Anthocyanin monoglucosides

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). 

Monomeric anthocyanins represent the sum of the Eve anthocyanin-3-monoglucosides. Wine samples were analyzed by direct injection in the HPLC system (Waters 2690, USA, equipped with a DAD detector). The identification and quantification procedures have been previously described (13). 

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... 

Fig. 6.10. Structure of (a) anthocyanin 3-monogluco-sides, (b) anthocyanins 3-monoglucosides acylated by p-coumaric acid on position 5 of the glucose (Rj and Rj see Figure 6.9)...

Experimentally, Sondheimer (14) for pelargonidin-3-monoglucoside and Berg (15) for malvidin-3-monoglucoside found the values of pK to be close to 3 which is close to the pH of wine. At this pH about 50% of the anthocyanin molecules are in the red form and 50% are in the colorless form. 

The purified anthocyanin chloride, believed to be pelargonidin 3-monoglucoside, obtained by this procedure, had external characteristics which were identical with the product prepared by Sondheimer and Kertesz. 

Analysis by the uv absorption of citrate buffered solutions enables the I anthocyanin to be determined from the maximum at 520nm. The distribution of component anthocyanins can be found by TLC on cellulose with various strongly acidic solvents (eg. cone HCl, formic acid, water, 19 19.5 61.5) of extracts of plant material obtained with 1% hydrochloric acid in methanol. The Rf values found for 3-monoglucosides of the anthocyaninidins of Vitis vinifera were, for the petunidin compound (0.13), for that of malvidin (0.22) and of peonidin (0.25) (ref. 11). ... 

These molecules are much more stable in glycoside (anthocyanin) than in aglycone (antho-cyanidin) form. Only monoglucoside anthocyanins (Figure 6.10) and acylated monoglucoside anthocyanins have been identified in Vitis vinifera grapes and wines acylation is made with p-coumaric (Figure 6.10), caffeic and acetic acids. 

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