Anthocyanins monomers

Sample Preparation for Analysis of Anthocyanins Monomer in Skins Extract... 

It is also possible to fractionate wine anthocyanins on the basis of their degree of polymerization on a hand-packed column consisting of polyvinyl-polypyrrolidone, silica gel G, and silica 60. The free anthocyanins elute in the first fraction (methanol-HCl 999 1), slightly polymerized anthocyanins in the second fraction (formic acid-water 1 1), and the condensed polymeric forms are eluted in 100% formic acid. The absorbance of the three fractions is read spectrophotometrically (538 nm for the first fraction and 525 nm for the second and third fractions) and their relative proportions may thus be calculated. This test is a very good indicator of the age of a wine the younger the wine the higher the absorbance of the first fraction due to the presence of anthocyanin monomers conversely, the absorbance of the third (polymerized) fraction will be greatest in older wines. 

TOTAL MONOMER (MAF). RED (RPAF) AND YELLOW-BROWN POLYMER (YBPAF) ANTHOCYANIN FRACTIONS OF COMMERCIAL ANTHO-CYANIN-RICH EXTRACTS... 

INDIVIDUAL TOTAL MONOMER (TMA) AND TOTAL ACYLATED MONOMER (TAcMA) ANTHOCYANIN CONTENTS OF COMERCIAL ANTHOCYANIN-RICH EXTRACTS... 

The PAs, or condensed tannins, are polymers synthesized from flavan-3-ol monomer units. The phlobaphenes are 3-deoxy-PAs formed from flavan-4-ol monomers. The biosynthesis of both types of PAs follows the biosynthetic route of anthocyanins from chalcones through to the branch points to flavan-3-ol and flavan-4-ol formation. In this section, the specific enzymes forming the monomers are discussed, along with a discussion on the polymerization process. Although the chemistry of tannins is described in detail elsewhere in this book, it is useful to briefly mention the nature of the monomer subunit types and the polymer forms. 

The phenolics include anthocyanins, anthraquinones, benzofurans, chromones, chromenes, coumarins, flavonoids, isoflavonoids, lignans, phenolic acids, phenylpropanoids, quinones, stilbenes and xanthones. Some phenolics can be very complex in structure through additional substitution or polymerization of simpler entities. Thus xanthones can be prenylated and flavonoids, lignans and other phenolics can be glycosylated. Condensed tannins involve the polymerization of procyaninidin or prodelphinidin monomers and hydrolysable tannins involve gallic acid residues esterified with monosaccharides. As detailed in this review, representatives of some major classes of plant-derived phenolics are potent protein kinase inhibitors. 

The potential impurities will vary according to the plant tissue extracted, and therefore the exact washing volume will vary. It is important to determine the impurities present and their retention properties on the column to minimize impurities in the final proanthocyanidin and maximize proanthocyanidin recovery. For this step, the use of a spectrophotometer is helpful in monitoring the eluate. Some typical impurities and monitoring wavelengths include organic acids (215 nm), flavan-3-ol monomers (280 nm), hydroxycinnamic acids (320 nm), andflavonols (365 nm). Anthocyanins are observable in the visible spectrum. 

The precursors of these reactions are, on one hand, proanthocyanidins and, on the other hand, any kind of flavonoid that can act as a nucleophile. The latter include flavonols, dihydroflavonols, flavanol monomers, proanthocyanidins, and anthocyanins under their hemiketal form (for anthocyanin reactivity, see Chapter 9A). 

Evidence of such adducts in wine fractions has been provided, as detailed in Chapter 9A. These include F-A+ (Alcalde-Eon et al. 2006 Boido et al. 2006) and F-A-A+ (Alcalde-Eon et al. 2006) adducts based on different flavanol and anthocyanin units and (F) -A+ adducts deriving from different flavanols monomers and oligomers (Hayasaka and Kennedy 2003). Proanthocyanidins arising from these reactions cannot be distinguished from those extracted from grapes. However, detection of F-A+ adducts without prior fractionation (Morel-Salmi et al. 2006) confirmed the occurrence of the acid-catalyzed interflavanic bond breaking process in wines. 

Separation of flavans monomer and oligomers from polymers and anthocyanins can be achieved by using a polyamide (1.7g) column (Bourzeix et al., 1986). A volume of 2-10 mL of the sample (wine, seeds or skins extract) is passed through the column, and the more polar... 

To perform analysis of young wines, where anthocyanins are mainly present as monomers, a satisfying HPLC separation can be achieved by direct injection into the column of the sample previously acidified. In... 

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