AN OVERVIEW ON TANNINS

Abstract

This review was investigated and identification structure, role of the tannins in plants structure. Tannins are a complex group of polyphenolic compounds found in a wide range of plant species commonly consumed by ruminants. They are conventionally classified into two major groups: - the hydrolysable and the condensed tannins. During growth and maturation period in plants some substances can be found in structure of them which they have essential role in plant fortune. These substances are called plants secondary metabolites. One of the most important of secondary metabolites is Tannins. A great deal of research with tannins has followed an approach that looks at biological relationships: taxonomy, phylogeny, biosynthesis, nutritional and physiological effects on herbivorous animals e.g. ruminants. Their antimicrobial properties seemed to be associated with the hydrolysis of ester linkage between gallic acid and polyols hydrolyzed after ripening of many edible fruits. Tannins in these fruits serve as a natural defense mechanism against microbial infections. The antimicrobial property of tannic acid can also be used in food processing to increase the shelf-life of certain foods, such as catfish fillets. Tannins have also been reported to exert other physiological effects, such as to accelerate blood clotting, reduce blood pressure, decrease the serum lipid level, produce liver necrosis, and modulate immunoresponses. The dosage and kind of tannins are critical to these effects. The aim of this review is to summarize and analyze the vast and sometimes conflicting literature on tannins and to provide as accurately as possible the needed information for assessment of the overall effects of tannins.