Polyphenols—tannins and flavonoids

Yoshida, T., Mori, K., Hatano, T., Okumura, T., Uehara, I., Komogoe, K., Fujita, Y., and Okuda, T. 1989. Studies on inhibition mechanism of autoxidation by tannins and flavonoids. V. Radical-scavenging effects of tannins and related polyphenols on l,l-diphenyl-2-picrylhydrazyl radical. Chem. Pharmacol. Bull. 37(7) 1919—1921. 

The leaves of Catha edulis also have a high content of polyphenolic compounds, tannins and flavonoids. The isolated flavonic fraction showed a significant antiulcer activity against the lesions induced by phenylbutazone and pyloric ligature in rats [91]. It is proven that the compounds responsible for this activity are the major constituents of the... 

Hippophae rhamnoides L. Sha Ji (Sea buckthorn) (seed, fruit, leaf) Cryptoxanthin, harman, harmol, hemin, isorhamnetin, lycopene, serotonin, isorhamnetin-3-mono-beta-D-glucoside, polyphenols, fatty acids flavonoid, essential oils, tannins, quercitin, vitamin C, vitamin E, beta-carotenoid.50-450 Improve resistance to infection, skin irritation and eruption, treat heart disease, oil for cosmetic use. 

Both marketers of manufactured superfruit products and the public media have exaggerated the potential antioxidant importance of fruit compounds such as polyphenol pigments (anthocyanins, flavonoids, tannins, catechins, xanthones, and many others). These compounds have antioxidant activity in controlled laboratory conditions, but there is no scientifically confirmed evidence that they have antioxidant roles in the human body. 

Carica papaya L. [umphopho, pawpaw] (Caricaceae) leaf infusion is used for dysentery. The leaf contains flavonoids, glycosides, polyphenols, steroids and tannins (75). 

Gnidia kraussiana Meisn. var. kraussiana [umsilawengwe, yellow heads] (Thymelaeaceae) root decoction is for stomachache. Roots eontain anthranoids, flavonoids, polyphenols, saponins and tannins (15). The root is also used for remedies for bums and snakebites (28). 

Helichrysum odoratissimum (L.) Sweet [imphepho yentsaba, everlasting plant] (Asteraceae) leaf infusion is nsed for eonstipation (18). Yonng branches are used for conjunctivitis (33). The leaf eontains alkaloids, polyphenols steroids and tannins (18). The flowers eontain flavonoids and a ehaleone (34). 

Sclerocarya birrea (A. Rich.) Hochst. subsp. cafffra [umganu, marula tree] (Sond.) Kokwaro (Anacardiaceae) stem bark decoction is used for diarrhoea. The stem bark contains alkaloids, flavonoids, glycosides, polyphenols, steroids and tannins 15). Its antidiarrhoeic activity is due to the tannin content 37). The plant is also used for childhood convulsion and epilepsy, and its anticonvulsant activity has been demonstrated in experimental animal model (58). 

Scilla nervosa [ndwendwendwe, wild squill] (Burch.) Jessop. (Hyacinthaceae) bulb decoction is nsed for lower abdominal pains in women (26). The bulb contains alkaloids, cardenohdes, flavonoids, polyphenols, saponins, tannins and terpenoids (18). The bulb is also mixed with the roots of Crossandra fruticulosa Lindau [likhambilebantfwana, shade crossandra] (Acanthaceae) and then together used in treating peptic ulcers in children (12). 

Plants - Lignin, tannins, and pigments, flavor components of spices (cinnamon oil, wintergreen oil, bitter almond, nutmeg, cayenne pepper, vanilla bean, clove, and ginger) are derived from coniferyl alcohol. Coniferyl alcohol, in turn, is derived from phenylalanine and tyrosine. Phenylalanine is also a precursor of plant pigments and related polyphenolic compounds called flavonoids. The biosynthetic scheme leads to a class of flavonoids called anthocyanins, which are common flower pigments.. An offshoot of this pathway leads to the synthesis of cocaine. 

Among the polyphenols present in the tree barks, tannins are by far the most interesting oligomers (molecular weights of 1000-4000) in terms of their utilization as macromonomers for the crosslinking of proteins in leather (tanning) and for macromolecular syntheses. The two representative structures of the flavonoid units in tannins are shown in Fig. 1.8. The most salient aspects related to the sources, structures and production of tannins and to their exploitation in polymer modification and manufacture are given in Chapter 8. 

Tannins are considered polyphenols due to the large number of phenolic rings in their structures (Mosiewicki et al., 2007 Moubarik et al., 2009). These natural products can be found in certain plant tissues, such as bark, fruit and wood, and can be removed from these sourees by extraction with water. Tannins are classified in two groups hydrolyzable tannins and condensed tannins (Mueller-Harvey, 2001). The condensed tannins are flavonoids with complex structures (Fig. 2.5). The phenolic groups present in tannin enable this macromolecule to participate in the same reactions as phenol (Tondi and Pizzi, 2009). Condensed tannins are more suitable than the hydrolyzable type for use in the manufacture of a phenolic-type polymeric matrix due to the presence of phenolic rings with a greater number of free positions where the electrophilic attack can occur (Barbosa et al., 2010). The high reactivity of... 

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