Polyphenol oxidase inhibition

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

The most important physical method of polyphenol oxidase inhibition is exposure of the material to higher temperatures. Polyphenol oxidases are inhibited by temperatures above 70 °C, are most stable in media of pH around 6.0, and in both directions from this value their resistance against heating decreases quite sharply. ... 

Pizzocaro F Torreggiani D and Gilardi G. 1993. Inhibition of apple polyphenol oxidase (PPO) by ascorbic acid, citric acid and sodium chloride. J Food Proc Preserv 17 21—30. 

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. 

Besides using the bioactive agent to detect the ion of interest, another approach can include monitoring an ion by its inhibitory effect upon enzymatic activity. For example, horseradish peroxidase (HRP) can be immobilised onto one gate of a REFET [107] allowing the presence of cyanide ion to be measured at concentrations of 10 3-10 7 M. The approach used here is to monitor the inhibition of the enzymatic HRP effect, by the cyanide ion, on ascorbic acid. Even lower levels (10 10 M) of detection can be obtained using a polyphenol oxidase/clay composite immobilised on carbon, with no interference from chloride, nitrate or bromide [108]. 

Janovitz-Klapp A, Richard F, Goupy PM, and Nicolas J. Inhibition studies on apple polyphenol-oxidase. J. Agric. Food Chem. 1990 38 926-931. 

Figure 2.11 HCTA profile of a Chardonnay must sample (a) S02 added and (b) S02 not added, in order to inhibit the polyphenol oxidase (PPO) enzymes. (1) cis-CTA, (2) trans-CTA, (3) czs-p-CuTA, (4) trans-p-CuTA, (5) ds-FTA, (6) trans-YT A, (7) 2-S-glutathionyl caffeyl tartaric acid (GRP)...

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). 

The germination- and growth-inhibiting actions of TCPE, DCPA and 2,4,5-T have been investigated in mustard (Sinapis alba) and barley (Hordeum sativum), and have been followed also by the measurement of polyphenol-oxidase, peroxidase and dehydrogenase enzyme activity. 

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. 

Further validation of the mechanism proposed for the catecholase activity of the dicopper complexes [Cu2(L66)]" , [Cu2(L55)], and [Cu2(EBA)]" " (Scheme 17) has been obtained investigating the inhibitory effect of kojic acid [5-hydroxy-2-(hydroxymethyl)-y-pyrone] (154). This fungal metabolite is one of the most efficient inhibitors of mushroom tyrosinase and other polyphenol oxidases (160,161). When the catalytic oxidation of DTBCH2 was studied in the presence of kojic acid, strong competitive inhibition was observed in the steps exhibiting substrate concentration dependence,... 

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