Color, pigments tannins

The anthocyanins (colored pigments) and tannins (astringent substances) in wines have greater antiviral effects than unfermented grape juice. However, these experiments were conducted in laboratory vessels, rather than in animal or human subjects. 

The first method uses the fact that in acid media anthocyanins exist in a colored and a colorless form (9 and 10) in equilibrium, with the position of the equilibrium depending on pH. Consequently, the difference in color intensity between the two pH values (0.6 and 3.5 for example) is proportional to the pigment concentration. Since the phenol function is not affected by this variation, other phenolic compounds, especially tannins, do not interfere since their absorption at 550 nm is the same at both pH values. 

The anthocyanin is malvidin-3,5-diglucoside (Fluka), and the tannins are a sample of leucoanthocyanins extracted from the bark of the maritime pine (Pinus pinaster). The products are not identical to the natural grape pigments nevertheless, it may be assumed that the observed facts correlate, as a first approximation, with red wine color and its changes. 

This reaction was confirmed in another experiment (17) using standard tests which followed the evolution of pigments in identical mixtures in tubes 1, 2, and 3 for two months. After allowing the tannins to react it appears that the anthocyanins contribute to the color of the solution to a limited extent. 

Red wine color does not depend exclusively on the anthocyanin and tannin levels the physicochemical state of these pigments also exerts an influence. Related wine types, especially those of the same age, can have colors which may not be interpreted solely on the basis of anthocyanin and tannin levels. 

Dry white table wines differ from red table wines in characteristics other than color. They contain lower concentrations of the puckery and astringent tannins. They usually have a higher acid content which makes them somewhat lighter in body and fresher on the palate. Dry white wines also are usually simpler in their aroma in contrast to the complicated aroma and bouquet that can develop in a red table wine. While it is possible to make white table wines from red-skinned varieties, for the home winemaker this task is very difficult because it is almost impossible to remove all traces of the pigment-containing skins from the juice quickly enough to prevent some reddish or amber color from developing. 

Colors of finished sorghum starch are related to the intensity of pericarp colors.128 Steepwater color, and probably its tannin content, varies with the intensity of the pericarp pigments. Some varieties contain pigments that are colorless at acid pH, but are bright yellow at pH 9-10. These pigments cause starch to have a gray cast which can be improved by bleaching.129... 

Note "Tanning Chemicals, Dye, Paint, Putty Inks" refers to "tanning or dyeing extracts tannins and their derivatives dyes, pigments and other coloring matter paints and varnishes putty and other mastics inks," HS (Harmonized Commodity Description and Coding System) Code 32. 

Condensed tannins, on the other hand, occur in the bark of all conifers and hardwoods examined to date, and they are frequently present in the wood. They are primarily responsible for the tan to brown color of wood after it is exposed to air. In their purest form, condensed tannins are colorless, but they become colored very readily once isolated because of their propensity to oxidize to quinones. The primary characteristic of the water-soluble condensed tannins (4) is dehydration/oxidation to intensely colored anthocyanidin pigments (5) when refluxed in butanol and hydrochloric acid (Figure 2). For this reason, there has been a tendency to refer to these compounds as proanthocyanidins in the last few years. Prior to that, they were referred to as leucoanthocyanidins (i.e., the colorless chemical form of anthocyanidins). All references earlier than the late 1950 s, when the structure of these substances was just beginning to be understood, used the term condensed tannin. 

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