Polyphenol adsorbents

Polyphenol adsorbents are mainly polyamides (Dadic, 1973). At one time various nylons were used, but PVPP is most frequently used today (McMurrough et ah, 1997). The structure of PVPP (see Fig. 2.23) resembles that of polyproline (Fig. 2.6) both have five-membered, saturated, nitrogen-containing rings and amide bonds. 

PolyplasdoneBASF/Divergan size)various (by particle size) adsorbent for polyphenols (tanins), beverage clarification... 

Adsorbents that remove proteins or polyphenols are used to treat a number of beverages to delay the onset of haze formation. Protein adsorbents include bentonite and silica. Bentonite removes protein nonspecifically (see Fig. 2.19) and so is unsuitable for stabilizing beverages where foam is desirable (beer and champagne). Silica, on the other hand, has remarkable specificity for HA proteins while virtually sparing foam-active proteins in beer (Siebert and Lynn, 1997b) (see Fig. 2.20). Silica removes approximately 80% of the HA protein from unstabilized beer, while leaving foam-active protein nearly untouched at commercial treatment levels. 

Siebert, K. J. and Lynn, P. Y. (2008). On the mechanisms of adsorbent interactions with haze-active protein and polyphenol. J. Am. Soc. Brew. Chem. 66, 46-54. 

Ethyl acetate is used on the C18-adsorbed anthocyanins to remove polyphenolic compounds. More efficient polyphenolic recovery will be accomplished if residual water is removed from the cartridge with a nitrogen gas stream for 2 to 3 min before application of ethyl acetate. After washing the column with ethyl acetate, water should not be added because some anthocyanins could be eluted and lost. Ethyl acetate removal of polyphenolics is particularly recommended if the anthocyanin fraction is to be subsequently analyzed by electrospray mass spectroscopy. 

Besides solid-phase extraction, column chromatography is also often used for cleanup and purification of polyphenolics from plant material. Ionic adsorbants (polyvinylpyrrolidone or PVP, polyamides, and Sephadex LH-20) and Amberlite XAD-2 resin have been used to isolate and purify polyphenolics from crude extracts. For the separation of polyphenolics from plant material, column chromatography using Sephadex LH-20, a gel-filtration matrix, is often used with various eluting solvents (Park and Lee, 1996). The most widely used solvents for column chromatography are aqueous methanol and aqueous ethanol. 

Fumed silica A-200 (Pilot plant at the Institute of Surface Chemistry, Kalush, Ukraine specific surface area Ascorbic acid (vitamin C) and all-rac-a-Tocopheryl acetate (vitamin E acetate) were used as adsorbates. Folin-Ciocalteu s phenol reagent (Merck) was used to measure the total polyphenolic index. Silica samples with different degree of surface silylation were obtained using gas-phase chemical modification of highly disperse silica (A-200) surface by trimethylchlorosilane.6... 

Amperometric glucose biosensors based on co-immobiUzation of GOx with [Os(bpy)2(4-VP)ioCl]Cl in electrochemically generated polyphenol film [72]. A bilayer electrode in which Os-pol3nmer is first adsorbed on a Pt electrode and then electrochemically deposited on polyphenol-GOx fihn showed sensitivity of 1.63-1.79 /jA/cm /mM to 20 mM glucose at 0.4 V and 6-7 mM. Low background current and less interference by common electroactive compounds were noted. 

Le Bourvelleca et al. [17] have investigated the sorption of procyanidins, a polyphenol tannin derivative, on native cellulose fibers and other polysaccharide substrates such as modified pectin and xyloglucan and starch. Through this study, they showed a relatively low affinity of the substrate towards the tested chemical which presented a low adsorbed around 4 mg.g. ... 

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