Phenols/polyphenols solvent

Polyphenols. Another increa singly important example of the chemical stabilization process is the production of phenoHc foams (59—62) by cross-linking polyphenols (resoles and novolacs) (see Phenolic resins). The principal features of phenoHc foams are low flammabiUty, solvent resistance, and excellent dimensional stabiUty over a wide temperature range (59), so that they are good thermal iasulating materials. 

Polyphenols are ubiquitous in all plant organs where they are found as monomers or in polymerised forms (Schofield et al, 2001). In addition to the beneficial effect of poljq)henols, they also bind minerals and precipitate proteins and carbohydrates, in effect reducing the nutritive value of foods. Polyphenols have been classified for nutritional purposes into extractable and non-extractable types (Bravo, 1998). Extractable polyphenols are low-and intermediate-weight phenolics while non-extractable polyphenols have high molecular weight and are insoluble in normal solvents. 

Dissociation of the Protein-Poly phenolic Complex and Characterization of the Polyphenolic Fraction. Since Indulin ATR is almost completely soluble in THF while the APPL s are quite insoluble in this solvent, but are soluble in DMF, a sequence of different percentage mixtures of these two solvents was used in order to dissociate the protein-lignin complexes for further analyses of the lignin part. 

For an accurate quantification of phenolic compounds extracted from plant material, the starting plant material should be washed, dried, and weighed prior to extraction, and the amount of the final extract should be recorded. The extracted polyphenolics are generally diluted and then concentrated by evaporation of solvents. Evaporation should be performed at 30° to 40°C under reduced pressure. When extract-... 

An accurate sample weight before extraction and the amount of final extract after sample cleanup should be known for an accurate quantification of phenolic compounds extracted from plant materials by HPLC analysis. The characteristic wavelengths for detection of polyphenolics can be selected at the discretion of the experimenter. The solvent gradients described in the Basic and Alternate Protocols can be modified for better resolution. 

For phenolics in fruit by-products such as apple seed, peel, cortex, and pomace, an HPLC method was also utilized. Apple waste is considered a potential source of specialty chemicals (58,62), and its quantitative polyphenol profile may be useful in apple cultivars for classification and identification. Chlorogenic acid and coumaroylquinic acids and phloridzin are known to be major phenolics in apple juice (53). However, in contrast to apple polyphenolics, HPLC with a 70% aqueous acetone extract of apple seeds showed that phloridzin alone accounts for ca. 75% of the total apple seed polyphenolics (62). Besides phloridzin, 13 other phenolics were identified by gradient HPLC/PDA on LiChrospher 100 RP-18 from apple seed (62). The HPLC technique was also able to provide polyphenol profiles in the peel and cortex of the apple to be used to characterize apple cultivars by multivariate statistical techniques (63). Phenolic compounds in the epidermis zone, parenchyma zone, core zone, and seeds of French cider apple varieties are also determined by HPLC (56). Three successive solvent extractions (hexane, methanol, aqueous acetone), binary HPLC gradient using (a) aqueous acetic acid, 2.5%, v/v, and (b) acetonitrile fol-... 

The gluing experiments were done with commercially available starch, proteins (casein, glutin) and tannins of mimosa Acacia spp.), Pinus radiatay and quebracho (Schinopsis spp.) and with tannins extracted from the bark of spruce (Picea abies) and common pine (Pinus sylvestris). The extractions were carried out with water or organic solvents under alkali and/or sulphite conditions on a laboratory scale aiming at optimization of yield and polyphenolic extract content. After extraction, the solutions were concentrated under reduced pressure and freeze dried. One pine bark extract was modified with phenol. A summary of the tannin extracts and their properties is given in Table I. 

The morphology of the enzymatically synthesized polyphenols was controlled under the selected reaction conditions. HRP-catalyzed dispersion polymerization of phenol in a mixture of 1,4-dioxane and phosphate buffer using poly(vinyl methyl ether) as stabilizer produced monodisperse polyphenol particles in the submicrometer range.19 m-Cresol and p-phenylphenol were also converted to the polyphenol particles by the dispersion polymerization. The particle size could be controlled by the stabilizer concentration and solvent composition. Thermal treatment of these particles afforded uniform carbon particles. 

Peroxidase-catalyzed grafting of polyphenols on lignin was performed by HRP-catalyzed polymerization of />cresol with lignin in the aqueous 1,4-dioxane or reverse micellar system.57 Phenol moiety in lignin was reacted with />cresol to produce a lignin—phenol copolymer with a branched and/or cross-linked structure. The product was highly insoluble in common organic solvents. 

Oxidation of a number of p-substituted phenols to the corresponding o-benzoquinones was first performed by Kazandjian and Klibanov, using mushroom polyphenol oxidase and a quantitative conversion was achieved in CHCI3 as a solvent. Other hydrophobic solvents such as methylene chloride, carbon tetrachloride, benzene, toluene, hexane and butyl acetate can be used, whereas the enzyme is inactive in more hydrophilic solvents such as ether, acetone, ethyl acetate, acetonitrile and other solvents. In addition, an immobilized enzyme on glass powder or beads is more efficient than a free enzyme. 

The rather simple solvent classification schemes yield complex fractions of botanochemicals. Their detailed composition depends not only on the species but also on maturity of the plant and the method of extraction (1 5, ). The polar fraction isolated by acetone extraction and readily soluble in 87.5% aqueous ethanol, termed "polyphenol" by Buchanan and coworkers (11,12), no doubt consists of phenolics and a wide variety of other substances. For plants of high tannin content, (e.g., Rhus g/aubra) the polyphenol fraction might well be called tannin (24)... 

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