Polyphenol oxidases and peroxidases are among the most studied enzymes in fruits and vegetables. Owing to the deleterious effects of discoloration and off-flavor formation induced by their actions, these enzymes have not ceased to be a matter of concern to food technologists, while their versatility as catalyst and their diversity as protein present a challenge to the biochemist. This article gives an account on the present state of knowledge in this field. The occurrence of polyphenol oxidases and peroxidases in food and food raw materials, and their role and importance in food processing are briefly outlined. Results of biochemical research including catalytic properties, substrate specificity, susceptibility towards pH and temperature, action of inhibitors, isolation, purification, and characteristics of the enzymes are given, with special emphasis on recent achievements based on high resolution separation and isoenzyme techniques. Finally, the behavior of polyphenol oxidase and peroxidase in selected major groups of fruits and vegetables is discussed. Some contradictions found in the literature are pointed out and some questions that have not been given the necessary attention by researchers so far are mentioned.

Polyphenol oxidase and peroxidase in fruits and vegetables.

Review of the use of biosensors as analytical tools in the food and drink industries

Enzyme stabilization by immobilization

The Effect of Carbon and Nitrogen Sources on the Level of Metabolic Intermediates in Escherichia coli

Model for the amperometric enzyme electrode obtained through digital simulation and applied to the immobilized glucose oxidase system

The effect of fifteen different pesticides including carbamates, chlorinated hydrocarbons and organophosphurus compounds on cholinesterase from housefly, sugar boll weevll, fire ant and German cockroaches is reported. Since the cholinesterase from each source show different inhibition by various inhibitors, an increase in the specificity of enzyme systems for the determination of pesticides is possible.

S.S. Kuan

Papers

Enzymatic methods of analysis

An improved electrode for the assay of urea in blood

Fluorimetric determination of oxidative enzymes. Analytical applications of the monoamine and diamine oxidase systems.

Effect of pesticides on liver cholinesterases from rabbit, pigeon, chicken, sheep and pig.