Antioxidant activity of tannins

Oxidative cellular damage by reactive oxygen species such as superoxide anion, hydroperoxy and hyassociated with various human chronic diseases, e.g. cancers, inflammation, arthritis, atherosclerosis and also with the process of ageing. Claims that diet and increased intake of nutrients exhibiting antioxidative activity have a preventative effect on chronic diseases have increased in recent years. In this context, polyphenolic compounds such as tannins, flavonoids, coumarins, lignans and caffeic acid derivatives, which are abundantly contained in a large number of medicinal plants, foods and beverages, are of particular interest for human health care because of the antioxidative properties widely found in plant phenolics. The antioxidative activity of tannins has been extensively studied in various in vitro and in vivo experimental systems and summarized in reviews [96, 97]. Such activity includes the inhibition of lipid peroxidation induced by NADPH-ADP and ascorbic acid-ADP in rat liver microsomes and mitochondria, respectively... 

Ho KY, Huang JS, Tsai CC, Lin TC, Hsu YF, Lin CC (1999) Antioxidant activity of tannin components from vaccinium vitis-idaea L. J Pharm Pharmacol 51 1075-1078... 

Antioxidant Activity of Tannins and Tannin-Protein Complexes Assessment In Vitro and In Vivo... 

Siwela, M., Taylor, J. R. N., de Milliano, W. A. J., and Duodu, K. G. (2007). Occurrence and location of tannins in finger millet grain and antioxidant activity of different grain types. Cereal Chem. 84,169-174. 

Pomegranate juice was shown to possess an antioxidant activity that was three times higher than the antioxidant activity of green tea.19 The antioxidant activity was higher in juice extracted from whole pomegranate than in juice obtained from arils only, suggesting that the processing extracts some of the hydrolyzable tannins present in the fruit rind into the juice. 

With respect to the activity of tannins, Momose et al. [157] have demonstrated that gallic acid exhibits higher activity than the tannins derived from it. Gallic acid was found to induce apoptosis in different cell lines this induced cell death was mediated by ROS such as hydrogen peroxide and superoxide anion, as well as by Ca2+. However, the induction of apoptosis depends on the acid s distinctive structural features rather than on its antioxidative activity [158]. In fact, the... 

Plant foods contain a number of bioactive substances, including phenoUcs. Phenolics such as flavonoids, phenolic acids, lignans and tannins have antioxidant properties, whilst the fermentation process has been d onstrated to modify the amount of these contents. l,l-Diphenyl-2-picryldrazyl (DPPH) and 2,2 -azinobis-(3-ethylbenzothi-azoline-6-sutfonic acid) (ABTS) are tests commonly used to detennine the free radical-scavenging effectiveness of componnds in evaluating the antioxidant activity of food systems. 

Seeram NP, Adams LS, Henning SM, Niu Y, Zhang Y, Nair MG, Heber D (2005) In vitro antiproliferative, apoptotic and antioxidant activities of punicalagin, ellagic acid and a total pomegranate tannin extract are enhanced in combination with other polyphenols as found in pomegranate juice. J Nutr Biochem 16 360-367... 

The antioxidant activities of phenolic natural products have been recognized for some time. However, an understanding of the contribution diat dietary polyphenolic compounds might make to human health has not been achieved. Tannins comprise a significant fraction of the natural products consumed in the human diet, with an estimated intake of more than one g per day (8). Thus the potential contribution of these compounds to physiological antioxidant capabilities is substantial. 

In previous studies, we investigated the antioxidant activity of various compound chosen from Oriental medicine, paying particular attention to the correlation between molecular structure and activity. We have found that tannin and phenol compounds such as flavones possess such activity, and that tea, which contains these compounds as its major components, has high antioxidant activity (1,2). 

Amarowicz, R., Naczk, M. and Shahidi, F. 2000. Antioxidant activity of various fractions of non-tannin phenolics of canola huUs. J. Agric. Food Chem. 48 2755-2759. 

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. 

Extracts of V. africana are used to treat AIDS. Phytochemical screening revealed the presence of important antioxidant bioactive molecules such as tannins, flavonoids and phenols in bark extracts (S). They concluded that the antioxidant activity in this medicinal plant may be a contributing factor to its therapeuctic applications. Additional medicinal applications of Voacanga have been reviewed in relation to other African medicinal plants 3, 70). 

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