BLBS102-c10 BLBS102-Simpson March 21, 2012 13:7 Trim: 276mm X 219mm Printer Name: Yet to Come
216 Part 2: Biotechnology and Enzymologywith other appropriate residues to reform native linkages (Singh
1991).
PDI has been found in most vertebrate tissues and in peas,
cabbage, yeast, wheat and meat (Singh 1991). It has been shown
to catalyse the formation of disulfide bonds in gluten proteins
synthesised in vitro. Early reports suggested that a high level of
activity corresponded to a low bread-making quality (Grynberg
et al. 1977). The use of oxidoreduction enzymes, such as PDI,
to improve product quality is an area of interest to the baking
industry (Watanabe et al. 1998, van Oort 2000, Joye et al. 2009a,
2009b) and the food industry in general (Hjort 2000). The po-
tential of enzymes such as PDI to catalyse their interchange has
been extensively reviewed by Shewry and Tatham (1997).
Sulfhydryl (or thiol) oxidase catalyses the oxidative forma-
tion of disulfide bonds from sulfhydryl groups and oxygen
and occurs in milk (Matheis and Whitaker 1987, Singh 1991).
Immobilised sulfhydryl oxidase has been used to eliminate
the ‘cooked’ flavour of ultra-high temperature-treated milk
(Swaisgood 1980). It is not a well-studied enzyme, although the
enzyme from chicken egg white has received recent attention in
biology (Hoober 1999). Protein disulfide reductase catalyses a
further sulfhydryl–disulfide interchange reaction and has been
found in liver, pea and yeast (Singh 1991).
Peroxidase, lipoxygenase and catechol oxidase occur in vari-
ous plant foods and are implicated in the deterioration of foods
during processing and storage. They have been shown to cross-
link several food proteins, including bovine serum albumin, ca-
sein,β-lactoglobulin and soy, although the uncontrolled nature
of these reactions casts doubt on their potential for food im-
provement (Singh 1991). Lipoxygenase, in soy flour, is used
in the baking industry to improve dough properties and baking
performance. It acts on unsaturated fatty acids, yielding peroxy
free radicals and starting a chain reaction. The cross-linking ac-
tion of lipoxygenase has been attributed to both the free radical
oxidation of free thiol groups to form disulfide bonds and to the
generation of reactive cross-linking molecules such as malondi-
aldehyde (Matheis and Whitaker 1987).
Altering the functional properties of milk proteins by
cross-linking with transglutaminase (see below), as well as the
enzymes lactoglutaminase, lactoperoxidase, laccase and glu-
cose oxidase has recently been studied by Hiller and Lorenzen
(2009). In this study, a qualitative and quantitative overview
of the enzymatic oligomerisation of milk proteins by various
enzymes in relation to transglutaminase was presented, to fill a
gap in understanding of enzymatic oligomerisation of proteins.
A variety of milk proteins were chosen for this study, such as
sodium caseinate, whey protein isolate and skim milk powder.
Interestingly, the results from this study suggest it may be possi-
ble to specifically select the appropriate modified protein to use
for specific industrial applications, depending upon the require-
ments of the food proteins and the desired functional protein
properties.
All enzymes discussed so far have been over-shadowed in
recent years by the explosion in research on the enzyme trans-
glutaminase. Due largely to its ability to induce the gelation
of protein solutions, transglutaminase has been investigated for
uses in a diverse range of foods and food-related products. Theuse of this enzyme has been the subject of a series of recent re-
views, covering both the scientific and patent literature (Nielson
1995, Zhu et al. 1995, Motoki and Seguro 1998, Kuraishi et al.
2001, Yokoyama et al. 2004, Jaros et al. 2006,Ozrenk 2006). ̈
These are briefly highlighted below.TransglutaminaseThe potential of transglutaminase in food processing was hailed
for many years before a practical source of the enzyme became
widely available. The production of a microbially derived en-
zyme by Ajinomoto Inc. proved pivotal in paving the way for
industrial applications (Motoki and Seguro 1998). In addition,
the transglutaminases that were discovered in the early years
were calcium-ion dependent, which imposed a barrier for their
use in foods that did not contain a sufficient level of calcium.
The commercial preparation is not calcium dependent and thus
finds much wider applicability (Motoki and Seguro 1998). The
production of microbial transglutaminase, derived fromStrep-
toverticillium mobaraense,is described by Zhu et al. (1995) and
methods with which to purify and assay the enzyme are reviewed
by Wilhelm et al. (1996). The commercial enzyme operates ef-
fectively over the pH range 4–9, from 0◦Cto50◦C (Motoki and
Seguro 1998).
There is a seemingly endless list of foods in which the use
of transglutaminase has been successfully used (De Jong and
Koppelman 2002): seafood, surimi, meat, dairy (Hiller and
Lorenzen 2009), baked goods, sausages (as a potential replace-
ment for phosphates and other salts), gelatin (Kuraishi et al.
2001), spaghetti (Aalami and Leelavathi 2008), noodles and
pasta (Larre et al. 1998, 2000). It is finding increasing use in
restructured products, such as those derived from scallops and
pork (Kuraishi et al. 1997). In all cases, transglutaminase is
reported to improve firmness, elasticity, water-holding capacity
and heat stability (Kuraishi et al. 2001). It also has potential to al-
leviate the allergenicity of some proteins (Watanabe et al. 1994).
Dickinson (1997) reviewed the application of transglutaminase
to cross-link different kinds of colloidal structures in food and
enhance their solid-like character in gelled and emulsified sys-
tems, controlling rheology and stability. These applications are
particularly appealing in view of the fact that cross-linking
by transglutaminase is thought to protect nutritionally valu-
able lysine residues in food from various deteriorative reactions
(Seguro et al. 1996). Furthermore, the use of transglutaminase
potentially allows production of food proteins of higher nutri-
tional quality, through cross-linking of different proteins con-
taining complementary amino acids (Zhu et al. 1995).
The use of transglutaminase in the dairy industry has been
explored extensively. The enzyme has been trialled in many
cheeses, from Gouda to Quark, and the use of transglutaminase
in ice cream is reported to yield a product that is less icy and
more easily scooped (Kuraishi et al. 2001). Milk proteins form
emulsion gels that are stabilised by cross-linking, opening new
opportunities for protein-based spreads, desserts and dressings
(Dickinson and Yamamoto 1996). The use of transglutaminase
has been explored in an effort to improve the functionality of
whey proteins (Truong et al. 2004, Gauche et al. 2008, 2010), for