Anthocyanins structures

Timberlake, C.F. and Bridle, P., Flavylium salts anthocyanidins and anthocyanins. Structural transformations in acid solutions, J. Sci. Food Agric., 18, 473, 1967. 

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. 

This chapter follows on from those of the four previous editions of The Flavonoids,and the three review articles of Harborne and Williams. It will confine its attention largely to a detailed account on anthocyanin structures reported after 1992 (Section 10.2 and Table 10.2). Special effort has been made to present a comprehensive overview of all the various anthocyanins with complete structures in the literature (Section 10.2 and Appendix A). Many anthocyanins reported in checklists of previous reviews have been excluded from Appendix A mainly because of the lack of experimental proofs for proper determination of the linkage point(s) between one or more of the glycosidic units involved. For instance, after careful considerations of the data used as evidence for determination of the linkage position of the monosaccharides in the different anthocyanidin 5-monoglycosides presented in the various reports in the literature, we have excluded these anthocyanins apart from the deox-yanthocyanidin 5-glycosides from Appendix A. 

Prior RL, Wu X. 2006. Anthocyanins Structural characteristics that result in unique metabolic patterns and biological activities. Free Rad Res 40 1014-1028. 

Figure 5.2 Selected sugars and aromatic or aliphatic acids that commonly occur in anthocyanin structures. Sophorose = 2-O-b-D-glucopyranosyl-D-glucose rutinose = 6-O-L-rhamnosyl-D-glucose sambubiose = P-D-xylosyl-(l 2)-P-D-glucose.

Figure 5.3 Simplified diagram of anthocyanin structural transformation in solution. A flavylium cation, B the quinoidal base, C the hemiacetal base, D chalcone. (Gly glycoside) (Modified from Mazza and Miniati, 1993).

Figure 1.1 Common anthocyanin structures. Sugar moieties are generally on position 3 of the C-ring.

Flavonoids, physicochemical and analytical characteristics of 88MI47. Highly acylated anthocyanins, structure, stability and intramolecular stacking of 88YGK426. 

Surprisingly, the absorption varied widely from 19 to 37%, depending on the individual anthocyanin structure in the bilberry extract. Delphinidin 3-0-arabinoside (91) showed the highest absorption rate (37%). 

In aqueous media, most of the natural anthocyanins behave like pH indicators, being red at low pH, bluish at intermediate pH, and colorless at high pH. According to Brouillard (1982), in acidic and neutral media four anthocyanin structures exist in equilibrium the red flavylium cation (AH+), blue or red quinonoidal base (A), colorless carbinol pseudobase (B), and colorless chalcone (C) (Reaction 9.3). 

The stable tannin-ethyl-anthocyanin structures are apparently transformed at varying rates into orange compounds, via the fixation of the polarized double bond of the vinyl-procyanidins on the anthocyanins, to form procyanidin-pyranoantho-cyanin complexes (Francia-Aricha et al., 1997). The rate of conversion depends on the wine s phenol content, the origin of the tannins (skins or seeds), and the phenolic structures (tannin-anthocyanin combinations) present at the end of the aging period. 

Further substitution reactions carried out by acyltransferases (acylation of sugars) and/or methyltransferases (methoxylation of hydroxyl groups) yield different anthocyanin structures as presented on Figure 5. 

Figure 10 presents some selected cyanidin derived anthocyanin structures observed in various berries. 

The natural occurrence of individual anthocyanin structures in different berry sources according to the literature sources referenced throughout this document is shown on Table 4 [68-81]. 

Only for dietary supplements or processed food samples, extraction of anthoeyanins followed by solid phase purification with subsequent analysis by HPLC with UVA/ IS detection is performed as first level analysis. The matrix in those samples is complex and may include synthetic colorants in accordance with applicable food legislation, hence simple UVA IS analysis would yield most certainly erroneousness results. At this stage of analysis a decision is necessary on whether or not HPLC/MS analysis has to be performed. HPLC/ MS is powerful for the confirmation of anthocyanin structures but seldom useful for quantification as the calibration is complicated and robustness is low. 

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