Tannin, addition determination

The presence of sulphite cellulosic liquors may be recognised, according to Procter and Hirst, by treating 5 c.c. of the dilute solution (which is used for analysis) with 0-5 gram of aniline and then, after shaking, with 2 c.c. of concentrated hydrochloric acid in presence of such liquors a precipitate is immediately formed and gradually rises to the surface. A more certain indication of the addition of sulphite cellulose liquors may, however, be obtained from a comparison of the results of the determination of the tannin by two methods—indirect and direct (see later). 

With a logwood and chromium ink, without tannin or iron, the addity may be determined directly (after convenient dilution) without addition of indicator, by adding standard potash solution until the violet colour... 

Scalbert et al. (1989) described several methods to determine the concentration of hydrolysable and condensed tannins (proanthocyanidins see Chapter 1, section 3.13.1) in wood extracts. Tannins are complex and heterogeneous In addition to the distinction between the flavonoid-based condensed tannins and the gallic acid-based hydrolysable tannins, each group can display a large degree of chemical variability that can affect the efficacy of the different assays. Interference of chemically related nontannin compounds, such as flavonoids, can in certain cases bias the results. 

The results showed that while none of the books stored in the clean Welsh environment had deteriorated to any significant extent, nearly all the volumes subjected to London s acidic pollution exhibited evidence of decay, some within less than 10 years. In addition, the superior ageing properties of leathers prepared with hydrolysable tannins were confirmed. Of the various chemical analytical determinations undertaken, the only results to show any correlation with the degree of deterioration observed were those for the number of -terminal amino acid groups on the protein. This figure reflects the amount by which the collagen polypeptide chain had been broken and was considered to be evidence for hydrolytic deterioration. 

Ferric-to-Ferrous Reduction— Polyphenols are able to reduce Fe to Fe " " with varying efficiencies. The production of Fe " ions can be monitored by the formation of Prussian blue, Fe4[Fe(CN)6]j. In one assay format (19), 0.2 mL of 8 mM K3Fe(CN)g was added to 3 mL of a 50-pM tannin solution, followed by the addition of 0.2 mL of 0.1 M FeCl3 in 0.1 Af HCl. The optical density was read after 5 min at 700 nm. In a cruder format, the presence of tannins can be determined by the addition of 5% FeCl3/methanol (w/v) solution to an equal volume of sample a brown coloration indicates the presence of polyphenolics. 

Protein Binding—Tannins, as the name implies, characteristically form complexes with proteins based on multipoint hydrogen bonding, and this feature can be used to detect and remove tannins from crude extracts. A visible protein-tannin precipitate should be formed on addition of the tannin-containing extract to a relatively concentrated (approx 5%) solution of bovine serum albumin (BSA). The amount of BSA either remaining in solution or in the precipitate can be analyzed by various protein determination assays. 

Alcoholic beverages contain many substances in small quantities which affect markedly their quality and value. There are present in wines, for example, in addition to alcohol, acids which are volatile with steam, acids which are not volatile, glycerin, tannin, sugars, esters, solids which are converted into an ash when ignited, etc. The quantitative determination of such substances is often valuable in helping to decide upon the genuineness and value of a wine. The details of these processes and the interpretation of the results are considered in books on the analysis of foods. 

The procedure consists of adding 5 ml of cold-soluble gelatin solntion (70 g/1) to 50 ml of red wine. After three days, the wine is centrifuged and the tannins (LA) in the supernatant diluted to 1/50 are assayed to determine the tannin concentration Cl (g/1). Co is the tannin concentration of the control, prior to the addition of gelatin. The gelatin index is given by the equation ... 

Titanium salts can also be determined using cupferron (the ammonium salt of nitrosophenylhydroxylamine) [20] or tannin [21]. In addition, 2 -hydroxy-4 -methylpropiophenone oxime has been shown to form an insoluble 1 1 complex with Ti salts [22]. 

The adhesives developed for the manufacture of damp-ply-resistant corrugated cardboard are based on the addition of spray-dried wattle extract, urea-formaldehyde resin, and formaldehyde to a typical Stein-Hall starch formula with 18-22 per cent starch content [75, 76]. The wattle tannin-urea-formaldehyde copolymer formed in situ and any free formaldehyde left in the glue line are absorbed by the wattle tannin extract. The wattle extract powder should be added at level of 4—5 per cent of the total starch content of the mix (i.e. carrier plus slurry). Successful results can be achieved in the range of 2-12 per cent of the total starch content, but 4 per cent is the recommended starting level. The final level is determined by the degree of water hardness and desired bond quality. This wattle extract UF-fortifier system is highly flexible and can be adapted to damp-proof a multitude of basic starch formulations. 

Rather than distilling 100 ml. from 10 ml. of wine several short cuts have been proposed. Foucy (1932) used the 100-ml. distillate from 50 ml. of wine for determining the volatile acidity. Although he found a fairly constant fraction of the acids to distill from synthetic solutions, this is by no means true of wines of very variable composition. Direct distillation of 72% of the wine and doubling the titration value has been tested by Violante and Imbrici (1949). On 34 of 35 samples their results were within 0.007% of those by steam distillation and the usual difference was 0.003. Procopio (1948c) also distilled a fixed amount of the wine and applied an appropriate correction factor. Rentschler and Simmler (1949) proposed distilling 5 ml. of wine after addition of tartaric acid and tannin. The apparatus is simple, and the determination requires only 7 to 10 minutes. 

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