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19 Biochemistry of Seafood Processing 345includes awareness of its health benefits. Thus, when processing
seafood, it is important to understand the scientific and technical
reasons that are responsible for the sensory and health attributes
of seafood, in addition to how the manufacturing process can
affect the basic quality of seafood. The same knowledge may
lead to a reduction in the perishability of seafood, a problem
that has existed since the beginning of time, though it has been
partially solved by many modern techniques including canning,
freezing, and dehydration.
The nutritive value of seafood is well known for its con-
tent of protein and some minerals and, recently, its fat qual-
ity. For the past 20 years, considerable attention has been paid
to the content of polyunsaturated omega-3 fatty acids in fish,
especially their prevalence in fatty fish. Of course, one must
not forget the relatively high levels of cholesterol in some fish
and shellfish, especially crustaceans and squid. The biochemical
changes in macronutrients of seafood are of interest to nutrition-
ists, food processors, and consumers. Their importance in public
health cannot be overestimated if one considers how seafood
contributes to the nutrition and health of the human body. A
short discussion of the nutritive values of fish serves as an
introduction.
Perishability of seafood is important economically as well as
for its safety. The price of seafood can drop drastically if it is not
handled properly and is handled without refrigeration or other
forms of preservation. The biochemical aspects of seafood will
be discussed in this chapter using the following approaches: Glycogen in seafood: Biochemical changes in its glycogen,
which exists in small quantities, initiates the biochemi-
cal process, in the same way that it occurs in other animal
products.
Nitrogenous compounds in seafood: The degradation of
protein will be discussed, with a special reference to sar-
coplasmic, myofibrillar, and stromal protein. This dis-
cussion is accompanied by a brief mention of nonpro-
tein nitrogenous substances. Such biochemical changes
in seafood’s protein and nonprotein components usu-
ally reduce its economic value and may also create safety
problems.
Lipids in seafood: Fat can undergo many biochemical
changes, both qualitatively and quantitatively. Some
changes can cause rancidity, especially during the storage
of fatty fish.
Pigments in seafood: Biochemical changes will be
discussed with reference to epithelial discoloration,
hemoglobin, hemocyanin, myoglobin, carotenoids, and
melanosis.
Quality indices in seafood: The monitoring of the quality of
seafood has been the subject of intense scientific research.
Currently, the techniques available are lactic acid formation
with lowering of pH, nucleotide catabolism, degradation of
myofibrillar proteins, collagen degradation, dimethylamine
(DMA) formation, free fatty acid (FFA) accumulation, and
tyrosine accumulation.
Processing methods for seafood: In the last 30 years, great
advances have taken place in the processing of seafood.The basic observation is simple. No matter what method is
used or invented to process the products, their biochemistry
is affected. Three types of processing techniques will be
discussed in this chapter: freezing, drying, and heating.When studying this chapter, the reader should refer to Chapter
1 of this book for more details on food biochemistry.NUTRITIVE COMPOSITION OF THE
MAJOR GROUPS OF SEAFOOD AND
THEIR HEALTH ATTRIBUTESAs mentioned earlier, seafood is nutritious. It contains nutrients,
some of which are essential to human health. The nutrients are di-
vided into two groups: macronutrients and micronutrients. This
first section covers the macronutrients (water, protein, lipids)
and their changes during processing and preservation. This is
followed by a discussion of the micronutrients (vitamins and
minerals). The implications of undesirable metals in seafood are
then discussed. Issues related to health attributes in seafood are
presented last.CompositionMacronutrientsThe macronutrients found in seafood include protein, fats and
oils, and water. All other nutrients found in seafood are consid-
ered micronutrients and are of minor significance. Fish contains
63–84% water, 14–24% protein, and 0.5–17% lipid by weight.
Fish, like other muscle sources of protein, have only small
amounts of carbohydrates (as muscle glycogen). The amount of
protein is similar in pelagic and demersal fish. However, pelagic
fish, commonly called fatty fish, are higher in lipids (9–17 g/100
g) than demersal fish that live at the bottom of the ocean (0.3–1.6
g/100 g).
The primary source of fish protein is muscle, and the protein
quality is comparable to other animal protein from milk, eggs,
and beef. Muscle from fish and shellfish has very little connective
tissue and is readily hydrolyzed upon heating, resulting in a
product that is tender and easy to chew.
The forms of lipid in fish are triglycerides or triacylglycerols.
Triglycerides in pelagic fish contain the long-chain polyunsatu-
rated fatty acids (PUFAs) 20:5v3 eicosapentoic acidand 22:6v3
docosahexanoic acid (DHA), which have many health benefits
including normal development of the brain and retina in infants
and prevention of heart diseases in adults.
Pelagic fish store lipids in the head and muscle, whereas lipids
in demersal fish are stored primarily in the liver and peritoneal
lining and under the skin, except in halibut, which has both liver
and muscle stores. The lipid content of pelagic fish varies with
the season, feeding ground, water salinity, and spawning. Fish do
not feed during spawning but depend on lipid stores for energy.
For example, the lipid content of salmon may be 13% when the
salmon begins traveling upstream to spawning grounds in the
spring and only 5% at the end of the spawning season in the fall.
Herring show more seasonal variation in lipid content, with a
peak level of 20% in the spring, which drops to 10–15% during