16 Biochemistry of Seafood Processing 371amino acids. This permits the marinade to create the
proper flavor and texture in the product (Meyers
1965).
Smoke curing means the smoking of presalted
fish. The action of the smoke constituents produces
a unique smoky odor, taste, and color. The process
also contributes to the tenderizing action on the
fish tissue. In cold-smoked fish, this tenderization is
caused predominately by the action of endogenous
proteolytic enzymes because of their activity at such
ambient temperatures.
BIOCHEMISTRY OF THERMAL-
PROCESSED PRODUCTS
Exposure of the fish to elevated temperatures is
detrimental to tissue structure, and results in very
undesirable effects (Haard 1994). Extreme texture
softening in fish was believed to be the result of cys-
teine protease acting on the fish muscle at elevated
temperatures (Konegaya 1984). Heat-stable alka-
line proteases and neutral proteases (modori or gel-
degradation) are active when the temperature reach-
es 60–70°C (Lin and Lanier 1980, Kinoshita et al.
1990). Degradation of connective tissue of mackerel
appears to be associated with muscle proteases and
pyloric ceca collagenase (Pan et al. 1986).
The rate of oxidation of desirable myoglobin and
oxymyoglobin of the red muscles of tuna to brown
metmyoglobin depends on the species of the fish and
on the storage temperature (Mattews 1983). Color
deterioration in iced and frozen stored bonito, yel-
lowfin, and skipjack tuna caught in Seychelles wat-
ers was demonstrated in this study.
Food biochemistry plays a role in the production
of thermally processed seafood. During the canning
of seafood, it is a common practice to precook the
raw materials, for example, fish and crustaceans. The
accompanying thermal treatment coagulates the pro-
teins in the muscles for easy handling and removal of
nonedibles as well as for quality inspection in the lat-
er steps. It also inactivates the enzymes that can
cause biochemical deterioration of the raw materials,
when exposed to elevated temperatures and extended
storage times. For example, in manufacturing canned
tuna, the fish is precooked and permitted to cool
completely, sometimes overnight, before the follow-
ing steps: (1) removal of skin, bones, dark meats, and
viscera and (2) inspection for the presence of defects,
e.g, honeycombed and/or burnt tissues.
It should be noted that honeycombed tissues are
only detectable in the cooked fish. In the production
of canned crabmeat, the precooked crab is cooled be-
fore the extraction of crabmeat. Without precooking
to coagulate the crabmeat, it is almost impossible to
separate the crabmeat from its shell efficiently. The
precooking also inactivates those enzymes that can
degrade the quality of the product. This is especially
important in products like crab and shrimp, as the
deteriorating enzymes can act very quickly on these
tissues at elevated temperatures. However, there are
exceptions where the raw fish is not precooked in
order to preserve the premium quality. This includes
the production of canned salmon, where sections of
raw salmon with skin and bones are stuffed into the
can before sealing and processing.
Thermal processing such as mild heating also
is applied in the production of some dried seafood
products such as fish, shrimp and squid. The heating
process inactivates the deteriorating enzymes in the
raw materials. This stops the enzymatic reactions
from occurring during drying or dehydrating pro-
cesses that expose the intermediate products to am-
bient or elevated temperatures for extended periods.
For example, in the production of dried, shaved bon-
ito, the raw bonito is first precooked in brine before
the processes of recovery of loin tissues, drying to
coagulate the tissues, and shaving of the dried prod-
uct. Without this precooking process, the fish tissue
will deteriorate during the long drying process. For
dried shrimp, the majority of the product is pro-
duced with the precooking process to inactivate the
deteriorating enzymes before drying or dehydrating.
However, a small amount of dried shrimp is pro-
duced without precooking to produce specialty prod-
ucts. For dried squid, it is usually produced without
precooking to develop the unique flavor from enzy-
matic reactions during drying or dehydration. How-
ever, a small amount is produced by precooking the
product prior to the drying process.
Thermal processing of seafood such as canning
and mild heat treatment attempts to produce a final
product with long shelf life and favorable consumer
acceptance. For more details, refer to the review by
Aubourgh (2001).REFERENCES
Alasalvar C, Taylor T. 2002. Seafoods—Quality, Tech-
nology and Nutraceutical Applications. Berlin/New
York: Springer. 224 pp.