BLBS102-c21 BLBS102-Simpson March 21, 2012 13:39 Trim: 276mm X 219mm Printer Name: Yet to Come
400 Part 3: Meat, Poultry and Seafoodsif a complete cross-linking reaction between gelatin and genipin
molecules is required (Yao et al. 2004).TransglutaminaseTransglutaminase (TGase; protein-glutamine-glutamyltrans-
ferase, EC 2.3.2.13) catalyzes an acyl-transfer reaction between
theγ-carboxamide group of peptide-bound glutamine residues
(acyl donors) and a variety of primary amines (acyl accep-
tors), including theε-amino group of lysine residues in certain
proteins (Fig. 21.6). It results in polymerization and inter- or
intramolecular cross-linking of protein via formation ofε-(γ-
glutamyl)lysine linkages (Motoki and Seguro 1998, Ashie and
Lanier 2000). In the absence of amine substrates, water may act
as the acyl acceptor, resulting in deamidation ofγ-carboxamide
group of glutamine to form glutamic acid. Formation of covalent
cross-links between proteins is the basis of the ability of TGase to
modify the physical properties of food protein (Ashie and Lanier
2000). TGases are widely distributed in most animal tissues and
body fluids, and are involved in several biological phenomena,
such as blood clotting, wound healing, epidermal keratinization,
and stiffening of the erythrocyte membrane (Aeschlimann and
Paulsson 1994). They are responsible for the regulation of cellu-
lar growth, differentiation, and proliferation. TGases have also
been discovered in plants (Icekson and Apelbaum 1987), fish
(Araki and Seki 1993), and microorganisms (Ando et al. 1989,
Klein et al. 1992).
Microbial transglutaminase (MTGase) are mass-produced
at low cost by fermentation. MTGase catalyzes the cross-
linking of most food proteins through the formation of an
ε-(γ-glutamyl)lysine bond, in the same way as well-known
mammalian enzymes. MTGase is calcium independent and its
molecular weight is smaller than that of other known enzymes
(Motoki and Seguro 1998). The results of many studies suggestFigure 21.6.Cross-linking reaction between glutamine and lysine
residues induced by transglutaminase.that MTGase, as well as other transglutaminases, has many
potential applications in food processing and other areas.
Babin and Dickinson (2001) studied the influence of trans-
glutaminase cross-linking on the rheology of gelatin gels. The
gel strength might be either reduced or enhanced depending on
whether covalent cross-linking occurred predominantly before
or after the development of triple helix junction zones. The ex-
tensive covalent cross-linking occurred during cold-set process,
and afterward in the molten state, thermoreversible character of
gelatin gel was almost completely lost.
Jongjareonrak et al. (2006c) studied the effect of microbial
transglutaminase (MTGase) on the gel properties of gelatin from
bigeye snapper skin and brownstrip red snapper skin. The addi-
tion of MTGase at concentrations up to 0.005% and 0.01% (w/v)
increased the bloom strength of gelatin gel from bigeye snapper
and brownstripe red snapper, respectively. However, the bloom
strength of gelatin gel from both fish species decreased with
further increase in MTGase concentration. Gomez-Guill ́ en et al. ́
(2001) reported that the addition of microbial transglutaminase
to a fish skin gelatin can considerably raise melting point, gel
strength, and viscosity at 60◦C, depending on the concentration
of the enzyme and the incubation time. Increasing concentrations
of TGase increase the elasticity and cohesiveness of the gels, but
result in lower gel strength and hardness because they produce
excessively rapid gel network formation (Gomez-Guill ́ en et al. ́
2001). Recently, Norziah et al. (2009) reported that the addition
of MTGase with the concentration of 0.5 and 1.0 mg/g gelatin
into fish gelatin extracted from the wastes of fish herring species
(Tenualosa ilisha) had higher gel strength than that without the
addition of enzyme, while enzyme concentration above 1.0 mg/g
gelatin resulted in a decreasing gel strength. Adding a high con-
centration of TGase or cross-linking before gelation would be
detrimental to gel strength (Babin and Dickinson 2001). Regen-
stein and Zhou (2007a) also suggested that TGase should not be
added over an appropriate enzyme concentration. The reaction
should occur during or after gel development to obtain the de-
sired cross-linking. Additionally, Fernandez-Diaz et al. (2001)
reported that the gelatin from hake skin had the highest bloom
strength with the addition of 10 mg transglutaminase/g.Use of hydrocolloidsFood products are composed of a wide range of ingredients such
as proteins and carbohydrate-based polysaccharides (Ye 2008).
Complex formation between proteins and polysaccharides
occurs at pH values below the isoelectric point (IEP) of the
proteins and at low ionic strength, usually<0.3 (Ye 2008). Pro-
tein molecules have a net positive charge and behave as poly-
cations at pH values below the IEP (De Kruif et al. 2004).
At mildly acidic and neutral pH values, which are typical
of most foods, carboxyl-containing polysaccharides behave as
polyanions (Ye 2008). Electrostatic complex formation between
proteins and anionic polysaccharides generally occurs in the
pH range between the pKavalue of the anionic groups (car-
boxyl groups) on the polysaccharide and the IEP of the protein
(Tolstoguzov 1997).