Phenolic pigments anthocyanins

Hundreds of applications have been mentioned in the Zweig (1968) review acids, alkaloids, amino acids, antibiotics, antioxidants, food and feed additives, bases and amines, bile acids, carbonyls, dyes, enzymes, lipids, hydrocarbons, hormones, indoles, natural products, peptides, proteins, pesticides, plant growth regulators, pharmaceutical products, phenols, pigments (chlorophylls, xanthophylls, porphyrins, melanin, pterins, pteridines, anthocyanins, ilavonoids, etc.), polymers, purine and pyrimidine derivatives, quinones, RNA, DNA, organic sulfur compounds, steroids, sugars, toxins, vitamins, inorganic ions, and others. 

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. 

As extensive research into anthocyanin has been conducted over the years, a large amount of information is available on which pigments are found in a particular fruit. This allows an analyst to assess whether a sample contains the expected pigments and to determine whether there are any added from another source or fruit. A very good reference book which details the anthocyanins found in various plants and also gives details of other phenolic materials found in fruits is Macheix s book on plant phenolics (Macheix el al., 1990). 

Betacyanins are red pigments and account for the red color of beets (Beta vulgaris). They are unique compounds to the Centrospermae. They have absorption spectra that resemble anthocyanins, but they contain nitrogen. An example is betanidin (1.66). Betacyanins are normally found as glycosides. Betaxanthins are chemically related to betacyanins, but they are not phenols. An example is indicaxanthin (1.67). These compounds are yellow pigments, and are also unique to the Centrospermae. 

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