Food Biochemistry and Food Processing

17 Seafood Enzymes 393

provides the possibility of utilizing alternative
species such as skate, the skin of which is very diffi-
cult to remove mechanically without ruining the
flesh (Stefánsson and Steingrimsdottir 1990). It has
been shown that herring can be deskinned enzymat-
ically by use of acid proteases obtained from cod
viscera (Joakimsson 1984). Enzymatic removal 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 pol-
lock (Tschersich and Choudhury 1998).
Removing squid skin can be a difficult task. Skin-
ning machines only remove the outer skin of the
squid tubes, leaving the tough rubbery inner mem-
brane. 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).
For certain markets, such as Japanese sashimi
restaurants and fresh fish markets, skin-on fillets
without the scales are demanded. Also, fish skin is
used in the leather industry, where descaling is like-
wise necessary. Obtaining a prime quality product
requires gentle descaling. Mechanical descaling can
be difficult to accomplish without the fish flesh be-
ing damaged, especially in the case of certain soft-
fleshed species, where enzymatic descaling results
in a gentle descaling (Svenning et al. 1993). Di-
gestive enzymes of fish have proved to be useful for
removing scales gently (Gildberg et al. 2000).

IMPROVEDPRODUCTION OFFISHSAUCE

As already indicated, the original process for manu-
facturing fish sauce is carried out at high ambient
temperature, involving the use of an autolytic pro-
cess catalyzed by endogenous proteases. The rate of
the hydrolysis depends on the content of digestive
enzymes in the fish. There has been an obvious
interest, however, in shortening the time required for
producing the fish sauce, and use has also been
made of other fish species, such as Arctic capelin
and Pacific whiting. Arctic capelin is usually caught
during the winter, when the fish has a low feed
intake and its digestive enzyme content thus is low.
Research has shown, however, that supplementing

Arctic capelin with cod intestines or squid pancreas,

both of which are rich in digestive enzymes, allows

an acceptable fish sauce to be produced during the

winter (Gildberg 2001, Raksakulthai et al. 1986).

Tungkawachara et al. (2003) showed that fish sauce

produced from a mixture of Pacific whiting and suri-

mi by-products (head, bone, guts, and skin from

Pacific whiting) has the same sensory quality as a

commercial anchovy fish sauce.

SEAFOODENZYMESUSED INBIOTECHNOLOGY

The poor temperature stability of seafood enzymes

is a useful property that has lead to the production

of enzymes useful in gene technology, where only

very small amounts of enzymes are needed. Alka-

line phosphatase from cold-water shrimp (Pandalus

borealis)is more heat labile than alkaline phos-

phatases from mammals and can be denaturated at

65°C for 15 minutes (Olsen et al. 1991). The heat-

labile enzyme is therefore more suitable as a DNA-

modifying enzyme in gene-cloning technology,

where higher temperatures can denaturate the DNA.

The enzyme is recovered for commercial use from

shrimp-processing wastewater in Norway. Other sea-

food enzymes with heat-labile properties, such as

Uracil-DNA N-glycosylase from cod (Lanes et al.

2000), and shrimp nuclease, are likewise produced

commercially as recombinant enzymes for gene-

cloning technology.

POTENTIALAPPLICATIONS OFSEAFOOD

ENZYMES IN THEDAIRYINDUSTRY

Research has shown that digestive proteases from

fish, due to their specificity, can be useful as rennet

substitutes for calf chymosin in cheese making

(Brewer et al. 1984, Tavares et al. 1997, Shamsuz-

zaman and Haard 1985). Due to their heat lability,

they can be useful for preventing oxidized flavor

from developing in milk (Simpson and Haard 1984).

Simpson and Haard (1984) found that cod and

bovine trypsin are equally effective in preventing

copper-induced off-flavors from developing in milk.

But the cod enzyme has the advantage of being com-

pletely inactivated after pasteurization at 70°C for

45 minutes, whereas 47% of the bovine trypsin is

still active. These studies show that cold-adaption

properties of marine enzymes can be an advantage

in the processing of different foods.