Food Biochemistry and Food Processing

392 Part III: Muscle Foods

The enzyme transglutaminase plays an important
role in the gelation process through catalyzing the
cross-linking of the actomyosin (An et al. 1996).
Some of the differences in gelling capability among
different species are due to the properties and levels
of activity of muscle transglutaminase (An et al.
1996, Lanier 2000). Studies have shown that the ad-
dition of microbial transglutaminase can increase
the gel strength obtained in fish species having low
transglutaminase activity (Perez-Mateos et al. 2002,
Sakamoto et al. 1995). The effect of transglutami-
nase on the processing of surimi has been reviewed
extensively by An et al. (1996) and by Ashie and
Lanier (2000).
A softening of the gel during the temperature-
setting and heating processes can occur due to auto-
lysis of the myosin and actomyosin through the ac-
tion of endogenous heat-stable proteinases. Whether
or not this occurs is partly a function of the species
used for the surimi production. Two groups of pro-
teinases have been identified as being responsible
for the softening: cysteine cathepsin and heat-stable
alkaline proteinases (HAP).
The presence of HAP in the muscle of different
fish species used for surimi production and the
effects it has on degradation of the fish gel during
the heating process have been taken up in a number
of studies (Makinodan et al. 1985, Toyahara et al.
1990, Cao et al. 1999). The finding of Kinoshita et
al. (1990b) that the fish species differ in the amount
of HAP in muscle, could partly explain why soften-
ing of the gel is more pronounced in some fish
species than in others.
A study by An et al. (1994) indicated that the cys-
teine proteinase cathepsin L contributes to degrada-
tion of the myofibrils in surimi at a temperature of
about 55°C during the heating process, a result sub-
stantiated by Ho et al. (2000), who also measured
the softening of mackerel surimi upon the addition
of mackerel cathepsin L.

TECHNOLOGICAL
APPLICATIONS OF ENZYMES
FROM SEAFOOD

Utilization of enzymes from seafood as technical
aids in both seafood processing and other areas of
food and feed processing has been an area of active
research for many years. There are two factors that
have provided the primary motivation for such re-
search: (1) the cold-adaptation properties of seafood

enzymes and (2) the increasing production of ma-

rine by-products used as potential sources of en-

zymes. Although the results have been promising,

many of the potential technologies are still in their

initial stages of development and are not yet fully

established industrially.

IMPROVEDPROCESSING OFROE

Roe is considered by many to be a seafood delicacy.

Russian caviar, produced from the roe of sturgeon, is

the form best known, although roe produced from a

variety of other species, such as salmon, trout, her-

ring, lumpfish, and cod, has also gained wide accep-

tance. The roe is originally covered by a two-layer

membrane (chorion) termed the roe sack. In some

species, mechanical or manual separation of the roe

from the sack results in damage to the eggs and in

yields as low as 50% (Gildberg 1993). Pepsin-like

proteases isolated from the intestines of seafood

species, as well as collagenases from the hepatopan-

creas of crabs, have been shown to cleave the link-

ages between the sac and the eggs without damaging

the eggs. Such enzyme treatment has been reported

to increase the yield from 70% to 90% (Gildberg et

al. 2000, and references therein).

PRODUCTION OFFISHSILAGE

Fish silage is a liquid nitrogenous product made

from small pelagic fish or fish by-products mixed

with acid. It is used as a source of protein in animal

feed (Aranson 1994, Gildberg 1993). In its manufac-

ture, the fish material is mixed with 1–3.5% formic

acid solution, reducing pH to 3–4. This is optimal for

the intestinal proteases and aspartic muscle proteas-

es contained in the fish material, allowing the solubi-

lization of the fish material to proceed as an autolytic

process driven by both types of protease (Gildberg et

al. 2000). Gildberg and Almas (1986) have reported

the existence of two very active pepsins (I and II) in

silage manufactured from cod viscera. They were

able to show that fish by-products having low pro-

tease activity could be hydrolyzed and used for

silage by adding protease-rich cod viscera.

DESKINNING ANDDESCALING OFFISH

Deskinning fish enzymatically can increase the edi-

ble yield as compared with that achieved by me-

chanical deskinning (Gildberg et al. 2000). It also