Polyphenol oxidase enzymes

FIa.VOnoIOxida.tlon, The fermentation process is initiated by the oxidation of catechins (1) to reactive catechin quinones (13), a process catalyzed by the enzyme polyphenol oxidase (PPO) (56). Whereas the gaHocatechins, epigaHocatechin, and epigaHocatechin gaHate, are preferred, polyphenol oxidase can use any catechin (Table 2) as a substrate. This reaction is energy-dependent and is the basis of the series of reactions between flavanoids that form the complex polyphenoHc constituents found in black and oolong teas. 

The products of oxidation are easily visualized shortly after ozone treatments but no claim should be made that phenolics or the oxidative enzymes, polyphenol oxidase, phenolase or peroxidase... 

Phenols are present in chloroplasts (23, 24) and in vacuoles (25) of plant cells. The enzyme polyphenol oxidase and other enzymes of the phenolase complex are bound to the chloroplast lamellae or stroma 27) and in the cytoplasm (26). Although... 

Wastewater and dying effluent generated by textile and other industries are generally discharged to the surrounding environment without any further treatment. These pollutants apart from adding color to water also cause toxicity to aquatic and other forms of life (Khan and Husain, 2007). Immobilized potato enzyme polyphenol oxidase (celite bound) has been reported to be... 

Table II gives the results of residual trypsin inhibitor levels for the various soymilk preparations. The 90 and 120 sec microwave treatments were the most effective in inactivating the trypsin inhibitor complex while hot water treated and unheated samples showed the highest levels. It is not surprising to find that microwave processing is more efficient than hot water in suppressing trypsin inhibitor considering the rapid penetration of food material by microwaves and the susceptibility of protein action to small heat induced changes in tertiary structure. Hence, Collins and McCarty (12) found microwaves produced a more rapid destruction of endogenous potato enzymes (polyphenol oxidase and peroxidase) than hot water heating.

SCFs offer a nonaqueous environment which can be desirable for enzymatic catalysis of lipophilic substrates. The lipophilic substance cholesterol is 2 to 3 orders of magnitude more soluble in CX>2-cosolvent blends than in waterQ). In CO2 based blends, it may be oxidized to cholest-4en-3one, a precursor for pharmaceutical production using an immobilized enzyim(22). The enzyme polyphenol oxidase has been found to be catalytically active in supercritical CO2 and fluoroform (22). The purpose of using a SCF is that it is miscible with one of the reactants-oxygen. Lipase may be used to catalyze the hydrolysis and interesterification of triglycerides in supercritical OO2 without severe loss of activity(24). These reactions could be integrated with SCF separations for product recovery. 

In lettuce, raised CO2 atmospheres may cause a disorder called brown stain (browning of the epidermal tissue). This is caused by the production of brown pigments generated by the oxidation of phenolic compounds in the presence of the enzyme polyphenol oxidase. It was reported that under high CO2 atmospheres, PAL activity was induced whereas phenolic production and browning were inhibited until the lettuce was transferred from CO2 to air [164 165]. After this transfer, tissue browning occurred, which was associated with a rapid increase in the soluble phenolics content. 

Using the techniques developed to synthesize the organometallic-based SAP catalysts, several enzyme-based SAP catalyst, using porous glass beads and the enzymes polyphenol oxidase and horseradish peroxidase have been studied [53]. These SAP catalysts were active in the reaction of phenol with O2 or H2O2, respectively. Thus, porous enzyme-based SAP catalysts can be synthesized. 

If you put lemon juice on your fruit after cutting it to prevent browning, this is an example of that last category of preservative—one that slows some enzymatic process. The vifcimin C lowers the pH (because it is an acid), slowing the enzymes (polyphenol oxidases emd tyrosinases) that cause browning of your fruit. 

Some experiments report on the realization of amperometric biosensors based on alumina sol-gel matrices (Liu, 1999, 2000a, 2000b). Alumina is formed via the hydrolysis of aluminium aUcoxides Al(OPr )3 and heated around 90°C to give a boehmite sol (y-AlOOH). This sol can be mixed with an aqueous suspension of enzyme and deposited onto an electrode (Liu, 1999). The pore size can be easily controlled by changing the AI/H2O ratio allowing the encapsulation of molecules of different sizes. Amperometric tyrosinase biosensors for instance were made in which the enzyme (polyphenol oxidase) is trapped in a matrix with large pores whereas smaller pores are formed to trap the [Fe(CN)6] ] mediator (Liu, 2000a). 

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