Tannin research

The leather-tanning industry of India used about 120000 tons of assorted vegetable tannins in 1970 (203). India imported about 25000 tons of wattle extracts to supplement domestically available tannins such as myrobalan nut tannins (3500 tons/year) and wattle tannins (2000 tons per year). Vegetable tannins (primarily mixtures of chestnut, wattle, and quebracho tannins) are also used widely in Italy (173). In the Peoples Republic of China, much of the leather manufactured is made using vegetable tannins. Research efforts are being accelerated on the use of tannins from indigenous plants such as Larix and Firms spp. (Sun and Foo, personal communication 1986). 

Because of the time and expense involved, biological assays are used primarily for research purposes. The first chemical method for assaying L-ascorbic acid was the titration with 2,6-dichlorophenolindophenol solution (76). This method is not appHcable in the presence of a variety of interfering substances, eg, reduced metal ions, sulfites, tannins, or colored dyes. This 2,6-dichlorophenolindophenol method and other chemical and physiochemical methods are based on the reducing character of L-ascorbic acid (77). Colorimetric reactions with metal ions as weU as other redox systems, eg, potassium hexacyanoferrate(III), methylene blue, chloramine, etc, have been used for the assay, but they are unspecific because of interferences from a large number of reducing substances contained in foods and natural products (78). These methods have been used extensively in fish research (79). A specific photometric method for the assay of vitamin C in biological samples is based on the oxidation of ascorbic acid to dehydroascorbic acid with 2,4-dinitrophenylhydrazine (80). In the microfluorometric method, ascorbic acid is oxidized to dehydroascorbic acid in the presence of charcoal. The oxidized form is reacted with o-phenylenediamine to produce a fluorescent compound that is detected with an excitation maximum of ca 350 nm and an emission maximum of ca 430 nm (81). 

Min, B. R., Pomroy, W. E., Hart, S. P. and Sahlu, T. (2004). The effect of short-term consumption of a forage containing condensed tannins on gastro-intestinal nematode parasite infections in grazing wether goats . Small Ruminant Research, 44, 81-87. 

Much work has been done on the removal of Pb and Zn from aqueous solution. Removal of these ions has been attempted by several researches employing a wide variety of techniques. Adsorption of removal of Pb and Zn from solution agricultural waste [5], three fern [6], tannin gel [7], removal of Pb sea module [8], tannin gel adsorbent synthesized from condensed tatmin [8] and removal of Zn green macro alga [9], soil [3] have been extensively studied for this purpose. 

Microbial Degradation of Catechin. Since (+) catechin is a possible biodegradation product from condensed tannins, its utilization and bioconversion have been extensively examined by several research groups using fungi, bacteria and yeasts. 

Subsequently, a series of Investigations by a group at the Western Regional Research Center In California and associates have shown condensed cotton tannin to be an antibiotic chemical for the bollworm, tobacco budworm, and pink bollworm (13, 14,... 

Phenolic compounds and flavonoids are a unique category of plant phytochemicals especially in terms of their vast po ential health-benefiting properties. They represent the most abundant and the most widely represented class of plant natural products. A substantial amount of research has been carried out over the past two decades yet large information gaps still exist. For example, the inventory of these compounds is still incomplete, although there is continuous effort to provide new structures. In addition the dissection of the metabolic pathways for certain phenolic compounds remains to be resolved. Recent reports underline that important questions that still need to be answered in the field of proanthocyanidin and tannin biosynthesis [Xie and Dixon, 2005], and even the exact nature of the biosynthetic pathway(s) leading to lignin monomers is not fully elucidated. 

The objective of this symposium was to include research on a broad range of natural products directed to a wide variety of bonding applications. The speakers described research on adhesive polymers derived from lignins, tannins, carbohydrates, terpenes, and proteins for applications as diverse as tire-cord bonding and eye surgery. 

In this chapter, the development of a thermosetting adhesive from soda bagasse lignin is described. The research has concentrated on the development of interior-grade adhesives for particleboard. The local market for exterior boards is smaller than that for the interior panels, and adhesives for exterior boards are already covered by an excellent range of tannin-based adhesives. 

Interest in use of condensed tannins as components of adhesive formulations began about three decades ago. While research studies have been carried out in widely scattered laboratories around the world, three major areas of activity can be distinguished. These are 1) development of bark extracts and commercial production facilities on the west coast of North America, 1953 to 1975 2) application of tannins in adhesive formulations in South Africa based on indigenously produced mimosa (wattle) tannin, early 1970 s to the present and 3) a resurgence of interest in pine bark as raw material for tannin-based adhesives, beginning in the middle 1970 s. Each of these activities has been characterized by parallel efforts on structural identification of the tannins and development of unique methods for incorporating the isolated tannins into adhesives. 

Although preliminary studies suggest that face-laminations can be obtained using adhesives made from condensed tannins that pass the standards of the American Institute of Timber Construction (< ), less is known about how to formulate adhesives using these materials for end-jointing of wood. This study, funded by the USDA Small Business Innovation Research Program, was undertaken to develop adhesive formulations containing 50% of sulfite extracts obtained from the bark of southern pine trees and demonstrate their use in... 

Kreibich, R. E., Use of Bark Tannins in End-Joint Adhesives for Wood. Final Report-Phase I to the USDA Small Business Innovation Research Program on grant 86-SBIR-8-0126, R. E. Kreibich, Auburn WA., 1987. 

---