Polyphenols pears

Aires V, Adote S, Hichami A, Moutairou K, Boustani ES, Khan NA. 2004. Modulation of intracellular calcium concentrations and T cell activation by prickly pear polyphenols. Mol Cell Biochem 260 103-110. 

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 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... 

Catechins Epigallocatechin, epicatechin gallate. and epicatechin. They are the main polyphenols in green tea. Other sources are apples, cherries, and pears. Down regulation of mutagenic signalling [841. 10-300... 

Richard-Forget, F.C. and GauUlard, F.A. Oxidation of chlorogenic acid, catechins, and 4-methylcatechol in model solutions hy combinations of pear Pyrus communis Cv. Williams) polyphenol oxidase and peroxidase A possible involvement of peroxidase in enzymatic browning, J. Agric. Food Chem., 45, 2472, 1997. 

Halim, D.H. and Montgomery, M.W. Polyphenol oxidase of d Anjou pears (pyrus communis L.), J. Food... 

The o-quinones formed from phenolics further enhance the intensity of browning by oxidation of other substrates, complexing with amino acids and protein, and polymerization. Non-enzymatic discoloration is believed to involve metal-polyphenol complexing as reported in the processed potato (Bate-Smith et al., 1958), cauliflower (Donath, 1962), and asparagus (DeEds and Couch, 1948), conversion of leucoanthocyanidins to pink anthocyanidins in the processed broad bean (Dikinson et al., 1957), green bean puree (Roseman et al., 1957), and canned Bartlett pear (Luh et al., 1960), and protein-polyphenol complexing in chilled or stored beer (Schuster and Raab, 1961). 

Sioud FB, Luh BS (1966) Polyphenolic compounds in pear puree. Food Technol 20 535-538... 

Examples of simple phenols (Ce) include catechol and phloroglucinol. Although most of the more complex plant polyphenols contain these two simple phenols as a parts of their stracmres, catechol and phloroglucinol are uncommon in plant tissues. Catechol has been found in leaves of Gaultheria species, while phloroglucinol has been found as glucoside in the peel of various Citrus fruits. Arbutin (III) is found in leaves of various Vaccinium spp., such as bluebeny, cranberry, cowberry, and pear trees (Pyrus communis L., Rosaceae) [41-43]. 

M. Smith and M. W. Montgomery, Improved methods for the extraction of polyphenol oxidase from d Anjou pears. Phytochemistry 24 901 (1985). 

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