Food Biochemistry and Food Processing

4

Browning Reactions

M. Villamiel, M. D. del Castillo, and N. Corzo

71

Introduction
Enzymatic Browning
Properties of Polyphenol Oxidase (PPO)
Substrates
Control of Browning
Nonenzymatic Browning
The Maillard Reaction
Factors Affecting the Maillard Reaction
Study of the Maillard Reaction in Foods
Control of the Maillard Reaction in Foods
Caramelization
Ascorbic Acid Browning
Pathway of Ascorbic Acid Browning
Control of Ascorbic Acid Browning
Lipid Browning
Protein-Oxidized Fatty Acid Reactions
Nonenzymatic Browning of Aminophospholipids
References

INTRODUCTION

Browning reactions are some of the most important
phenomena occurring in food during processing and
storage. They represent an interesting research for
the implications in food stability and technology as
well as in nutrition and health. The major groups of
reactions leading to browning are enzymatic phenol
oxidation and so-called nonenzymatic browning
(Manzocco et al. 2001).

ENZYMATIC BROWNING

Enzymatic browning is one of the most important col-
or reactions that affect fruits, vegetables, and seafood.
It is catalyzed by the enzyme polyphenol oxidase (1,2

benzenediol; oxygen oxidoreductase, EC 1.10.3.1),

which is also referred to as phenoloxidase, phenolase,

monophenol oxidase, diphenol oxidase, and tyrosi-

nase. Phenoloxidase enzymes catalyze the oxidation

of phenolic constituents to quinones, which finally

polymerize to colored melanoidins (Marshall et al.

2000).

Enzymatic browning reactions may affect fruits,

vegetables, and seafood in either positive or negative

ways. These reactions, for instance, may contribute

to the overall acceptability of foods such as tea, cof-

fee, cocoa, and dried fruits (raisins, prunes, dates, and

figs). Products of enzymatic browning play key phys-

iological roles. Melanoidins, produced as a conse-

quence of polyphenol oxidase activity, may exhibit

antibacterial, antifungal, anticancer, and antioxidant

properties. Polyphenol oxidases impart remarkable

physiological functions for developing of aquatic

organisms, such as wound healing and hardening of

the shell (sclerotization) after molting in insects and

in crustaceans such as shrimp and lobster. The

mechanism of wound healing in aquatic organisms

is similar to that which occurs in plants in that the

compounds produced as a result of the polymeriza-

tion of quinones, melanins or melanoidins, exhibit

both antibacterial and antifungal activities. In addi-

tion, enzymatic reactions are considered desirable

during fermentation (Fennema 1976). Despite these

positive effects, enzymatic browning is considered

one of the most devastating reactions for many exot-

ic fruits and vegetables, in particular tropical and

subtropical varieties. Enzymatic browning is espe-

cially undesirable during processing of fruit slices

Food Biochemistry and Food Processing

Edited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing