Anthocyanins aglycones

Macz-Pop, G.A. et al.. Natural occurrence of free anthocyanin aglycones in beans (Phaseolus vulgaris L.), Food Chem., 94, 448, 2006. 

Matsumoto, A., Nakamura, Y., Hirayama, M., Yoshiki, Y, and Okubo, K., Antioxidant activity of black currant anthocyanin aglycons and their glycosides measured by chemiluminescence in a neutral pH region and in human plasma, J. Agric. Food Chem., 50, 5034-5037, 2002. 

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. 

Anthocyanins are poorly absorbed from the gastrointestinal tract and the mechanisms involved remain unclear. These compounds are usually recovered in very small amounts in human serum after oral ingestion (less than 1% of the dose) or in the IN fraction after in vitro digestion (about 5%). ° Unlike other polyphenols, anthocyanins constitute an exception because intact glycosides are recovered in the body (without deglycosylation prior to absorption). - This may be explained by either the instability of the free aglycone form or by a specific mechanism of absorption for anthocyanins. 

Petnnidin was detected in amounts above 10% of the total anthocyanin content in only 4 of the 44 frnits listed in Table 4.3.1, in 1 of 13 vegetables shown in Table 4.3.3, in 2 kinds of beans and in 1 nut (Table 4.3.4). Petunidin was found in different grape species snch as cv. Cabernet Sauvignon, ° variety Isabelle, " cv. Pallagrello, cv. Piedirosso Vesnvio, " cv. Nerello Mascalese, and cv. Clinton." None of the foods listed in the fonr tables presented petnnidin as the sole aglycone. 

Andersen, 0.M. et al., Anthocyanin from strawberry (Fragaria ananassa) with the novel aglycone, 5-carboxypyranopelargonidin, Phytochemistry, 65, 405, 2004. 

Fossen, T. and Andersen, 0.M., Anthocyanins from red onion. Allium cepa, with novel aglycone. Phytochemistry, 62, 1217, 2003. 

Many solvents such as methanol, acetone, ethanol, and water are used for anthocyanin extraction due to their polar character since most anthocyanins occur naturally as glycosides. Anthocyanin glycosides have higher solubility in water than the corresponding aglycons. In addition, in most fruits and vegetables, anthocyanin pigments are located in cells near the surface. " ... 

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. 

Fernando and Senadeera [40] used different natural pigments incorporating anthocyanins that were extracted from various tropical flowers. The extract was acidified to p H < 1, assuming a deeper coloration, and was used for the preparation of the photovoltaic apparatus. The generation at pH <1 of the oxonium ion allows the wide conjugation of the Jt-electron density throughout the aglycone portion of the... 

---