Proanthocyanidins and

Polyphenols are significant constituents in the IDF of the samples analyzed, accounting for 1.4% to 4.7% (average, 2.5%). PPs are therefore an important constituent of DF in fruits and vegetables they are mainly condensed tannins (proanthocyanidins) and hydrolyzable tannins. 

Sun B, Spranger MI (2005) Review quantitative extraction and analysis of grape and wine proanthocyanidins and stilbenes. Ciencia Tec Vitiv 20 59-89... 

Flavan-3-ols (catechins, proanthocyanidins, and condensed tannins) can often be extracted directly with water. However, the composition of the extract does vary with the solvent — whether water, methanol, ethanol, acetone, or ethyl acetate. For example, it is claimed that methanol is the best solvent for catechins and 70% acetone for procyanidins. ... 

Drewes, S.E. and Taylor, C.W., Methylated A-type proanthocyanidins and related metabolites from Cassipourea gwnmiflua. Phytochemistry, 31, 551, 1994. 

Ramirez-Coronel, M.A. et al.. Characterization and estimation of proanthocyanidins and other phenolics in coffee pulp (Coffea arabica) by thiolysis-high-performance liquid chromatography, J. Agric. Food Chem., 52, 1344, 2004. 

Santos-Buelga, C. and Scalbert, A., Proanthocyanidins and tannin-like compounds — nature, occurrence, dietary intake and effects on nutrition and health, J. Sci. Food Agric., 80, 1094, 2000. 

Acid-catalyzed cleavage of proanthocyanidins and methylmethine-linked species, generating flavanol carbocations and vinylflavanols, respectively. 

Cheynier, V. and Fulcrand, H., Analysis of proanthocyanidins and complex polyphenols. In Methods in Polyphenol Analysis (eds C. Santos-Buelga and G. Williamson), Royal Society of Chemistry, London, 2003, p. 282. 

Investigations of the conformational properties of the flavan-3-ols and oligomeric proanthocyanidins have hitherto involved a variety of molecular mechanics and molecular orbital computations in combination with crystal structures, time-resolved fluorescence, as well as and NMR methods. Representative references to all these techniques may be found in the papers listed in Refs. 241-247, 250. These NMR papers incidentally also represent the major contributions regarding the conformation of proanthocyanidins, and may be summarized in a conformational context by reference to the significant contributions of Hatano and Hemingway. 

Cui, C.B. et al., Constituents of a fern, Davallia mariesii Moore. V. Isolation and structure of davallin, a new tetrameric proanthocyanidin, and two new phenolic glycosides, Chem. Pharm. Bull, 41, 1491, 1993. 

Proanthocyanidins and Procyanidins - In a classical study Bate-Smith ( ) used the patterns of distribution of the three principal classes of phenolic metabolites, which are found in the leaves of plants, as a basis for classification. The biosynthesis of these phenols - (i) proanthocyanidins (ii) glycosylated flavonols and (iii) hydroxycinnamoyl esters - is believed to be associated with the development in plants of the capacity to synthesise the structural polymer lignin by the diversion from protein synthesis of the amino-acids L-phenylalanine and L-tyro-sine. Vascular plants thus employ one or more of the p-hydroxy-cinnarayl alcohols (2,3, and 4), which are derived by enzymic reduction (NADH) of the coenzyme A esters of the corresponding hydroxycinnamic acids, as precursors to lignin. The same coenzyme A esters also form the points of biosynthetic departure for the three groups of phenolic metabolites (i, ii, iii), Figure 1. 

Comparative Aspects of Polyphenol Metabolism - Proanthocyanidins and the complex esters of gallic and hexahydroxydiphenic acid show many structural similarities as plant metaijol i tes. The shape and size of the ester (5) is thus very similar to that of a proanthocyanidin hexamer (1, n = 4). The most striking feature of both structures however s the manner in which free phenolic groups are distributed over the surface of the molecule providing a structure with the inbuilt capacity for multidentate attachment to other species by hydrogen bonding. 

Proanthocyanidins are polymeric flavonoid compounds composed of flavan-3-ol subunits (unitii.3), and are responsible for bitterness and astringency in some foods and beverages. This unit describes methods for extracting and purifying proanthocyanidins, and for determining their subunit composition by HPLC. Based upon HPLC results, the average degree of polymerization and the conversion yield for purified proanthocyanidins can be determined. 

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. 

Weigh the proanthocyanidins and calculate recovery in mg proanthocyanidins/kg sample (see Basic Protocol 1, step 1). 

Hemingway, R.W. 1989a. Structural variations in proanthocyanidins and their derivatives. In Chemistry and Significance of Condensed Tannins (R.W. Hemingway and J.J. Karchesy, eds.) pp. 83-108. Plenum Press, New York. 

D Madigan, I McMurrough, MR Smyth. Determination of proanthocyanidins and catechins in beer and barley by high-performance liquid chromatography with dual-electrode electrochemical detection. Analyst 119 863-868, 1994. 

Main actives Purine alkaloids - mainly caffeine (0.6-3.7%) with some theophylline and theobromine, tannins, proanthocyanidins and 45% starch. 

A third method relies on the precipitation of proanthocyanidins with formaldehyde. First, the total phenolic content is measured using the Folin-Ciocalteu reagent as described before. A 0.5 mole equivalent of phloroglucinol (1.3) is added for every gallic acid equivalent in the extract. To 2 mL of this plant extract and phloroglucinol is added 1 mL of a 2 5 HC1 /H20 solution and 1 mL of an aqueous solution of formaldehyde (13 mL of 37% formaldehyde diluted to 100 mL in water). After an overnight incubation at room temperature, the unprecipitated phenols are estimated in the supematent by the Folin-Ciocalteu method. The precipitate contains the proanthocyanidins and the known amount of phloroglucinol, which is always quantitatively precipitated. 

Phenolic compounds and flavonoids are a unique category of plant phytochemicals especially in terms of their vast po ential health-benefiting properties. They represent the most abundant and the most widely represented class of plant natural products. A substantial amount of research has been carried out over the past two decades yet large information gaps still exist. For example, the inventory of these compounds is still incomplete, although there is continuous effort to provide new structures. In addition the dissection of the metabolic pathways for certain phenolic compounds remains to be resolved. Recent reports underline that important questions that still need to be answered in the field of proanthocyanidin and tannin biosynthesis [Xie and Dixon, 2005], and even the exact nature of the biosynthetic pathway(s) leading to lignin monomers is not fully elucidated. 

Li H, Flachowsky H, Fischer T, Hanke M-V, Forkmann G, Treutter D, Schwab W, Hoffmann T, Szankowski I. 2007. Maize Lc transcription factor enhances biosynthesis of anthocyanins, distinct proanthocyanidins and phenylpropanoids in apple (Malus domestica Borkh.) Planta 226 1243-1254. 

Tian L, Pang Y, Dixon RA. 2008. Biosynthesis and genetic engineering of proanthocyanidins and (iso)flavonoids. Phytochem Rev 7 445-465. 

Jaakola L, Maatta K, Pirttila AM, Torronen R, Karenlampi S, Hohtola A. 2002. Expression of genes involved in anthocyanin biosynthesis in relation to anthocyanin, proanthocyanidin, and flavonol levels during bilberry fruit development. Plant Physiol 130 729-739. 

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