A A C C   2 0 0 0   A n n u a l   M e e t i n g

Polyphenol oxidase (EC 1.14.18.1) is a copper containing enzyme that is widely distributed in plants and other organisms. This enzyme catalyzes two reactions in the presence of molecular oxygen: Hydroxylation of monophenols to o-diphenols (monophenolase activity) and oxidation of o-diphenols to o-quinones (diphenolase activity) which then non-enzymatically polymerize into red, brown or black pigment (melanin). It is this latter property of polyphenol oxidase (PPO) that makes it an important enzyme in food industry. It has been shown to cause browning in some of the wheat-based food products. This enzyme can be found in either latent or active form in a number of studied sources. The activatable latent form seems to predominate as shown to be the case in the present study. However, the mechanism of its activation is not fully understood. We have therefore studied the activation and inhibition of PPO in a variety of cultivars employing various chemicals. The results show that latent PPO can be activated and the activated form can be inhibited by a range of compounds of diverse chemical nature. Attempts have been made to categorize these compounds and assess the relationships between their structure and molecular mode of interaction with PPO.