Color, pigments flavonoids

Flavonoids are more or less intensely yellow colored pigments belonging either to the group of 2-phenyl-chromones 39 (flavones, flavonols) or 2-phenyl-chromanones 391 (flavanones, flavanonols) both groups have a backbone of 2-phenyl-l,4-benzopyrones ... 

The flavonoids (Figure 2B) are yellow-colored pigments that give the pale yellow color to white wines. They are also present in red wines but their color is masked by the anthocyanins (Figure 2C), the coloring substances of red wines. Like the anthocyanins, the flavonoids exist primarily as heterosides where the 3-position on the heterocycle contains a sugar moiety. The latter may in turn be acylated with cinnamic acid, which confers greater stability on the molecule. 

Three of these common flavonoid compounds, pelargoni-din (4), cyanidin (3), and delphinidin (2), are anthocyanidins. These colored pigments are found widely in flowers and fruits and frequently are involved in the attraction of pollinators and in fruit and seed dispersal, but they also occur in vegetative portions of plants. 

Anthocyanins from various berry sources are a very interesting group of colored pigments of the flavonoid family as they serve as natural colorants and as functional food ingredients. 

The majority of the plant pigments hitherto isolated from woods in pure form are the flavonoids, such as flavone, flavanone, isoflavone, isoflavanone, pterocar-pane, and chalcone derivatives, along with the phenols stilbene and xanthone, which are almost white or yellow in color. Other flavonoids such as aurone and neoflavone derivatives (orange pigments) have a limited distribution and sometimes occur as wood extractives in species of the Anacardiaceae and Leguminosae (4, 7). The presence of the typical anthocyanin derivatives of flowers and fruits is extremely rare in wood, but their leuco-compounds such as flavan-3-ol and flavan-3,4-diol have been found to occur in the wood of a considerable number of tree species (14). Besides anthocyanidin, the few other deep-colored (red, purple, or blue) pigments from woods usually possess a quinone structure. 

Yellow Lake Pigments, Identification and Study of Deterioration of Flavonoid Colorants. Arie Wallert and N. Wyplosz, Molecular Aspects of Ageing in Painted Works of Art, Progress Report 1995-1997, FOM Institute for Atomic and Molecular Physics, Amsterdam, NL, http //www.amolf.nl/research/biomacromolecular mass spectrometry/ molart/progress report98.pdf... 

Anthocyanins are colored flavonoids that attract animals when a flower is ready for pollination or a fruit is ready to eat. They are glycosides (i.e., the molecule contains a sugar) that range in color from red, pink, and purple to blue depending on the number and placement of substitutes on the B ring (see Fig. 3.7), the presence of acid residues, and the pH of the cell vacuole where they are stored. Without the sugar these molecules are called anthocyanidins. The color of some pigments results from a complex of different anthocyanin and flavone molecules with metal ions. 

Some structural changes of the native flavonoids occur during wine conservation, and one of the most studied of those changes concerns red wine color evolution, called wine aging. It has been demonstrated that as a wine ages, the initially present grape pigments slowly turn into new, more stable red pig-... 

The W1 locus encodes flavonoid 3 5 -hydroxylase F3 5 H) [21]. F3 5 H diverts metabolic flux into the blue delphinidin branch of anthocyanin biosynthesis (Fig. 4.1). In the absence of F3 H activity (f), Wi and recessive wl give imperfect black and buff seed colors, respectively [10]. However, in black seeds, F3 H (T) phenotypically masks Wl. In contrast to its role in seeds, Wl has a prominent role in flower colors, as delphinidin-based anthocyanins are the major pigments in purple soybean flowers [22, 23]. Interestingly, F3 5 H is expressed at very low levels in flowers and seeds [21]. This suggests that, out of the two branch-point genes (i.e., F3 H and F3 5 H), it is the strong expression of F3 H in seed coats and weak expression in the flowers that determines preferential accumulation of cyanidin-based and delphinidin-based anthocyanins in these respective tissues [21]. 

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