BLBS102-c19 BLBS102-Simpson March 21, 2012 13:33 Trim: 276mm X 219mm Printer Name: Yet to Come
19 Biochemistry of Seafood Processing 359textural and sensory properties of frozen seafood. Therefore,
it is important to understand the mechanisms of various
biochemical and physicochemical reactions occurring during
freezing and frozen storage so that the quality of frozen food
can be maintained.BIOCHEMISTRY OF DRIED,
FERMENTED, PICKLED, AND
SMOKED SEAFOODSalting, fermenting, marinating (pickling), drying, and smoking
of fish and marine invertebrates increase the shelf life and de-
velop in the products’ desirable sensory properties. Extension of
storage life is achieved mainly through the combined effects of a reduction in water activity from the addition of salt;
a decrease in microbial load by the application of heat;
the presence of inherent preservatives such as acetic acid;
the use of chemical preservatives such as ascorbic acid,
BHA, and BHT; and
the antibacterial and antioxidant activities of various smoke
components.The enzymatic and spoilage processes are controlled not only
by these chemical components but also by the temperature, pH,
and availability of oxygen. Desirable changes in sensory prop-
erties are thus developed as a result of these carefully controlled
chemical and enzymatic processes (Shewan 1944, Doe and
Olley 1990, Miler and Sikorski 1990, Shenderyuk and Bykowski
1990, Perez-Villarreal 1992, Fuke 1994, Haard 1994, Sikorski
and Ruiter 1994).
There are some changes in proteins. In the salting of fish, salt
will penetrate slowly into the tissues, affecting the stability of the
native proteins and reducing their extractability. Heavily salted
fish, when compared with less salted fish, has the following
disadvantages: More water loss due to osmosis
Tougher texture
Less developed flavorIt should be remembered that enzymes are also proteins, and
their activities are affected by salt concentration.
Another effect of salting is the changes in texture of the final
product. It is believed that the calcium and magnesium ions
present as impurities in salt may penetrate the fish, giving rise
to a soft, “mushy” texture in the fillet. This may be undesirable
for most salted fish, but this effect is considered highly desirable
in some Chinese salted products (tender salted threadfin, tender
salted mackerel, and others), and Scandinavian products (such
as kryddersild, tidbit, and gaffelbiter) (Shewan 1944). Salting of
whole fish should be controlled precisely, as overripening will
result in excessively soft products with sensory properties that
are undesirable to most consumers. However, changes in salted
fish fillets depend mostly on endogenous muscle proteases.
Fermented fish paste and sauce are popular products prepared
and consumed in southern China and Southeast Asian countries
as a source of nutrients and as condiments. Generally, whole fishor shrimp are used as the raw materials for the preparation of
these products. It is believed that extensive proteolysis occurs
under carefully controlled conditions. It is difficult to differenti-
ate the endogenous and bacterial actions of proteolysis because
of the use of whole fish or shrimp and the way these products are
produced. Sikorski and Ruiter (1994) summarized some of the
work on proteolysis in fermented fish products. Cathepsins A
and C as well as trypsin-like enzyme are endogenous proteases
that appear to contribute to fish sauce production both in yield
and quality (Orejana and Liston 1982, Rosario and Maldo 1984,
Raksakulkthai et al. 1986).
Chiou et al. (1989) reported that cathepsin D-like and
aminopeptidase activities release a large amount of free amino
acids during roe processing and contribute to the flavor. In the
drying of squid, endogenous cathepsin C appears to contribute
to desirable qualities (texture and flavor) of traditional products
(Haard 1983). Simpson and Haard (1984) reported that added
trypsin appears to be a key enzyme contributing to the texture
and flavor of matjes herring.
Marinating fish (mainly herring) by means of salt and acetic
acid is one of the oldest ways of preserving food in European
countries. The acid condition of the marinades, with pH 4–4.5,
makes the tissue cathepsins much more active. This results in the
degradation of muscle proteins into peptides and amino 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 ac-
tion 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
PRODUCTSExposure of the fish to elevated temperatures is detrimental to
tissue structure, and results in very undesirable effects (Haard
1994). Extreme texture softening in fish has been attributed to
cysteine proteases acting on the fish muscle at elevated tem-
peratures (Konegaya 1984). Heat-stable alkaline proteases and
neutral proteases (modori or gel-degradation) are active when the
temperature reaches 60–70◦C (Lin and Lanier 1980, Kinoshita
et al. 1990). Degradation of connective tissue of mackerel ap-
pears to be associated with muscle proteases and pyloric ceca
collagenase (Pan et al. 1986).
The rate of oxidation of desirable myoglobin and oxymyo-
globin of the red muscles of tuna to brown metmyoglobin de-
pends on the species of the fish and on the storage temperature
(Mattews 1983). Color deterioration in iced and frozen stored
bonito, yellowfin, and skipjack tuna caught in Seychelles waters
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,