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The constituents of medicinal plants - Pengelly A.

Pengelly A. The constituents of medicinal plants - London, 2001. - 109 p.
Download (direct link): theconstituents2001.djvu
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Botanicals with condensed tannins include Eucalyptus spp, Hamamelis virginica, Cinchona spp., Acacia spp., and tea
(Camellia sinensis).
Astringent action
Astringents cause contraction of tissue, blanching and wrinkling of mucous membranes, and diminished exudations. When applied to wounds they form a thin protective surface, cutting down on secretion of exudates. Precipitation of proteins and/or polysaccharides on the surface results in hardening of the epidermis, reducing absorption of toxins, and protecting against irritants. Tannins display antimicrobial properties. Many are able to constrict blood vessels, thereby reducing bleeding.
Uses of tannins
1. Protecting inflammed mucous membranes
2. Drying effect on mucous membranes, reduces hypersecretions
3. Reduces inflammation and swelling which accompany infections
4. Prevents bleeding from small wounds
5. Reduce uterine bleeding eg. menorrhagia, metrorrhagia
6. Binding effect in the gut - relieves diarrhoea, dysentry.
7. Used externally as douches, snuffs, eyewash.
Some recent findings in research on tannins
1. Anti-viral activity against Herpes simplex in vitro. Anti-HIV activity [Okuda et al. 1989].
2. Antimicrobial. Catechin tannin extracts exhibited antibacterial activity against seven tested microorganisms (include. E.coli, Staph, aureus, Salmonella). The activity was lower than that of the reference drug tetracycline [Lutete et al. 1994]. Tannins also inhibit the growth of many filamentous fungi, though yeasts appear to be more resistant [Scalbert 1991].
3. Antioxidant properties. Inhibition of lipid peroxidation found to be strongest in ellagitannins followed by condensed tannins. Inhibits auto-oxidation of ascorbic acid (eg. geranium ellagitannin) [Okuda et al. 1988]. The proanthocyanidins or pycnogenols, condensed tannins derived from pine bark and grape seeds are potent antioxidants for the vascular system. Similar compounds are found in the hawthorne (Crataegus spp.).
4. Inhibition of gastric secretions - ellagic acid reduces occurrence of stress-induced gastric lesions, especially duodenal ulcers [Murakami et al. 1991].
5. Hepatoprotective - 46 tannin compounds from Chinese herbs were assessed employing experimentally induced cytotoxicity in primary cultured hepatocytes. Most tannins exhibited prominent effects in the CCL} induced toxicity. Of these the hydrolysable tannins were the most potent [Hikino 1985]. •*
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Phenolic compounds in foods
Anthocyanin pigments (condensed tannins) are found in red/blue/black fruits. Ribes, Rubus & Vaccinium fruits were shown to possess superoxide radical scavenging and antilipoperoxidant activities [Constantito et al. 1994].
Grape seeds are a major source of the condensed tannins known as oligomeric proanthocyanidins (OPCs) [Bombardelli & Morazzoni 19951.
Condensed tannins are also found in teas and red wine. Green tea is especially rich in the beneficial epigallocatechins [Wohlmuth 1995] while herb teas are generally low in tannins [Blake et al. 1993]. Chlorogenic acid is found in many fruits and vegetables, it is responsible for browning in apples and potatoes [Carper 1988]. Ascorbic acid may be added (eg. to apple juice) as an anti-oxidant to prevent browning.
Globe artichoke - Cynara scolymus (Asteraceae) contains the cinnamic acid depsides cynarin and chlorogenic acid.
Tannins as digestive inhibitors
Consumption of tannins may lead to reduced absorbtion of proteins and other nutrients. For this reason it is not considered wise to drink strong tea with meals. This can also lead to problems in compounding herbal medicines since there is a tendency to cause precipitates in some cases.
MISCELLANEOUS PHENOLIC COMPOUNDS
The basic phenolic structure occurs in many other classes of compounds found in medicinal herbs, including the following:
Glycosides eg. most flavonoids, anthraquinones Essential oils eg. thymol Alkaloids eg. oxyacanthine Sterols
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References
Adzek. T. & Camarasa, J. 1988. Pharmacokinetics of polyphenolic compounds. In Herbs, Spices & Medicinal Plants VoL3. Oryx Press, Phoenix USA.
Ammon, H. & Wahl, M. 1990. Pharmacology of Curcuma longa. Planta Medica 57:1-7.
Beckham, N. 1995. Phyto-oestrogens and compounds that affect oestrogen metabolism - Pt.l Aust.J. Med. Herbalism 7:11-16.
Bombardelli, E. & Morazzoni, P. 1995. Vitis vinifera L. Fitoterapia LXVI: 291-317.
Blake, 0.1993/94. The tannin content of herbal teas. BrJ Phytotherapy 3: 124-127.
Bruneton, J. 1995. Pharmacognosy Phytochemistry Medicinal Plants. Lavoisier Pubs, Paris.
Cadenas, E. & Hochstein, P. 1992. Pro- and antioxidant functions of quinones and quinone reductases in mammalian cells. Advances in Enzymology 65:97-146.
Carper, J. 1988. The Food Pharmacy. Bantam Books, New York
Constantino L. et al. 1994. Composition, superoxide radicals scavenging and antilipoperoxidant activity of some edible fruits. Fitoterapia LXV: 44-47.
Dorsch, W. 1994. Antiasthmatic acetophenones - an in vivo study on structure activity relationship. Phytomedicine 1: 47-54.
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