as proposed by Matsuo and Ito (1977b, 1978), a proanthocyanidin polymer. Some differences in the constituents and chemical properties of persimmon tannin among the four fruit types as classified in terms of astringency have been reported. Nakabayashi (1971) foimd three patterns of low-molecular-weight polyphenols (one in PCNA fruit, one in PVNA fruit and one in PVA and PCA fruit) the components were different. Yonemori et al. (1983) reported differences observed in the amounts of catechin and gallic acid in tannins extracted from immature PCNA fruit and the immature fruit of the three other types. 

The differences in the chemical properties of persimmon tannins between immature PCNA fruit of the cultivar Fuyu and immature PVA fruit of the cultivar Hiratanenashi were further investigated by exclusion chromatography (Yonemori and Matsushima 1984). Tannins from the former cultivar were generally of lower molecular weight than those from the latter (Fig. 2). Fuyu tannins tended to coagulate more slowly in the presence of acetaldehyde vapour than those from Hiratanenashi, indicating that polymerization occurred less readily. 

All the tannins readily react with proteins, forming insoluble, stable compounds when they react with collagen, the main constituent of animal skin, they form leather, a material that is resistant to hydrolysis, oxidation, and biological attack and therefore stable to weathering and resistant to decomposition. Since tannins from different plant sources have different chemical compositions, each tannin used for tanning skin produces a leather having slightly different properties and color. Tannins that have... 

Contradictory opinions have been referred to in the literature particularly on the nature of the iron-tarmate and its interaction with the rusted steel due to the diversity of the material used in different studies. Studies have included the use of tannic acid [7-10], gallic acid [11], oak tannin [12, 13], pine tannin [14] and mimosa tannin [15]. In order to establish the correlation between the ferric-taimate formation and the low inhibition efficiency observed at high pH from the electrochemical studies, phase transformations of pre-rusted steels in the presence of tannins were evaluated. In this work the quantum chemical calculations are conducted to analyse the relationship between the molecular stracture and properties of ferric-taimate complex and its inhibitory mechanism. 

Abstract Recently, the interest on biomaterials and especially in tannins was growing and some attractive results were obtained in the adsorption of some metals by tannin adsorbents. Tannins are widely distributed in nature and have multiple adjacent polyhydroxyphenyl groups in their chemical structure which have extremely high afiSnity for heavy metal ions. This study will describe how tannin can be used as an effective zinc and lead sorbent by the use of tannin resins. Batch method was used in the experiments in which pH profde, adsorption time, adsorbent/liquid ratios, initial concentration of metal ions, adsorbent amount and temperature were investigated to determine binding properties of adsorbent for the Zn(II) and Pb(ll) ions. 

In some cases, browsing does not appear to lead to induced defenses. Two species of northern European birch (B. pendula and B. pubescens) do not seem to respond to moose browsing with increased chemical defenses (Danell et ah, 1985). After experimental defoliation, the Emory oak of southwestern North America, Quercus emoryi, produces in its regrown leaves 2.5 times as much hydrolyzable tannins than in mature leaves, but lower amounts of condensed tannins. Refoliated branches suffered more, not less herbivory. New leaves have more protein, more water, and are tender. These properties may override any effects of induced chemical defenses, at least for the current growing season (Eaeth, 1992), but the induced compounds may still protect a plant later on, especially in winter. 

It would seem more realistic to define as tannins all naturally occurring substances which have chemical and physical properties akin to those... 

Comfrey (Symphytum officinale) Uses Topical treatment of wounds, bruises, sprains, inflammation Action Multiple chemical components, allantoin promotes cell division, rosmarinic acid has anti-inflammatory effects, tannin possesses astringent effects, mucilage is a demulcent w/ anti-inflammatory properties, pyrrolizidine alkaloids cause hepatotox Available forms Topical application w/ 5—20% of herb applied on intact skin for up to 10 d Contra Do not take orally d/t hepatotox, do not use if PRG or w/ lactation Notes/SE N/V, exfoliative dermatitis w/ topical use Interactions T Risk of hepatotox W/ ingestion of borage, golden ragwort, hemp, Petasites EMS None... 

Tannins are used in medicine primarily because of their astringent properties, which are due to the fact that they react with the proteins of the layers of tissue with which they come into contact. Tannins are known to tan the outermost layer of the mucosa and to render it less permeable and more resistant to chemical and mechanical injury or irritation however, the correlation between the molecular structures of tannins and the astringent/antiulcer activity is not known. 

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