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.

Assay of catechol oxidase—a critical comparison of methods

The phenomena of development and metamorphosis have fascinated biologists and naturalists alike for centuries, and comparative physiologists, biochemists, and endocrinologists have systematically studed these processes for almost a century now. Accordingly, a large body of information has accumulated on various aspects of vertebrate biology relating to growth and transformation. Space limitations require that we restrict our coverage in this chapter primarily to recent work on the endocrine control of development and metamorphosis in amphibians. Hence, we will not be able to consider environmental factors that affect these processes, or the recent findings on the control of transformations in other vertebrates, such as smoltification in salmonids. In addition, we will not be able to cite many pertinent references on the control of growth and metamorphosis even in the amphibians. Readers are referred to the excellent and comprehensive reviews of Frieden and Just (1970) and Dodd and Dodd (1976), and to other chapters in this volume for references on some of the earlier literature not cited by us.

Hormonal Control of Amphibian Metamorphosis

The subject is reviewed under the headings: Polyphenols involved in browning reactions - catechin, leucoanthocyanidins, anthocyanins, flavonols, cinnamic acid derivatives, simple phenols; Enzymic browning reactions in food - polyphenoloxidase enzyme, general considerations regarding isolation and assay of polyphenoloxidases, cresolase activity, catecholase activity, role of copper, substrate specificity of polyphenoloxidases, secondary reactions of o-quinones, inactivation of polyphenoloxidase, activation of polyphenoloxidase, polyphenols and enzymic browning of individual food materials; Nonenzymic discoloration involving polyphenols - food browning caused by metal-polyphenol complexing, involvement of leucoanthocyanins in discoloration, turbidity in beer; Additional research needs.

Food Browning as a Polyphenol Reaction

Digestion and the digestive system

A Spectrophotometric Method for the Determination of the Catecholase Activity of Tyrosinase and Some of its Applications1

The thyroxine-like activity of compounds structurally related to thyroxine.

Cuprous Ion Formation in Cupric Ion Catalyzed Oxidations1,2

Studies on amylase synthesis by pigeon pancreas slices

Methods for Labeling Thyroxine With Radioactive Iodine

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