Effect of polyphenol oxidase

FIGURE 8.10 Scheme of the possible formation mechanism of thearubigins. (From Finger, A. 1994. In-vitro studies on the effect of polyphenol oxidase and peroxidase on the formation of polyphenolic black tea constituents. J. Sci. FoodAgric. 66 293-305. With permission.)... 

Since the chlorogenic acid content was reported to be higher in inner (younger) than in outer bracts, the blackening which is caused by the effect of polyphenol oxidase on ortho-di-phenols is much greater in the inner tissues of the head [39]. 

De Brito ES, Garcia NHP, Amancio AC (2002) Effect of polyphenol oxidase (PPG) and treatments on total phenol and tannin content of cocoa nibs. Ciencia e Tecnol de Aliment, Camp 22 45 ... 

Effects of Polyphenol Oxidase Inhibitor (Piethylthiocarbamate) on Both Mycelial Dry Weight and Extracellular Polyphenol Oxidase... 

Earlier research on phenolic substances in relation to plant disease resistance was concerned not only with the possible protective effects of preformed phenolic compounds, but also whether these compounds are mobilized or their synthesis is promoted at the site of infection. Another aspect which has received attention is that the phenolic compound might be liberated from its glycoside or sugar ester at the Infection site in response to Infection (5J. Chemical changes in Infected tissue due to the activity of polyphenol-oxidases and peroxidases, leading to the production of qulnones and other fungicidal compounds, have also been Investigated (6). 

Xu, J., The effect of low-temperature storage on the activity of polyphenol oxidase in Castanea henryi chestnuts. Postharvest Biol. TechnoL, 38, 91-98, 2005. 

An amperometric biosensor based on immobilization of polyphenol oxidase (PPO) into Zn-Al layered double hydroxides, also called anionic clays, was applied for the determination of cyanide [60]. The detection of cyanide was performed via its inhibiting action on the PPO electrode. Measurement was carried out with 3,4-dihydroxyphenylacetic acid as enzyme substrate, the eirzymatically generated quinoid products being electroreduced at 0.2 V. An extremely sensitive detection limit (0.1 nM) was obtained for cyanide. Enzyme immobilization into anionic exchanger clay seems to cause an increase in cyanide inhibition effects because of anion accumulation in the clay matrix. 

The objectives of this investigation were 1) to ascertain the time-dependent changes in both mycelial dry weight as well as extracellular protein contents in the absence of exogenous polyphenols and 2) to determine the time of appearance of extracellular polyphenol oxidase and addition effects of polyphenols on the oxidase s activity. 

Time of Appearance of Extracellular Polyphenol Oxidase and Addition Effects of Polyphenols on Extracellular Polyphenol Oxidase Activity... 

Immobilization of polyphenol oxidase enzyme in a conducting polymer electrode was studied as an alternative method for determination of phenolic compounds in wines and results reveal that, by considering the inhibitory effects of substances found naturally in wines, this significant development can successfully replace the classical methods. 

Escribano, J., Cabanes, J., and Garcfa-Carmona, R, Characterisation of latent polyphenol oxidase in table beet effect of sodium dodecyl sulphate, J. Sci. Food Agric., 73, 34, 1997. 

Hatano, T. et al., Effects of interactions of tannins with co-existing substances. VII. Inhibitory effects of tannins and related polyphenols on xanthine oxidase, Chem. Pharm. Bull., 38, 1224, 1990. 

To obtain optimum response conditions for the biosensor based on carbon paste modified with polyphenol oxidase of jack fruit (A. in-tegrifolia L.) crude extract, the effect of graphite powder, fatty acids, and the enzyme concentrations were studied. The scan rate, pulse amplitude, and pH were also investigated. Table 23.1 summarizes the range over which each variable was studied and the optimal value found in those studies. 

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