Food Biochemistry and Food Processing (2 edition)

BLBS102-c12 BLBS102-Simpson March 21, 2012 13:11 Trim: 276mm X 219mm Printer Name: Yet to Come

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Pectic Enzymes in Tomatoes

Mary S. Kalamaki, Nikolaos G. Stoforos, and Petros S. Taoukis

Introduction

Structure of Pectin Network in Cell Walls of Higher

Plants

Fractionation of Pectic Substances

Biochemistry of Pectic Enzymes in Ripening Tomato Fruit

Polygalacturonase

Pectin Methylesterase

β-Galactosidase

Pectate Lyase

Genetic Engineering of Pectic Enzymes in Tomato

Single Transgenic Tomato Lines

Polygalacturonase

Pectin Methylesterase

β-Galactosidase

Double Transgenic Tomato Lines

PG and Expansin

PG and PME

Tomato Processing

Thermal Inactivation

High Pressure Inactivation

Future Perspectives

Acknowledgments

References

Abstract:In this chapter, the enzymes that act on the pectic frac-

tion of the tomato cell wall are described. In a brief introduction,

the structure of the pectin network in cell walls of higher plants and

a methodology for fractionation of pectic substances are presented.

Following, the four most significant pectic enzymes, polygalactur-

onase, pectin methylesterase,β-galactosidase, and pectate lyase are

described in terms of the genes that encode them in tomato, their

expression profiles during fruit ripening, as well as the structure

and activities of the corresponding proteins. Cases of genetic mod-

ification of these enzymes aiming in increasing cell wall integrity,

postharvest shelf life, and the processing characteristics of tomatoes

are also presented. Finally, the inactivation kinetics of tomato pectic

enzymes by heat and high hydrostatic pressure are discussed.

INTRODUCTION

Pectin is a structurally and functionally diverse group of

polysaccharides in the plant cell wall. Apart from its role in

cell wall architecture, it functions in signaling, cell-to-cell

adhesion, determining wall porosity, pH and ionic content, cell

growth and differentiation, plant protection, and it is a major

contributor to fruit texture. Pectin disassembly during ripening

is associated with the development of soft fruit texture, which

in turn determines the textural and rheological characteristics

of the processed fruit products. In addition, pectin is used in

the food industry as a gelling and stabilizing agent in order to

improve food rheological behavior. Among the most studied

pectic polysaccharides are those of tomato fruit. In this chapter,

the enzymes that act on the pectin fraction of tomato cell walls

are presented. In the introduction, background information on

the structure of pectin in cell walls of higher plants as well as a

method used for biochemical analysis of pectic substances are

given. Next, pectic enzymes in tomato in terms of genes that

encode pectin modifying enzymes, their expression profiles

during fruit ripening, and the activities of the respective proteins

are discussed. Furthermore, attempts to alter the expression of

these enzymes using genetic engineering in order to retard fruit

deterioration at the later stages of ripening, increase fruit firm-

ness and shelf life, and improve processing characteristics of

tomato products are described. Finally, the inactivation kinetics

(by heat and high hydrostatic pressure) of two pectic enzymes,

polygalactronase and pectin methylesterase, are discussed.

Structure of Pectin Network in Cell Walls

of Higher Plants

The primary cell wall of higher plants constitutes a complex net-

work, mainly constructed of polysaccharides, structural proteins,

and some phenolics. Two co-extensive structural networks can

Food Biochemistry and Food Processing, Second Edition. Edited by Benjamin K. Simpson, Leo M.L. Nollet, Fidel Toldr ́a, Soottawat Benjakul, Gopinadhan Paliyath and Y.H. Hui.

©C2012 John Wiley & Sons, Inc. Published 2012 by John Wiley & Sons, Inc.

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