BLBS102-c13 BLBS102-Simpson March 21, 2012 13:15 Trim: 276mm X 219mm Printer Name: Yet to Come
13 Seafood Enzymes 257The manufacture of surimi products involves the use of a slow
temperature-setting process, which can be in the temperature
range of 4–40◦C, followed by a heating process involving tem-
peratures of 50–70◦C, which results in the gel strength being
enhanced (Park 2000). Surimi-based products are very impor-
tant fish products in the Asian and Southeast Asian countries,
where Japan has the largest production and marketing of surimi-
based products. The quality and the price are closely dependent
on the gel strength (Park 2000).
The enzyme transglutaminase plays an important role in the
gelation process through catalyzing the cross-linking of the ac-
tomyosin (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 addition of micro-
bial 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 action 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 soft-
ening: cysteine cathepsin and 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 softening of the gel is more pronounced in some
fish species than in others.
A study by An et al. (1994) indicated that the cysteine pro-
teinase cathepsin L contributes to degradation of the myofibrils
in surimi at a temperature of about 55◦C during the heating
process, a result substantiated 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 SEAFOODUtilization 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
research: (1) the cold-adaptation properties of seafood enzymes
and (2) the increasing production of marine by-products used
as potential sources of enzymes. 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.Improved Processing of RoeRoe 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, herring, lumpfish, and cod, has also
gained wide acceptance. 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 linkages 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 of Fish SilageFish 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 manufacture, the fish material is mixed with 1–3.5% formic
acid solution, reducing pH to 3–4. This is optimal for the intesti-
nal proteases and aspartic muscle proteases contained in the
fish material, allowing the solubilization 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 man-
ufactured from cod viscera. They were able to show that fish
by-products having low protease activity could be hydrolyzed
and used for silage by adding protease-rich cod viscera.Deskinning and Descaling of FishDeskinning fish enzymatically can increase the edible yield
as compared with that achieved by mechanical deskinning
(Gildberg et al. 2000). It also provides the possibility of uti-
lizing alternative species such as skate, the skin of which is
very difficult to remove mechanically without ruining the flesh
(Stef ́ansson and Steingrimsdottir 1990). It has been shown that
herring can be deskinned enzymatically by use of acid proteases
obtained from cod viscera (Joakimsson 1984). Enzymatic re-
moval of the skin of other species has been reported as well.
Kim et al. (1993) have described removal of the skin of filefish
by use of collagenase extracted from the intestinal organs of the
fish. Crude protease extract obtained from minced arrowtooth
flounder has been found to be effective in solubilizing the skin
of pollock (Tschersich and Choudhury 1998).
Removing squid skin can be a difficult task. Skinning ma-
chines only remove the outer skin of the squid tubes, leaving the
tough rubbery inner membrane. Strom and Raa (1991) reported
a gentler and more efficient enzymatic method of deskinning
the squid, using digestive enzymes from the squid itself. Also,
a method for deskinning the squid by making use of squid liver
extract has been developed by Leuba et al. (1987).