Food Biochemistry and Food Processing

12

Pectic Enzymes in Tomatoes

M. S. Kalamaki, N. G. Stoforos, and P. S. Taoukis*

271

Introduction

Structure of the Pectin Network in Cell Walls of

Higher Plants

Fractionation of Pectic Substances

Biochemistry of Pectic Enzymes in Tomato

Polygalacturonase

Pectin Methylesterase


-Galactosidase

Pectate Lyase

Genetic Engineering of Pectic Enzymes in Tomato

Genetic Engineering of PG in Tomato Fruit

Genetic Engineering of PG and Food Processing

Genetic Engineering of PME in Tomato Fruit

Genetic Engineering of PME and Food Processing

Genetic Engineering of 
-Galactosidase in Tomato

Fruit

Double Transgenic Tomato Lines in Food Processing

Suppressed PG and Suppressed Exp1

Suppressed PG and Suppressed PME

Tomato Processing

Thermal Inactivation

High-Pressure Inactivation

Future Perspectives

Acknowledgments

References

INTRODUCTION

In this chapter, the enzymes that act on the pectin

fraction of tomato cell walls are presented. In the

introduction, background information on the struc-

ture of the pectin network in cell walls of higher

plants as well as the method used for fractionation

analysis of pectic substances are given. Next, pectic

enzymes in tomato in terms of the genes that code

pectin modifying enzymes, their expression profiles

during fruit ripening, and the activities of the protein

are discussed. Furthermore, attempts to alter the

expression of these enzymes using genetic engineer-

ing in order to retard fruit deterioration at the later

stages of ripening, increase fruit firmness and shelf

life, and improve processing characteristics of toma-

to products are described. Finally, the inactivation

kinetics (by heat and high hydrostatic pressure) of

two pectic enzymes, polygalacturonase (PG) and

pectin methylesterase (PME), are discussed.

STRUCTURE OF THEPECTINNETWORK IN

CELLWALLS OFHIGHERPLANTS

The primary cell wall of higher plants constitutes a
complex network, mainly constructed of polysac-
charides and structural proteins. Two coextensive
structural networks can be identified (Fig. 12.1), the
cellulose-matrix glycan (hemicellulose) network,
consisting of cellulose microfibrils held together by
matrix glycans, and the pectin network (Carpita and
Gibeaut 1993). The cell wall provides shape and
structural integrity to the cell, functions as a protec-
tive barrier to pathogen invasion, and provides signal
molecules important in cell-to-cell signaling, and in
plant-symbiote and plant-pathogen interactions.
Pectin is an elaborate network of highly hydrated
polysaccharides, which fills in the spaces between
the microfibrils in the cellulose-matrix glycan net-
*Corresponding author. work. Pectins can be classified in three major groups:

Food Biochemistry and Food Processing

Edited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing