Proanthocyanidins,

Although earlier reviews by Haslam (134-136) discuss the many problems that have arisen about the systematic classification and nomenclature of proanthocyanidins, it seems useful to repeat the definition of the term proanthocyanidin as initially established by Freudenberg and Weinges (116) - the proanthocyanidins are all the colorless substances isolated from plants which, when treated with acid, form anthocyanidins. Thus the leucoanthocyanidins (now restricted to the flavan-3,4-diols), the condensed tannins (Sect. 7.7), and any other colorless flavonoid derivatives that produce anthocyanidins on heating with acid should be grouped under this class of compounds. 

In comparison, a simplified nomenclature for the flavan-3,4-diols (Fig. 7.6.1, 18 21) is not necessary. The hydroxylation patterns of these compounds are readily recognized from their common names guibourtacacidins (18, 7,4 -dihy-droxy), mollisacacidins (19, 7,3, 4 -trihydroxy), robinetinidins (20, 7,3, 4, 5 -tetra-hydroxy), leucocyanidins (21, 5,7,3, 4 -tetrahydroxy), teracacidins (7,8,4 -trihy-droxy), and melacacidins (7,8,3, 4 -tetrahydroxy). Because only three chiral centers need to be defined, their absolute stereochemistry is readily denoted through use of the Rox S prefix. This is clearly preferable to the use of common names. For example, 2/ ,3S,4/ -mollisacacidin has been variously named (+)-mollisacacidin, (+)-gleditsin and (+)-leucofisetinidin (377). Use of the R and 5 prefix to define the absolute stereochemistry of these compounds avoids the considerable confusion that has occurred with the informal nomenclature used in the past. 

Proanthocyanidins are by far the most common oligomeric flavonoids found in plants (134-136). The low molecular weight oligomers are usually found in low concentration in plant extracts containing the condensed tannins (Sect. 7.7), 

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Proanthocyanidins are an important group of di- to oligomeric flavonoids in plants. Four proanthocyanidins (procyanidin B3, prodelphinidin B4, ECG-(4 8)-ECG and GC-(4 8)-EGCG) were determined quantitatively in tea. The amounts in fresh tea leaves were between 1 and 2 g/kg per compound (Nakabayashi, 1991). The occurrence of proanthocyanidins may serve as a criterion for the differentiation between fermented and non-fermented teas (Kiehne et al, 1997). 

KIEHNE A, LAKENBRINK c and ENGLHARDT u H (1997) Analysis of proanthocyanidins in tea samples , Z Lebensm Unters ForschA, 205, 153-7. 

HOR M, RIMPLER H, HEINRICH M. (1995) Inhibition of intestinal chloride secretion by proanthocyanidins from Guazuma iilmifolia. Planta Med. 61 208-12. 

YAMAKOSHi J, KTAOKA s, KOGA T, ARiGA T (1999) Proanthocyanidin-rich extract from grape seed attenuates the development of aortic atherosclerosis in cholesterol-fed rabbits, Atherosclerosis, 142, 139-49. 

Knowledge of the identity of phenolic compounds in food facilitates the analysis and discussion of potential antioxidant effects. Thus studies of phenolic compounds as antioxidants in food should usually by accompanied by the identification and quantification of the phenols. Reversed-phase HPLC combined with UV-VIS or electrochemical detection is the most common method for quantification of individual flavonoids and phenolic acids in foods (Merken and Beecher, 2000 Mattila and Kumpulainen, 2002), whereas HPLC combined with mass spectrometry has been used for identification of phenolic compounds (Justesen et al, 1998). Normal-phase HPLC combined with mass spectrometry has been used to identify monomeric and dimeric proanthocyanidins (Lazarus et al, 1999). Flavonoids are usually quantified as aglycones by HPLC, and samples containing flavonoid glycosides are therefore hydrolysed before analysis (Nuutila et al, 2002). 

LAZARUS s E, ADAMSON G E, HAMMERSTONE J F and SCHMITZ H H (1999) High-performance liquid chromatography/Mass spectrometry analysis of proanthocyanidins in foods and beverages, JAgric Food Chem, 47, 3693-701. 

Recent scientific investigations of natural polyphenols have demonstrated their powerful antioxidant property (Niki et al, 1995). Several classes of polyphenols have been chemically identified. Some of these are grape polyphenols, tea polyphenols, soy polyphenols, oligomeric proanthocyanidines (OPA) and other natural polyphenols of the flavone class. Rice bran polyphenols are different from the above in that they are p-hydroxy cinnamic acid derivatives such as p-coumaric acid, ferulic acid and p-sinapic acid. Tricin, a flavone derivative, has also been isolated from rice bran. 

Wu, X. et al.. Characterization of anthocyanins and proanthocyanidins in some cul-tivars of Rihes, Aronia and Samhucus and their antioxidant capacity, J. Agric. Food Chem., 52, 7846, 2004. 

When appreciable amounts of pectin, proteins, lipids, unwanted polyphenols, or other compounds are suspected to be present in anthocyanin-containing extracts, some of them can be precipitated or the anthocyanins may be crystalhzed and separated from the others. Pectin and proteins can be removed by organic solvents such as methanol and acetone in order to reduce their solubility, then precipitated and separated by centrifugation. Gelatin was used to remove proanthocyanidin due to its high molecular weight. Anthocyanins were reported to be precipitated early by lead acetate to achieve isolation from other materials. ... 

Thousands of polyphenols from fruits (grapes, apples, etc.), vegetables (horse beans), and teas have been identified, many having good coloring properties, especially anthocyanins and some flavonoids. Well-documented reviews discuss the coloring capacities of some polyphenols including procyanidins. - Detailed presentations of anthocyanin and flavonoid properties and analysis are included in Sections 2.3, 4.3, and 6.3. The soluble proanthocyanidins of the colored horse bean Viciafaba L. seed coats were isolated and separated by solvent partition. 

The chemical characteristics of the proanthocyanidins were elucidated by total oxidation and partial degradation in the presence of phloroglucinol followed by HPLC analysis. The native extract of proanthocyanidins contained (+) gallocatechin, (-) epigallocatechin, (h-) catechin, and (-) epicatechin units. ... 

Nakamura, Y., Tsuji, S., and Tonogai, Y, Analysis of proanthocyanidins in grape seed extracts, health foods and grape seed oils, J. Health Set, 49, 45, 2003. 

Waterhouse et al., A comparison of methods for quantifying oligomeric proanthocyanidins from grape. Am. J. Enol. Vitic., 51, 383, 2000. 

Catechins and Proanthocyanidins Naturally Occurring 0-Heterocycles with Antimicrobial Activity... 

Keywords Antibacterial activity Antimycotic activity Antiprotozoal activity Antiviral activity Cathechins Proanthocyanidins... 

The occurrence in some plants of secondary metabolites characterized by an 0-heterocyclic structure and exhibiting antimicrobial properties is a well-known phenomenon [2,8-10]. Among them, catechins and proanthocyanidins are two classes of compounds exhibiting antimicrobial properties towards both prokaryotic and eukaryotic microorganisms. Yet, despite the large number of studies published so far, the real potentialities and limitations given by the use of this class of molecules as antiviral or antimicrobial (antibacterial, antimycotic, antiprotozoal) agents have not been critically evaluated. The present chapter represents an overview of the re-... 

The B-type procyanidins include a mixture of oligomers and polymers composed of flavan-3-ol units linked mainly through C4 C8 and/or C4 C6 bonds, and represent the dominant class of natural proanthocyanidins. Among the dimers, procyanidins Bl, B2, B3 and B4 (Fig. 2a) are the most frequently occurring in plant tissues. Procyanidin B5 (EC-(4j6 6)-EC), B6 (catechin-(4o 6)-catechin), B7 (EC-(4/3 6)-catechin) and B8 (catechin-(4q 6)-EC) are also widespread (Eig. 2b) [17-19]. 

On the other hand, the flavan-3-ol units can also be doubly linked by an additional ether bond between C2 07 (A-type). Structural variations occurring in proanthocyanidin oligomers may also occur with the formation of a second interflavanoid bond by C-0 oxidative coupling to form A-type oligomers (Fig. 3) [17,20]. Due to the complexity of this conversion, A-type proanthocyanidins are not as frequently encountered in nature compared to the B-type oligomers. 

The A-type proanthocyanidins are characterized by a second ether linkage between an A-ring hydroxyl group of the lower unit and C-2 of the upper unit. Since they are less frequently isolated from plants than the B-types, they have been considered unusual structures [18,19]. The first identified A-type proanthocyanidin was procyanidin A2 isolated from the shells of fruit of Aes-culus hippocastanum. Since then, many more A-type proanthocyanidins have been found in plants, including dimers, trimers, tetramers, pentamers and ethers [18,21]. 

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