17 Seafood Enzymes 391muscle protein, contributing to the characteristic
softening of the fillet and liberating free amino acids
and small peptides that help create the characteristic
flavor of the product (Nielsen 1995, Olsen and Skåra
1997). Studies have shown that intestinal trypsin-
and chymotrypsin-like enzymes migrate into the
fillet, where they play an active role in the degrada-
tion of muscle proteins during storage (Engvang and
Nielsen 2000, Stefánsson et al. 2000). Furthermore,
Nielsen (1995) shows that muscle amino peptidases
are also active in the salted herring during storage.
In southern Europe, a similar product based on the
use of whole sardines or anchovies is produced. In
contrast to the salted herring from Scandinavia, these
salted sardines and anchovies are stored at ambient
temperature, which can vary between 18°C and 30°C
(Nunes et al. 1997). Nunes et al. (1997) found that
proteases from both the intestines and the muscles
participated in the ripening of sardines(Sardina pil-
chardus).Hernadez-Herrero et al. (1999) reported an
increase in proteinase activity as well as in protein
hydrolysis during the storage of salted anchovies
(Engraulis encrasicholus)and found a close rela-
tionship between proteolysis and the development of
the sensory characteristics of the product.
PRODUCTION OFFISHSAUCE ANDFISHPASTE
Fish sauce and fish paste are fermented fish products
produced mainly in Southeast Asia, where they are
highly appreciated food flavorings. Fish sauce is the
liquefied protein fraction, and fish paste is the “sol-
id” protein fraction obtained from the prolonged
hydrolysis of heavily salted small pelagic fish. Pro-
duction takes place in closed tanks at ambient tropi-
cal temperatures during a period of several months
(Gildberg 2001, Saishiti 1994). The hydrolysis rep-
resents the combined action of the fishes’ own diges-
tive proteases and of enzymes from halotolerant lac-
tic acid bacteria (Saishiti 1994). Orejani and Liston
(1981) concluded, on the basis of inhibitor studies,
that a trypsin-like protease is one of the enzymes
responsible for the hydrolysis. Vo et al. (1984) de-
tected a high and stable level of activity of intestinal
amino peptidase during the production of fish sauce.
Del Rosario and Maldo (1984) measured the activity
of four different proteases in fish sauce produced
from horse mackerel. During a four-month period
of measurement, they found the activity of cathep-
sins A, C, and B to be stable and that of cathepsin
D to decrease. Raksakulthai and Haard (1992) found
that cathepsin C obtained from capelin was active
in the presence of 20–25% salt, suggesting that
this enzyme is involved in the hydrolysis of capelin
fish sauce. These studies indicate that several dif-
ferent proteases need to be active and that their
concerted action is necessary to achieve the pro-
nounced hydrolysis required for production of such
fish sauces.
It is notable that the similarly high storage tem-
peratures present in southern Europe do not lead to
a solubilization of salted sardines and anchovies.
Ishida et al. (1994) reported that at 35°C salted Jap-
anese anchovies (E. japonica)degraded to a marked
degree, whereas at this temperature salted anchovies
from southern Europe (E. encrasicholus)were struc-
turally stable. Also, they detected a thermostable
trypsin-like proteinase in the muscle of both salted
Japanese anchovies and European anchovies, but its
activity was much higher in the Japanese anchovies.
An explanation of the difference between the Eur-
opean and the Asian products might be a large dif-
ference between the hydrolytic enzyme activity of
the respective raw materials.PRODUCTION OFSURIMISurimi is basically a myofibrillar protein concen-
trate that forms a gel due to cross-linking of its acto-
myosin molecules (An et al. 1996). It is made from
minced fish flesh obtained mainly from pelagic
white fish of low fat content, such as Alaskan pol-
lack and Pacific whiting. The mince is washed sev-
eral times with water to remove undesired elements
such as connective tissue and lipids. The particulate
is then stabilized by cryoprotectants before being
frozen (Park and Morrisey 2000).
Surimi is used as a raw material for the manufac-
ture of various products, such as imitation crabmeat
and shellfish substitutes. The 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 in-
volving temperatures of 50–70°C, which results in
the gel strength being enhanced (Park 2000). Surimi-
based products are very important 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).