Protein–protein
crosslinking in
food: methods,
consequences,
applications
Juliet A. Gerrard
Department of Plant & Microbial Sciences, University
of Canterbury, Christchurch, New Zealand
(Tel.: +64-3366-7001; fax: +64-3364-2083;
e-mail: j.gerrard@botn.canterbury.ac.nz)
Protein–protein crosslinks play an important role in deter-
mining the functional properties of food proteins. Manip-
ulation of the number and nature of such protein crosslinks
during food processing offers a means by which the food
industry can manipulate the functional properties of food,
often without damaging the nutritional quality. This review
discusses advances in our understanding of protein cross-
linking over the last decade, and examines current and
future applications of this chemistry in food processing.
# 2003 Elsevier Science Ltd. All rights reserved.
Background
Determining the relationship between the structure of
any protein and its function is a challenge that bioche-
mists struggle to meet in many contexts. For the food
technologist, correlating the structure of a food protein
with its function, or functionality, within a food is still
more difficult. Food proteins are often denatured during
processing, so the food technologist must understand
the protein both as a biological entity with a pre-
determined function, and as a randomly coiled biopo-
lymer. To understand and manipulate food proteins
thus requires a knowledge of both protein biochemistry
and polymer science. If the protein undergoes chemical
reaction during processing, both the natural function of
the molecule, and the properties of the denatured poly-
meric state may be influenced. One type of chemical
reaction that has major consequences for protein func-
tion in either their native or denatured states is protein
crosslinking. It is, therefore, no surprize that protein
crosslinking can have profound effects on the functional
properties of food proteins.
Excellent reviews surveying protein crosslinking in
food were published several years ago (Feeny & Whi-
taker, 1988; Matheis & Whitaker, 1987; Singh, 1991).
This review draws on these earlier works, but focuses on
literature published in the last decade. It begins by
defining the different types of protein crosslinks that can
occur in food, before and after processing, and the
consequences of these crosslinks for the functional and
nutritional properties of the foodstuff. Methods that
have been employed to introduce crosslinks into food
deliberately are then reviewed, and future prospects for
the use of this chemistry for the manipulation of food
during processing are surveyed.
The types of crosslinks found in food
Protein crosslinking refers to the formation of covalent
bonds between polypeptide chains within a protein
(intramolecular crosslinks) or between proteins (inter-
molecular crosslinks) (Feeney & Whitaker, 1988). In
biology, crosslinks are vital for maintaining the correct
conformation of certain proteins, and may control the
degree of flexibility of the polypeptide chains. As biolo-
gical tissues age, further protein crosslinks may form that
often have deleterious consequences throughout the
body, and play an important role in the many conditions
of ageing (Zarina et al., 2000). Similar chemistry to that
which occurs during ageing may take place if biological
tissues are removed from their natural environment—for
example, when harvested as food for processing.
Food processing often involves high temperatures,
extremes in pH, particularly alkaline, and exposure to
oxidizing conditions and uncontrolled enzyme chem-
istry. Such conditions can result in the introduction of
protein crosslinks, producing substantial changes in the
structure of proteins, and therefore the functional
(Singh, 1991) and nutritional (Friedman, 1999a, 1999b,
1999c) properties of the final product. A summary of
known protein crosslinking in foods is given in Fig. 1, in
which the information is organised according to the
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PII: S0924-2244(02)00257-1
Trends in Food Science & Technology 13 (2002) 391–399