Enzymes in fish processing - Enzymes in Food Technology - page 228

Bigeye snapper Brownstripe red

(a) (c)

PSU 6704 10 kV 1 µ m × 10 000 PSU 6708 10 kV 1 µ m × 10 000

(b) (d)

PSU 6709 10 kV 1 µ m × 10 000 PSU 6706 10 kV 1 µ m × 10 000

Fig. 10.8 ). (a) and (b) Gelatin gels of bigeye snapper

skin without and with 0.005% (w/v) MTGase, respectively. (c) and (d) Gelatin gels of brownstripe red
snapper skin without and with 0.01% (w/v) MTGase, respectively. 120 (Reprinted from Ref. [49], Copyright
(2007), with permission from Elsevier.)

Microstructure of gelatin (magnification: 10 000 ×

10.3.2.2 Use of MTGase in gelatin gels and films

Fish gelatin has become increasingly interesting as an alternative for gelatin from land animal
sources such as bovine and porcine skin and bone. This is associated with the outbreak of
bovine spongiform encephalopathy (BSE) and the foot and mouth disease (FMD) crisis,
as well as with aesthetic and religious objections. 120 Gelatin can be extracted from various
marine sources. However, collagen and gelatin from fish, especially from cold water fish,
have low gelling temperatures and melting points. 121 This limits the use of fish gelatin since
it cannot form a gel at room temperature. 122 Also, the bloom strength is generally lower
than its mammalian counterpart. Therefore, MTGase have been used to improve the bloom
strength of gelatin gel from fish origin via cross-linking of gelatin molecules in the gel matrix.
To maximize the bloom strength of gelatin, the appropriate amount of MTGase should be
considered. If the enzyme concentration is too low, gel formation cannot occur. The addition
of MTGase at levels up to 0.005% and 0.01% increased the bloom strength of gelatin gel
from bigeye snapper and brownstripe red snapper skin, respectively. Nevertheless, the bloom
strength of skin gelatin gel from both fish species decreased with further increase in MTGase
levels. With addition of MTGase, denser aggregates with negligible voids in gel network
were noticeable, most likely due to the formation of non-disulphide covalent bonds between
adjacent molecules (see Fig. 10.8).
Cross-linking induced by MTGase is also governed by gelatin concentration. Sufficient
gelatin concentration renders the better gel than do lower concentrations. 123 MTGase could
induce cross-linking of fish gelatin at 4-5 ◦ C. MTGase cross-linked gelatin from Baltic cod
did not melt in boiling water after 30 min of heating. 123 MTGase showed a higher gel
enhancing effect than MgSO 4 for gelatin from hake and cod skin. 124 Optimal level for gel