Food Biochemistry and Food Processing

9

Protein Cross-linking in Food

J. A. Gerrard

223

Introduction
Protein Cross-links in Food
Disulfide Cross-links
Cross-links Derived from Dehydroprotein
Cross-links Derived from Tyrosine
Cross-links Derived from the Maillard Reaction
AGE Protein Cross-links Isolated to Date in Food
Melanoidins
Maillard-Related Cross-links
Cross-links Formed via Transglutaminase Catalysis
Other Isopeptide Bonds
Manipulating Protein Cross-linking during Food Processing
Chemical Methods
Enzymatic Methods
Transglutaminase
Future Applications of Protein Cross-linking
Acknowledgments
References

INTRODUCTION

Protein cross-links play an important role in deter-
mining the functional properties of food proteins.
Manipulation of the number and nature of protein
cross-links during food processing offers a means
by which the food industry can manipulate the
functional properties of food, often without damag-
ing the nutritional quality. This chapter discusses ad-
vances in our understanding of protein cross-linking
over the last decade and examines current and future
applications of this chemistry in food processing. It
builds on, and updates, two recent reviews in this

area (Gerrard 2002, Miller and Gerrard 2004) in

addition to earlier reviews on this subject (Matheis

and Whitaker 1987, Feeney and Whitaker 1988,

Singh 1991).

The elusive relationship between the structure and

the function of proteins presents a particular chal-

lenge for the food technologist. Food proteins are

often denatured during processing, so there is a need

to understand the protein both as a biological entity

with a predetermined function and as a randomly

coiled biopolymer. To understand and manipulate

food proteins thus requires a knowledge of both pro-

tein biochemistry and polymer science. If the pro-

tein undergoes chemical reaction during processing,

both the “natural” function of the molecule, and the

properties of the denatured polymeric state may be

influenced. One type of chemical reaction that has

major consequences for protein function in either

their native or denatured states is protein cross-

linking. It is, therefore, no surprise that protein

cross-linking can have profound effects on the func-

tional properties of food proteins.

This chapter sets out to define the different types

of protein cross-links that can occur in food, before

and after processing, and the consequences of these

cross-links for the functional and nutritional proper-

ties of the foodstuff. Methods that have been em-

ployed to introduce cross-links into food deliberate-

ly are then reviewed, and future prospects for the use

of this chemistry for the manipulation of food dur-

ing processing are surveyed.

Food Biochemistry and Food Processing

Edited by Y. H. Hui

Copyright © 2006 by Blackwell Publishing