Phenols with polyphenol oxidase

Plant susceptibility to ozone as determined by visible injury may be very closely related to quantities of o-diphenols associated with the chloroplasts and specific requirements for activation of polyphenol oxidase enzymes. There is a significant correlation between ozone injury and concentrations of total phenols expressed as percent caffeic acid equivalents in peanut cultivars. This concept is not intended to underestimate the importance of membranes that separate phenols and enzymes. Perhaps future research will demonstrate that membranes of resistant alfalfa, green bean and other species differ both qualitatively and quantitatively from those of susceptible plants of these species. 

The phenol oxidases probably play no important role in the elimination of phenolic pressor amines, in spite of the importance that has been attached to the oxidation of the catechol nucleus in the past. The names phenolase and cresolase, polyphenol oxidase, and catechol oxidase serve to identify the enzyme with its mono- or diphenolic substrate, but they usually occur together and are difficultly separated. The enzymes have been purified and their characteristics have been described (56, 104, 106, 156). Beyer (21), Alles (5), and Randall and Hitchings (129) have described the relationship of structure of the phenolic pressor amines to the rate of oxidation of their nucleus in the presence of these enzymes. 

To construct and apply a biosensor based on capric acid/graphite powder modified with crude extract of jack fruit (Artocarpus integrifolia L.) as the source of polyphenol oxidase to determine total phenols in wastewaters by differential pulse voltammetry (DPV). 

Figure 7 Activation of phenolics by oxidative enzymes such as polyphenol oxidases (PPO) and peroxidases (POD) and reaction of activated phenolics with protein.

Ascorbic acid browning is also inhibited by the addition of sulfite (Wedzicha and McWeeny, 1974). The same holds for polyphenol oxidase-catalyzed oxidation of natural phenols in fruit. The mechanism of the inhibition is by reaction of oquinone intermediates with sulfite, which leads to nonreactive sulfocatechols (Wedzicha, 1995). 

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