Content uploaded by Akhilesh Tiwari
Author content
All content in this area was uploaded by Akhilesh Tiwari on Feb 23, 2021
Content may be subject to copyright.
A preview of the PDF is not available
AN OVERVIEW ON TANNINS Short Review
Abstract and Figures
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.
Figures - uploaded by Akhilesh Tiwari
Author content
All figure content in this area was uploaded by Akhilesh Tiwari
Content may be subject to copyright.
ResearchGate has not been able to resolve any citations for this publication.
Regular, moderate consumption of red wine is linked to a reduced risk of coronary heart disease and to lower overall mortality, but the relative contribution of wine's alcohol and polyphenol components to these effects is unclear. Here we identify procyanidins as the principal vasoactive polyphenols in red wine and show that they are present at higher concentrations in wines from areas of southwestern France and Sardinia, where traditional production methods ensure that these compounds are efficiently extracted during vinification. These regions also happen to be associated with increased longevity in the population.
Tannin acyl hydrolase (Tannase) from Asp. oryzae No. 7 was purified. The purified enzyme was homogenous on column chromatography (DEAE-Sephadex A50, Sephadex G100), ultra centrifugation and electrophoresis. The molecular weight of the enzyme estimated by gel filtration method was about 200,000. The enzyme was stable in the range of pH 3 to 7.5 for 12 hr at 5°C, and for 25 hr at the same temperature in the range of pH 4.5 to 6. The optimum pH for the reaction was 5.5. It was stable under 30°C (over one day, in 0.05 M-citrate buffer of pH 5.5), and the optimum temperature was 30˜40°C (reaction for 20min). The activity was lost completely at 55°C in 20 min at pH 5.5, or at 85°C in 10 min at the same pH. Any metal salt tested did not activate the enzyme, Zink chloride and cupric chloride inhibited the activity or denatured the enzyme. The activity was lost completely by dialysis against EDTA-solution at pH 7.25, although it was not affected by dialysis against deionized water.
Two procyanidin tetramers, two trimers, and a dimer which is a structural isomer of procyanidin B-1, along with (+)-catechin, (–)-epicatechin, and pro-cyandins A-1, B-1, and B-2, have been isolated pure from the seed of Areca catechu L., and their 1H and 13C n.m.r spectral data, combined with degradative studies on their reaction with toluene-α-thiol, have established that they all, except for procyanidin B-2, have the C(4)-to-C(8)[or C(6)]-linked (–)-epicatechin stereochemistry [C(2), C(3):cis] in the upper units, and the (+)-catechin stereochemistry [C(2), C(3): trans] in the terminal (lower) units.
The polyphenolics in aqueous extracts of Marion (Rubus sp. hyb) and Evergreen (Rubus laciniatus) blackberries and blackberry seeds were isolated by solid-phase extraction using C18 cartridges and polyamide mini-column chromatography, and characterized using reversed-phase high-performance liquid chromatogra-phy/diode array spectral techniques. Flavonols (primarily quercetin glycosides) were the major phenolics in berries, whereas procyanidins (catechin and epicatechin) and ellagic acid derivatives predominated in seeds. No flavonols were found in seeds. Evergreen berries contained higher level of epicatechin, ellagic acid derivatives, and flavonols than Marion berries, whereas Marion berries and seeds were higher in anthocyanins, total phenolics, and antioxidant properties as measured by oxygen radical absorbance capacity and ferric reducing antioxidant power.
The phenolic compounds (phenolic monomers, polyphenols, tannins) are considered to interfere with iron absorption by complex formation with iron in the gastro-intestinal lumen, making the iron less available for absorption. Very little is known about the extent to which different types of phenolic compounds of different size and chemical structure inhibit iron absorption. The relationship between iron absorption and the amount and type of phenolic compounds was studied by the extrinsic tag method. The aims of the studies were as follows: (i) To study the effect of small phenolic compounds with different hydroxylation patterns (gallic acid, catechin, chlorogenic acid) on iron absorption, (ii) To study the effect of different amounts of a hydrolysable tannin containing ten gallic acid residues (tannic acid) on iron absorption. (iii) To study the degree of inhibition of iron absorption by some foods and beverages (oregano, spinach, coffee and tea) in relation to their respective content of iron-binding phenolic groups, measured by a newly developed method. The inhibition of iron absorption by tannic acid was strongly dose-related. The smallest amount (5 mg) inhibited absorption by 20 per cent, 25 mg by 67 per cent and 100 mg by 88 per cent. Gallic acid inhibited iron absorption to the same extent as tannic acid, per mol galloyl groups, whereas no inhibition was observed when catechin was added to the test meal. Chlorogenic acid inhibited iron absorption to a lesser extent. Oregano and tea inhibited iron absorption in proportion to their respective content of galloyl groups, whereas the inhibitory effect of spinach was less marked. The inhibiting effect of coffee was explained mainly by its content of galloyl groups, but also by some other factor, probably chlorogenic acid. It is concluded that the content of iron-binding galloyl groups might be a major determinant of the inhibitory effect of phenolic compounds on iron absorption from the diet, whereas the phenolic catechol groups seem to be of minor importance. The results further suggest that the group of condensed tannins do not interfere with iron absorption.
The antileishmanial and immunomodulatory potencies of a total of 67 tannins and structurally related compounds were evaluated in terms of extra- and intra-cellular leishmanicidal effects and macrophage activation for release of nitric oxide (NO), tumour necrosis factor (TNF) and interferon (IFN)-like activities. Their effects on macrophage functions were further assessed by expression analysis (iNOS, IFN-alpha, IFN-gamma, TNF-alpha, IL-1, IL-10, IL-12, IL-18). With few exceptions, e.g., caffeic acid derivatives, these polyphenols revealed little direct toxicity for extracellular promastigote Leishmania donovani or L. major strains. In contrast, many polyphenols appreciably reduced the survival of the intracellular, amastigote parasite form in vitro. Upon activation, e.g., by immune response mediators such as IFN-gamma, macrophages may transform from permissive host to leishmanicidal effector cells. Our data from functional bioassays suggested that the effects of polyphenols on intracellular Leishmania parasites were due to macrophage activation rather than direct antiparasitic activity. Gene expression analyses not only confirmed functional data, they also clearly showed differences in the response of infected macrophages when compared to that of noninfected cells. Conspicuously, infected macrophages showed augmented and prolonged activation of host defense mechanisms, indicating that parasitised macrophages were exquisitely predisposed or "primed" to react to activating molecules such as polyphenols. This promotive effect may be of special benefit, e.g., stimulation of the non-specific immune system selectively at the site of infection and when needed. Although these data provide the basis for an immunological concept of plant polyphenols for their beneficial effects in various infectious conditions, in vivo experiments are essential to prove the therapeutic benefits of polyphenolic immunomodulators.
Dietary tannins: consequences and remedies
- S S Kadam
- D K Salunkhe
- J K Chavan
Kadam, S. S.; Salunkhe, D. K.; Chavan, J. K. (1990).
Dietary tannins: consequences and remedies. Boca
Raton: CRC Press. p. 177.
The Natural Organic Tannins
- M Nierensten
- D Sc
M. NIERENSTEN, D.Sc, "The Natural Organic
Tannins"., JCS Churchill Ltd., Portman Square, 108 -150 (1934).