Anthocyanidin aglycone

The fundamental nucleus in anthocyanidins (aglycones) is flavylium chloride. Most of the anthocyanidins are derivatives of 3,5,7-trihydroxyflavylium chloride. Thus, the hydroxylation patterns in the natural anthocyanidins fall into the three basic groups of pelargonidin, cyanidin and delphinidin. Anthocyanidins are rarely found in fresh plant material because of their instability [19]. 

The basic chemical structure of anthocyanidins (aglycone) is shown in Figure 5.1. Over 600 naturally occurring anthocyanins have been... 

Anthocyanidins (aglycones), flavyliun salts (chlorides), are shown generally by (1), the anthocyanins (3-monoglucosides) by (2), and 3,5-diglucosides by (3). The major anthocyanidins are cyanidin, delphinidin, malvidin, pelargonidin, peonidin and petunidin and the substituents in their structures are shown below for the formula (1). Table 3... 

Anthocyanins can be quantitated as intact glycosides or as anthocyanidin aglycons by UVA IS-spectroscopy. Anthocyanins can be directly measured after suitable extraction from the source material or can be hydrolyzed to the corresponding anthocyanidin aglycons before measurement. UVA IS-spectroscopy provides an absorption value which is indicative for the sum of anthocyanins present in a sample. The test results are not indicative for the presence or amount of individual anthocyanins. A special problem is the adulteration of anthocyanins with synthetic red food colorants which absorb at the same wave lengths as anthocyanins. 

Anthocyanins are water-soluble glycosides of anthocyanidins and are part of the phenolic group known collectively as flavonoids (see Section III). The anthocyanidins (aglycones) are polyhydroxy... 

As we have seen above, anthocyanins comprise an aglycone fraction commonly known as anthocyanidin and a frequently acylated osidic substituent. This characteristic leads to two different approaches for the analysis of these pigments (1) a direct anthocyanin analysis without a hydrolysis stage requiring identification of a number of molecules (several hundreds in the plant kingdom) or (2) an analysis of the anthocyanidin fraction only after hydrolysis of the anthocyanins present in the medium. 

Malvidin was detected in amounts greater than 10% of the total anthocyanin content only in 4 of 44 fruits listed in Table 4.3.1, in none of the 13 vegetables shown in Table 4.3.3, and in 2 grains and nuts presented in Table 4.3.4. Malvidin is widespread in all types of grapes being one of the major anthocyanidins found in grapes shown in Table 4.3.2. None of the foods listed in the tables presented malvidin as the sole aglycone. 

The numbers and types of fragments depend on the anthocyanin structure pattern. The aglycone (anthocyanidin) ordinarily is very stable and cannot be broken easily. In most cases, cleavage of the glycosidic groups will occur to generate small amounts of anthocyanidins in addition to the intact anthocyanin molecular ions. 

Anthocyanins are the deeply colored glycosides of the aglycone anthocyanidins. Only the six aglycones shown in Figure 13.6 are common, although others occur sporadically [11,12]. 

Anthocyanins and anthocyanidins are readily separated on cellulose layers using developing solvents consisting hydrochloric acid-formic acid-water in differing proportions [24]. Glycosides and aglycones are readily separated on the same plate, provided that a sufficiently polar solvent is employed. 

Fig. 2.112. The structures of the flavan-3-ol(4a — 8)pelargonidin 3-0-/f-glucopyranosides (1-4) isolated from strawberry extract. The letter A denotes the aglycone ring systems belonging to the anthocyanidin substructure, whereas the letter F denotes the aglycone ring system belonging to the flavanol substructure. Reprinted with permission from T. Fossen et al. [252].

There are five anthocyanidins in the grape delphinidin 1, petunidin 2, malvidin 3, cyanidin 4, and peonidin 5. These aglycones exist in different heterosidic forms or as anthocyanins 3-monoglucosides, 3,5-diglucosides, and acylated heterosides, whose structures, in the case of malvidin, are represented by formulas 6, 7, and 8. In the acylated anthocyanins, one molecule of cinnamic acid, more generally p-coumaric acid, is esterified with the —OH group in the sixth position of a glucose molecule (12). 

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