Polyphenols phenolic acids

Recognized subjectively for sourness, cranberries have this flavor profile because of their richness in a variety of polyphenols (phenolic acids), which increase the acidity of the fruit. This characteristic is also the most probable health factor in cranberries, as phenolic acids may be... 

Nucleic acids (RNA) Polyphenols, phenolic acids Iso-flavones (oestrogens) Artefact amino-acids... 

Various phenolic acids have been reported to inhibit IAA oxidase (9, 52,120), and other phenols may act as cofactors of IAA oxidase (144). In general, the cofactors of IAA oxidase are monophenols, whereas the inhibitors of the system are polyphenols, with o-dihy-droxyphenols being the most inhibitory (52, 65). Unsaturated lactones have also been reported to inhibit IAA oxidase (2, 52). 

Phenolic acids and polyphenols are natural plant constituents which impart flavor and textural components to beverages made from these plants. In order to better understand the role of these easily oxidized compounds in the flavor and stability of beverages, it is necessary to determine them at the low concentrations they occur. LCEC has been shown to be quite effective at these trace determinations... 

Males et al. [103] used aqueous mobile phase with formic acid for the separation of flavonoids and phenolic acids in the extract of Sambuci flos. In a cited paper, authors listed ten mobile phases with addition of acids used by other investigators for chromatography of polyphenolic material. For micropreparative separation and isolation of antraquinone derivatives (aloine and aloeemodine) from the hardened sap of aloe (Liliaceae family), Wawrzynowicz et al. used 0.5-mm silica precoated plates and isopropanol-methanol-acetic acid as the mobile phase [104]. The addition of small amounts of acid to the mobile phase suppressed the dissociation of acidic groups (phenolic, carboxylic) and thus prevented band diffusions. 

The sugars attached to the anthocyanin molecule are in order of relative abundance glucose, rhamnose, galactose, xylose, arabinose, and glucuronic acid. The molecule may also contain one or more of the acyl acids p-coumaric, caffeic, and ferulic or the aliphatic acids malonic and acetic esterified to the sugar molecules. Extracts of anthocyanins invariably contain flavonoids, phenolic acids, catechins and polyphenols. The net result is that it is impossible to express the chemical composition accurately. Specifications usually present tinctorial power, acidity, per cent solids, per cent ash and other physical properties. 

Konishi, Y., Kobayashi, S., and Shimizu, M., Tea polyphenols inhibit the transport of dietary phenolic acids mediated by the monocarboxylic acid transporter (MCT) in intestinal Caco-2 cell monolayers, J. Agric. Food Chem., 51, 7296, 2003. 

In addition to vitamins and minerals, tubers contain a complex assortment of other small molecules, many of which are phytonutrients. These include polyphenols, flavonols, antho-cyanins, phenolic acids, carotenoids, polyamines, glycoalkaloids, tocopherols, calystegines, and sesquiterpenes. 

Polyphenols constitute one of the most and widely distributed groups of substances in the plant kingdom, with more than 8000 phenolic structures currently known. They can be divided into at least 10 different classes based upon their chemical structure, ranging from simple molecules, such as phenolic acids, to highly polymerized compounds, such as tannins. 

Polyphenols can act as antioxidants by a number of potential pathways. The most important is likely to be by free radical scavenging, in which the polyphenol can break the radical chain reaction. Polyphenols are effective antioxidants in a wide range of chemical oxidation systems, being capable of scavenging peroxyl radicals, alkyl peroxyl radicals, superoxide, hydroxyl radicals, nitric oxide and peroxynitrate in aqueous and organic environments [121]. This activity is due to the ability of donating an H atom from an aromatic hydroxyl group to a free radical, and the major ability of an aromatic structure to support an unpaired electron by delocalization around the 7i-electron system. Phenolic acids... 

Phase inversion, in emulsions, 602 Phenolic acids, see also Polyphenolics Phenolics. see Polyphenolics Phenol-sulfuric acid assay, carbohydrates, 653-655, 658-659 Phenylalanine... 

Phenolic acids Tannins Polyphenol oxidase, see Diphenol oxidases Polysaccharides cell wall... 

In this protocol, polyphenolics are fractionated into neutral and acidic fractions to prevent interference among polyphenolics in HPLC analysis. Phenolic acids are completely ionized at pH 7.0 and un-ionized at pH 2.0. This property allows for fractionation of neutral polyphenolics at pH 7.0 and acidic polyphenolics at pH 2.0. Two individually preconditioned Cl8 cartridges, one for neutral polyphenolics and the other for acidic polyphenolics, are used for this separation (Figure 11.2.2). 

Polyphenolics are classified into three important groups phenolic acids, flavonoids, and tannins. Phenolic acids include hydroxyben-zoic (C6-Ci), hydroxyphenylacetic (C6-C2), and hydroxycinnamic (C6-C3) acids (Figure 11.2.3 also see Figure 11.3.3). Hydroxycinnamic acids are most widely distributed in plant tissues. The important hydroxycinnamic acids are p-coumaric, caffeic, ferulic, and sinapic... 

Retention times of the peaks are subject to the particular type of column. The acidic fraction from solid-phase extraction consists of phenolic acids such as cis-coutaric, trans-coutaric, and trans-caftaric acids. Isocratic elution is suitable because of the limited number of compounds found in the acidic fraction. Analysis of the acidic fraction is completed within 30 min. See Figure 11.3.1 for an HPLC chromatogram of the acidic polyphenolics isolated from Niagara grapes. 

Figure 11.3.11 Sample UV spectra from various polyphenolics classes (A) cinnamic acid (a phenolic acid), (B) cyanidin (an anthocyanidin), (C) catechin (a flavan-3-ol), and (D) quercetin (a flavonol). AU, absorbance units.

The determination of polyphenolics may result in interference due to co-elution of phenolic acids and procyanidins. This problem can be eliminated by fractionation of polyphenolics into acidic and neutral polyphenolics prior to sample injection into the HPLC system. Because the fractionation techniques effectively improve the resolution of many polyphenolic peaks in the reversed-phase HPLC system, it is suggested that further characterization and identification of unknown peaks be conducted by additional methods such as mass spectrometry and nuclear magnetic resonance. 

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