Potato polyphenol oxidase

Henderson HM, Eskin NAM, Pinsky C, et al. 1992. Pyridine and other coal tar constituents as inhibitors of potato polyphenol oxidase A non-animal model for neurochemical studies. Life Sci 51 207-210. 

Munshi, C. B., and Mondy, N. I. (1988). Effect of soil applications of sodium molybdate on the quality of potatoes polyphenol oxidase activity, enzymatic discoloration, phenol and ascorbic acid. J. Agric. Food Chem. 36 919-22. 

Oxidations now known to be catalyzed by copper-containing enzymes were noticed over a century ago, when Schoenbein observed that oxidation of natural substrates resulted in pigment formation in mushrooms. Individual enzymes were gradually identified laccase by Yoshida in 1883 and tyrosinase by Bertrand in 1896. However, it was not imtil potato polyphenol oxidase was isolated in 1937 by Kubowitz that the role of copper was defined. The family of copper oxidases includes a number of enzymes of both plant and animal origin that may very probably be found to react through similar mechanisms, but which exhibit a number of individual characteristics. The enzymes to be described in this section include potato phenol oxidase, mushroom polyphenol oxidase (tyrosinase), laccase, mammalian and insect tyrosinase, and ascorbic acid oxidase. Each of these differs in certain respects from the others, and undoubtedly other related enzymes will be described from other sources that resemble these, but also display individualities. In these cases, identities in nomenclature must not be extended to imply identities in enzyme structure or activity. 

Because yams are stored in open systems at ambient temperatures (usually warm), tuber tissue was examined for proteinase activity at 40°C. Some tubers had high apparent polyphenol oxidase activity upon peeling of the tubers (tissue turned deep purple at the peeled surface) so that PYP was added to extracts to combine with polyphenolic compounds and protect the proteinase from reacting with these compounds. Earlier studies had shown some inhibition of alkaline proteinase activity by ferric ion (24) so that EDTA was also added to the extracts to chelate any free iron. Two alkaline pH optima were found, at 9.0 and 10.5. The alkaline proteinases of white potatoes (Solanum tuberosum) have pH optima between 8.6 and 9 (25) and those of Carilla chocola tubers have pH optima between 8.0 and 9.5 (26,27T, suggesting that alkaline... 

Friedman, M., Bautista, F. F. (1995). Inhibition of polyphenol oxidase by thiols in the absence and presence of potato tissue suspensions. J. Agric. Food Chem., 43, 69-76. 

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... 

Khan, A. A., Husain, Q. (2007). Decolorization and removal of textile and non-textile dyes from polluted waste-water and dyeing effluent by using potato (Solanum tuberosum) soluble and immobilized polyphenol oxidase. 

In the authors experience, the pigments of a wide variety of plant materials have been stable in the aqueous acetone extract. However, problems have been encountered with pigment degradation for certain potato cultivars with high polyphenol oxidase activity. This problem can be circumvented by putting the aqueous acetone extract (uncapped) in a boiling water bath for 5 min. After heating, the volume of acetone lost by evaporation should be replenished. This enzyme inactivation step has been found unnecessary for most materials. 

The browning offruitisa common example of the oxidation of phenols to quinones. Apples, pears, potatoes, etc. contain polyphenol oxidase (PPO), an enzyme that catalyzes the oxidation of naturally occurring derivatives of catechol (benzene-1,2-diol) by atmospheric oxygen. The products are ortho-quinones, which are unstable and quickly condense to give brown polymers. 

Polyphenol Oxidases. Plant trichomes and their exudates confer resistance to a variety of insects (54-56). In solanaceous plants, such as the tomato and potato, trichomes contain polyphenol oxidases and catecholic phenolics (e.g., caffeic and chlorogenic acids), which contribute to resistance to a variety of insect pests. In the potato plant, the polyphenol oxidases and phenolics are separated in different trichomes. When insects, such as aphids or leaf hoppers, walk across the surface of the plant they break the two types of trichomes. Trichomal fluids are liberated and, upon mixing, polymerize as a result of polyphenol oxidase activity on catechols, forming an often lethal adhesive trap for the insects (52,58) In tomato plants, the polyphenol oxidase and chlorogenic acid are separated by intracellular compartments, but upon breakage of trichomes by insects, polymerization and physical entrapment occurs (54). 

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.

Polyphenol oxidase Mushroom, grape, pear, kiwi, sago, tea, potato, strawberry, olive, beet, cocoa Enzymatic browning (pig-ments),ripening of fruits, flavour formation, colour e.g. strawberries) formation... 

Enzymes other than peroxidase and catalase have been used less frequently to monitor adequacy of heat treatment. Some enzymes that have been used include polyphenol oxidase for off-color development in fruits, polygalacturonase for loss of consistency in tomatoes, potatoes and eggplants and lipoxygenase and lipase for... 

The following experiments illustrate that when studying the involvement of phospholipase in the host-pathogen interaction, the total contribution of enzyme of host origin may be considerably higher than previously realized. Rodionov and Zakharova (32) recently reported very high rates of autolytic hydrolysis of membrane lipids in homogenates of potato leaves (26-37% of the phospholipids were hydrolyzed after 2 h at 0-1 ). Our laboratory recently confirmed this observation and proceeded to study sosie of the properties of the lipolytic acyl hydrolase activity in potato leaves (6). Lipolytic acyl hydrolase activity is apparently inactivated by polyphenol oxidase or its toxic quinone products. 

When polyphenol oxidase activity was controlled, phospholipase activities ranged from 1.04 to 11.60 J mol/min/gfw in the leaves of 41 North American cultivars (6). These values are much higher than those previously reported for potato leaves (.009 pmol/min/gfw)... 

Potato (5. tuberosum) slices (polyphenol oxidase inhibition)... 

Ma, S.X. et al. Prevention of enzymatic darkening in frozen sweet potatoes [Ipomoea batatas (L.) Lam.] by water blanching Relationship among darkening, phenols, and polyphenol oxidase activity, J. Aerie. Food Chem., 40, 864, 1992. 

Enzymatic polymerization of soluble lignin fragments (lignin oligomer) was demonstrated. In the polymerization catalyzed by HRP, or polyphenol oxidase (potato), brown precipitates were formed (286). The increase of the molecular weight was observed in the laccase-catalyzed treatment of the lignin oligomer (287). 

Laccase. A polyphenol oxidase has been purified from the sap of the lac tree by Keilin and Mann. Laccase differs from the potato and mushroom enzyme in several respects. With regard to substrate specificity, it oxidizes p-phenylenediamine more rapidly than catechol. p-Phenylene-diamine is not a substrate for the other polyphenol oxidases described. Laccase apparently is inert with p-cresol. It is not inhibited by carbon monoxide. Unlike the other phenol oxidases, this enzyme is not a pale yellow, but is blue, as is ascorbic acid oxidase (see below). This enzyme, however, is not an ascorbic acid oxidase. 

Coetzer C, Corsini D, Love S, Pavek J, Turner N. Control of enzymatic browning in potato (Solanum tuberosum L) by sense and antisense RNA from tomato polyphenol oxidase. J Agric Food Chem 2001 49 652-657. 

Polyphenol oxidases and ascorbic acid oxidase, which occur in food, are known to have a Cu /Cu redox system as a prosthetic group. Polyphenol oxidases play an important role in the quality of food of plant origin because they cause the enzymatic browning for example in potatoes, apples and mushrooms. Tyrosinases, catecholases, phenolases or cresolases are enzymes that react with oxygen and a large range of mono and diphenols. 

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