Aglycones absorption

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. 

The application of standardized UV (or UV-Vis) spectroscopy has for years been used in analyses of flavonoids. These polyphenolic compounds reveal two characteristic UV absorption bands with maxima in the 240 to 285 and 300 to 550 nm range. The various flavonoid classes can be recognized by their UV spectra, and UV-spectral characteristics of individual flavonoids including the effects of the number of aglycone hydroxyl groups, glycosidic substitution pattern, and nature of aromatic acyl groups have been reviewed in several excellent books. ... 

Commelinaceae) shows an extra absorption band at 583 nm at pH values above 4.0, which makes this pigment highly colored at these pH values.The high stability of this type of pigments with as much as four acyl units was assumed to be due to the difficulty of water molecule diffusion to the hydrophobic center formed by the acyl groups and the aglycone. 

The absorption of intact quercetin glycosides has been demonstrated by some authors [64,65,76]. Hollmann demonstrated in ileostomy subjects (who lack colon with the bacterial flora, thus circumventing the problem of microbial degradation), that the quercetin glycosides from regular foods (onions, tea) were far better absorbed than pure aglycone (52% vs 24%). 

The aglycone of betaniu, the red-violet pigment of the beet (Beta vulgaris var. rubra), known as betanidin, has recently been shown to have the structure depicted in structural formula 113.170,282 Betanidin had previously been reported by Piattelli and Minale to contain a dopachrome unit in its structure and consequently would have been formulated as 114.109 The Italian workers obtained pyrrole-2,3,5-tricarboxylic acid and pyridine-2,4,6-tricarboxylic acid on permanganate oxidation of betanidin and they also prepared a semi-carbazone of the pigment, the absorption spectrum of which showed the pH dependency expected for an aminochrome semicarbazone.169... 

Most phenolic glycosides are water soluble, but the corresponding aglycones are usually less so. Phenolic substances are aromatic and therefore show intense absorption in the UV region of the spectrum (2). Most of the benzoic acid derivatives displayed their maxima at 246-262 nm, with a shoulder at 290 - 315 nm, except gallic and syringic acid, which have absorption maxima at 271 and 275 nm, respectively (4). The cinnamic acids absorb in two regions in the ultraviolet, one... 

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