Total tannins, analysis

Singleton and Esau (I) reviewed the methods for phenol analysis of wine. They pointed out that study would be greatly advanced if one could determine the total content of phenolic substances and express it in such a way that analysis of subclasses of phenols could be related to the original total and a balance sheet could be obtained. One could then say, for example, this wine has a total phenolic content of 1200 mg/liter calculated as gallic acid, and of that total, cinnamic acid derivatives account for 200 mg/liter, anthocyanins for 300 mg/liter, other small flavonoids for 200 mg/liter, and condensed tannins complete the total with 500 mg/liter of gallic acid equivalent. To accomplish this, the total phenol analysis not only must meet ordinary criteria of reproducibility and precision, but it also must be based on chemical relationships such that fractions determined separately can be converted to units of the total. Of course when clearcut fractionation can be accomplished by... 

Swain T, Hillis WE (1959) The phenolic constituents of Prunus domestica. I. The quantitative analysis of phenolic constituents. J Sci Food Agric 10 63-68 Taira S, Shimomura M, Oba S, Watanabe S (1990) Changes in soluble and total tannin content during fruit development and their relation to removal of astringency in Japanese persimmon Diospyros kaki Thunb.). Abstr XXIII Int Horticultural Congr, 27 Aug-1 Sept 1990, Firenze, vol 2, no 3279... 

Ruffed grouse, B. umhellus, feed on staminate flower buds and extended catkins of trembling aspen, P. tremuloides. In winter these birds select specific trees or clones. Analysis for alkaloids, tannins, and other phenolics showed that feeding preferences were not related to the levels of tannin or total phenolics in... 

Quantitative Analysis of Tannins. Beginning with determinations for total phenolic compounds, all attempts to isolate compounds related to tannins—i.e., those forming stable compounds with proteins—have been unsatisfactory. Hence, one cannot use this as the basis for an analytical method. 

Quantitative analysis of tanning products (raw materials and extracts) requires firstly rational sampling and then suitable preparation of the sample and solution, and includes mainly determinations of the total soluble matters, the tannins and non-tannins, water and insoluble substances.1 Other determinations sometimes made are those of the ash, sugar and sulphurous anhydride, and in industrial practice the specific gravity and colour of the solutions are often measured. 

In any event, even if aging in oak barrels increases the phenol content of wine, it is by no means snre that it increases the overall tannin content, at least in red wines. Analysis has shown that the total phenol index (OD 280) only increases by a few nnits dne to wood tannins, compared to an initial valne between 50 and 60. Of course, the increase is proportionally more significant in white wines, with their much lower initial tannin content. 

---