Anthocyanidins definition

By definition procyanidins and anthocyanogens, on treatment with acid, give anthocyanidins which show maximum light absorption at about 545 nm. By measurement at 455 nm estimates of the amount of catechin present can also be obtained [51]. The yield of anthocyanidin from different procyanidin fractions varies and anthocyanogen values do not correlate with the shelf life of beers. In many cases the yield of anthocyanidin released by add decreases as the procyanidins polymerize while the level of total polyphenols (EBQ remains roughly constant. Accordingly the... 

In many types of plant tissue, colorless materials are present which, upon treatment with mineral acids, are converted to red substances exhibiting many of the properties of anthocyanidins. The colorless compounds were given the names of leucoanthocyanins and leucoanthocyanidins by Rosenheim (6), These compounds probably represent a heterogeneous class. They may have an important part in bleaching and color-stabilization problems, particularly in the western areas of the United States, where many woods have a reddish rather than the more usual yellowish cast. Although work has been done, particularly by the Robinsons, the structures of the leucoanthocyanins have not been established definitely. 

Although earlier reviews by Haslam (134-136) discuss the many problems that have arisen about the systematic classification and nomenclature of proanthocyanidins, it seems useful to repeat the definition of the term proanthocyanidin as initially established by Freudenberg and Weinges (116) - the proanthocyanidins are all the colorless substances isolated from plants which, when treated with acid, form anthocyanidins. Thus the leucoanthocyanidins (now restricted to the flavan-3,4-diols), the condensed tannins (Sect. 7.7), and any other colorless flavonoid derivatives that produce anthocyanidins on heating with acid should be grouped under this class of compounds. 

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