Characterization of Catecholase and Cresolase Activities of Eggplant Polyphenol Oxidase

Abstract

In the present paper the catecholase and cresolase activities of eggplant polyphenol oxidase (PPO) are described. To preserve the latter activity, a partially purified enzyme was used. Peroxidase was removed from the preparation to avoid its interference with PPO during phenol oxidation. The partially purified eggplant PPO was fully active. The catecholase/cresolase ratio of 41.1 indicated that, in a pH close to the physiological, diphenol oxidation predominates over monophenol oxidation. The characteristic lag phase of the cresolase activity is modulated by the pH, the monophenol and diphenol concentrations, and the enzyme's concentration. The effect of several inhibitors was also tested, and the K(i) values of the two most effective (tropolone and 4-hexylresorcinol) were determined.

Polyphenoloxidase from Riesling and Dornfelder wine grapes (Vitis vinifera) is a tyrosinase

“…Our results support the very recent observation of tyrosinase activity of another plant PPO from the walnut (Juglans regia) which has an active N-terminal domain with a similar size (Asp101-Arg445) (Zekiri et al, 2014). In addition, several years ago tyrosinase activity was reported in few plant-PPOs (Gowda & Paul, 2002;OrenesPinero, García-Carmona & Sanchez-Ferrer, 2005;Pérez-Gilabert & García-Carmona, 2000). Grape PPO has a higher affinity toward the monophenolic substrate tyramine compared to the diphenol dopamine, but lower turnover rates.…”

Effect of 24-epibrassinolide treatment on the metabolism of eggplant fruits in relation to development of pulp browning under chilling stress

“…Pulp and seed browning is the most common chilling injury symptom of eggplant fruit (Pérez-Gilabert and García-Carmona 2000). The same phenomenon was detected by visual inspection in this study (Fig.…”

“…Low temperature storage is an effective method to prolong the postharvest life, however, eggplant fruits are chilling sensitive and can develop some chilling injury symptoms when stored below 7-10°C (Fallik et al 1995). Pulp and seed browning is the most common chilling injury symptom in eggplant fruits accompanied by the development of off-flavour (Pérez-Gilabert and García-Carmona 2000;Concellón et al 2004). In China, eggplant fruits harvested in winter and early spring show higher levels of pulp browning compared to those harvested in other months of the year, which severely restricts the economic importance of the eggplant on account of its negative impact on palatability and consumer acceptability in terms of appearance, freshness and taste.…”

First evidence of laccase activity in the Pacific oyster Crassostrea gigas

“…2) and ammonium tetramolybdate (data not shown), an effect was observed on the autoxidation of, at least, one laccase substrate. SHAM and kojic acid are PO inhibitors but not laccase specific [37,46]. Therefore, although CTAB is also known as a cationic detergent, it appeared to be the most pertinent laccase inhibitor.…”