Polyphenol, oxidation

In the production of opalescent or natural-type apple juice, ascorbic acid is added to the fmit pulp before pressing, or to the juice as it comes from the press, to retain more of the apple flavor (4). Ascorbic acid addition and pasteurization of the juice as soon as possible after pressing prevent polyphenol oxidation, which causes browning and contributes to pulp flocculation. 

Hutcheson SW, Buchanan BB. Polyphenol oxidation by Viciafaba chloroplast membranes studies on the latent membrane-bound polyphenol oxidase and on the mechanism of photochemical polyphenol oxidation. Plant Physiol 1966 66 1150-1154. 

Makhotkina, O. and Kilmartin, P. A. (2009). Uncovering the influence of antioxidants on polyphenol oxidation in wines using an electrochemical method Cyclic voltammetry. J. Electroanal. Ghem. 633,165-174. 

Green tea is made by steaming or frying fresh tea leaves at elevated temperatures to prevent polyphenol oxidation. The chemical composition of green tea is similar to that of the fresh leaves regarding the major components. It contains polyphenols, which include flavanols, flavandiols, flavonoids, and phenolic acids. Flavanols are the most abundant constituents and are commonly known as catechins. The major catechins present in green tea are (-)-epicatechin (EC), (-)-epicatechin-3-gallate... 

The lag time effect probably results from the inhibition of copper-containing oxidases and other copper-catalyzed oxidative processes in apple by Sporix. These oxidative reactions normally would bring about the rapid loss of AA and permit browning to occur once the added AA was depleted (18). Sporix also would inhibit PPO directly by chelation of its copper (3), thereby decreasing the rate of polyphenol oxidation and subsequent browning. The ability of Sporix to exert its effect on enzymatic browning by these two independent mechanisms probably accounts for the apparent synergism obtained with Sporix-AA combinations. 

Green tea and black tea are produced using different processing methods for tea leaves of Camellia sinensis. Green tea is produced by drying the leaves of Camellia sinensis at elevated temperatures to prevent polyphenol oxidation. The major... 

The relation between oxidation of monophenols and polyphenols has been investigated extensively by Nelson and his students. The nature of the reactions studied is still not clear, but many interesting aspects have been explored. As in the case of other workers, it was found that there is a tendency for the ability to oxidize monophenols (cresolase) to be lost on purification, while polyphenol oxidation (catecholase) is more stable. The ratio of catecholase to cresolase activity of purified preparations appears to vary with electrophoretic mobility, and it has been suggested that a peptide component is lost from the enzyme, and that the purified preparations represent partially degraded enzyme. ... 

Feldman, K.S., Sambandam, A., Bowers, K.E. Appel, H.M. (1999b). Probing the role of polyphenol oxidation in mediating insect-pathogen interactions. Galloyl-derived electrophilic traps for the Lymantria dispar nuclear polyhedrosis virus matrix protein polyhedrin. The Journal of Organic Chemistry, 64, 5794-5803. 

Scampicchio, M., Bulbarello, A., Arecchi, A., and Mannino, S. (2008) Electrospun nanofibers as selective barrier to the electrochemical polyphenol oxidation. Elec-trochem. Commun., 10, 991-994. 

The blends are aged in 5-6 hi oak barrels (pipas) for several years in oxidative conditions that maintain an elevated oxidation-reduction potential. Metal ions, in particular copper and iron, play an essential role in polyphenol oxidation. Even in the bottle, these wines conserve a high oxidation-reduction potential. The iron remains in its ferric state, as if all of the reducing components had been destroyed by oxygen. Their prolonged oxidation and intense esterification give these wines a rich and complex bouquet. 

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