Oxidation of Chlorogenic Acid, Catechins, and 4-Methylcatechol in Model Solutions by Combinations of Pear (Pyrus communis Cv. Williams) Polyphenol Oxidase and Peroxidase:  A Possible Involvement of Peroxidase in Enzymatic Browning

Abstract

To clarify the role of pear peroxidase (POD) in enzymatic browning, oxidation of 4-methylcatechol, chlorogenic acid, and (−)-epicatechin catalyzed by purified polyphenol oxidase (PPO), purified POD, or combinations of the two enzymes was followed by HPLC. It was shown that pear POD had no oxidative (oxygen dependent) activity. However, in presence of PPO, POD enhanced the phenol degradation. Moreover, when PPO was entirely inhibited by NaCl after different oxidation times, addition of POD led to a further consumption of the phenolic compound. Two mechanisms have been proposed to explain this additional consumption. First, our results have demonstrated that, whatever the substrate used, PPO oxidation generated H2O2, the amount of which varies with the phenolic structure. Second, quinonic forms are used by POD as peroxide substrate. These two mechanisms associated with the kinetic properties of pear PPO and POD are consistent with an effective involvement of pear POD in enzymatic browning. Keywords: Enzymatic browning; pear; peroxidase; polyphenol oxidase

Biochemical Responses of Chestnut Oak to a Galling Cynipid

“…We also found that neither galled nor control chestnut oak tissues contained PPO, although we have measured vigorous PPO activity in tissues from other plant species under the same analytical conditions. Although PPO is present in a number of plants (Richard-Forget and Gauillard, 1997;Shin et al, 1997;Halder et al, 1998) and could reinforce some anti-herbivore functions of POX (Felton et al, 1994;Haruta et al, 2001), it may be absent (Grisebach, 1981) or difficult to extract from some plant tissues (Hsu et al, 1988;Burton and Kirchmann, 1997). We have found previously that PPO activity is low or absent in the leaves of chestnut oak (H. M. Appel and J. C. Schultz, unpublished data), and conclude that this enzyme either is not present in chestnut oak tissue, is present in an inactive form, or is not detectable using the methods employed.…”

Oxidative discolouration in whole-head and cut lettuce: biochemical and environmental influences on a complex phenotype and potential breeding strategies to improve shelf-life

“…In a further complication, some authors have attributed a partial role in the browning response to peroxidases (POD) (Richard-Forget and Gauillard 1997;Degl'Innocenti et al 2005). POD enzymes are part of the lignification process at wound sites and require the presence of hydrogen peroxide (H 2 O 2 ).…”

Alternative pathway implicated as an influencing factor in the synthesis of theaflavin

“…PPO has been partially purified from Blanquilla pear [9] and purified from the pear varieties Ankara Armutu pear [44], d'Anjou pear [41], La France pear [3], Bartlett pear [8] and Williams pear [26]. The aim of the current study was to investigate the use of endogenous enzymes present in the homogenates of various pear varieties as well as endogenous enzymes from Yacon leaves to increase the synthesis of theaflavin starting from green tea.…”