High molecular weight tannins

Tannins are widely distributed in plant flora. They are phenolic compounds of high molecular weight. Tannins are soluble in water and alcohol and are found in root, bark, stem and outer layers of plant tissue. Tannins have a characteristic feature to tan, i.e. to convert the things into leather. The tannins are acidic in reaction and it is attributed to the presence of phenolic or carboxylic group. Tannins form complex with proteins, carbohydrates, gelatin and alkaloids. 

Presence of high-molecular-weight tannins in the extract [28,42,45]. 

The high viscosity of tannin extract solutions has also been correlated with the proportion of very-high-molecular-weight tannins present in the extract. This effect is not well defined. In most adhesive applications such as in plywood adhesives, the viscosity is not critical and can be manipulated by dilution. 

These condensed tannins and their derivatives, all of high molecular weight, function as anionic polyelectrolyte sludge conditioners, tending to sequester hardness salts and hinder their precipitation as crystalline scales. In addition, when precipitation does occur, the condensed tannins coagulate the particles, resulting in a mobile sludge that can be easily blown down. 

HAGERMAN A E, RIEDL K M, JONES G A, SOVIK K N, RITCHARD N T, HARTZFELD P W and RIECHEL T L (1998) High molecular weight plant polyphenohcs (tannins) as biological antioxidants, J Agric Food Chem, 46, 1887-92. 

Tannins are polyphenolic compounds of high molecular weight that occur naturally and react with proteins. They can form insoluble complexes with proteins, which are responsible for the taste known as astringency that is caused by precipitation of mouth proteins. Tannins are typically classified into three groups (1) the condensed tannins, (2) the hydrolyzable tannins, and (3) the phlorotannins (Figure 11.3.10). 

Tannins (Figure 11.3.10) are polyphenolic polymers of high molecular weight that occur naturally and react with proteins. Tannins are... 

Tea leaves consist primarily of cellulose this is the principle structural material of all plant cells. Fortunately, the cellulose is insoluble in water, so that by using a hot water extraction, more soluble caffeine can be separated. Also dissolved in water are complex substances called tannins. These are colored phenolic compounds of high molecular weight (500 to 3000) that have acidic behavior. If a basic salt such as Na2C03 is added to the water solution, the tannins can react to form a salt. These salts are insoluble in organic solvents, such as chloroform or dichloromethane, but are soluble in water. 

Table 10. Contents of low molecular weight (LMP) and high molecular weight (HMP) phenolic derivatives in aerial parts of typical plant species from an exposed grassland slope of the northern Andes to 2100 m asl. LMP amounts are in mg equiv of salycilic acid g w/w and HMP are in mg equiv of quebracho tannin g w/w. Unusually large amounts may be due to differences in oxidation potential relative to the standard. Errors are one SD. Data from Alonso-Amelot et al. 2005.

Despite these advances, it is generally accepted that the vast majority of die observed color in aged red wine remains to be characterized. The obvious factor that separates characterized compounds from uncharacterized compounds appears to be molecular weight, with much of the high molecular weight material being unknown in structure. What is apparent is that as wine ages, the observed red color increases in size, apparently due to interaction between anthocyanins and proanthocyanidins (tannin) (10). 

A study of the freezing points of solutions of the tannins has yielded results that lead to the conclusion that they all possess very high molecular weights,—a fact in accord with their colloidal properties. Since the number of compounds formed as the result of their hydrolysis is relatively small it is probable that they are the result of the condensation, with the loss of the elements of water, of hydroxy benzoic acids, such as gallic acid and protocatechnic acid. Emil Fischer who studied this class of... 

HIGH MOLECULAR WEIGHT PLANT POPLYPHENOLS (TANNINS) PROSPECTIVE EUNCTIONS... 

High Molecular Weight Plant Polyphenols (Tannins) Prospective... 

Electrospray ionization (ESI) recently developed in connection with LC/MS is superior to FAB in the soft ionizations of labile high molecular weight compounds, and has the advantage of producing predominant pseudo-molecular ions such as [M+H]+ or [M+Na]" for the ionic minute compounds. The ionization effect in ESI-MS depends on whether the solvent contains acetic acid, formic acid or trifluoroacetic acid etc. This technique with direct injection has been successfully applied to hydrolyzable tannins up to tetramers when 50% aqueous MeOH or 50% aqueous acetonitrile containing a small amount of ACONH4 was used as a solvent. In this condition, the observed molecular ion species for hydrolyzable tannins are an [M+NH4] with high sensitivity. 

The content of condensed tannins in hazelnut (kernel), expressed as milligrams of CE per gram of extract, varies quite markedly, from a low of 40.5 for 80% ethanolic extract to a high of 320 for 80% acetone extract. Acetone is a more effective solvent for the extraction of condensed tannins as tannins are relatively high-molecular-weight compounds and ethanol is not necessarily suitable for their extraction [30]. The reason for this is that tannins are relatively high-molecular-weight compounds and the polarity of ethanol is too low for total extraction of these polar compounds from plant sources. 

Hagerman, A.E., Riedl, K.M., Alexander Jones, G., Sovik, K.N., Ritchard, N.T., Hartzfeld, P.W., and Riechel, T.L., High molecular weight plant polyphenolics (tannins) as biological antioxidants, J. Agric. Food Chem., 46, 1887-1892, 1998. 

Presence of high-molecular-weight hydrocolloid gums in the tannin extract [42,45]. The viscosity is directly proportional to the amount of gums present in the extract [42,45]. 

Prooxidant activity of phenolic compounds Phenolic antioxidants can initiate an autoxidation process and act like prooxidants under conditions that favor their autoxidation. Instead of terminating a free-radical chain reaction by reacting with a second radical, the phenoxy radical may also interact with oxygen and produce quinones (P = 0) and superoxide anion (02 ). PO -I-O2—>P = 0- -02 . Small phenolic compounds which are easily oxidized, such as quercetin, gallic acid, possess prooxidant activity while high-molecular weight phenolic compounds, such as condensed and hydrolyzable tannins, have little or no prooxidant activity. 

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