Food Biochemistry and Food Processing

352 Part III: Muscle Foods

techniques including canning, freezing, and dehydra-
tion.
The nutritive value of seafood is well known for
its content of protein and some minerals and, recent-
ly, its fat quality. For the past 20 years considerable
attention has been paid to the content of polyunsatu-
rated omega-3 fatty acids in fish, especially their
prevalence in fatty fish. Of course, one must not for-
get the relatively high levels of cholesterol in some
fish and shellfish, especially crustaceans and squid.
The biochemical changes in macronutrients of sea-
food are of interest to nutritionists, food processors,
and consumers. Their importanc in public health can-
not 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 pre-
servation. The biochemical aspects of seafood will
be studied using the following approaches:

• Glycogen in seafood.Biochemical changes in its
  glycogen, which exists in small quantities,
  initiates the biochemical 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 sarcoplasmic, myofibrillar,
  and stromal protein. This discussion is
  accompanied by a brief mention of nonprotein
  nitrogenous substances.


• 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. Such
  biochemical changes in seafood’s protein and
  nonprotein components usually reduce its
  economic value and may also create safety
  problems.


• Pigments in seafood.Biochemical changes will
  be discussed with reference to epithelial
  discoloration, hemoglobin, hemocyanin,
  myoglobin, carotenoids, and melaninosis.


• 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 formation, free fatty acid

accumulation, and tyrosine accumulation.

• Processing methods for seafood.In the last 25
  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

ATTRIBUTES

As mentioned earlier, seafood is nutritious. It con-

tains nutrients, some of which are essential to human

health. The nutrients are divided into two groups:

macronutrients and micronutrients. This first section

covers the macronutrients (water, protein, lipids)

and their changes during processing and preserva-

tion. This is followed by a discussion of the micro-

nutrients (vitamins and minerals). The implications

of undesirable metals in seafood are then discussed.

Issues related to health attributes in seafood are pre-

sented last.

COMPOSITION

Macronutrients

The macronutrients found in seafood include protein,

fats and oils, and water. All other nutrients found in

seafood are considered 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, are devoid of carbo-

hydrates. The amount of protein is similar in pelagic

and demersel fish. However, pelagic fish, commonly

called fatty fish, are higher in lipids (9–17 g/100 g)

than demersal fish that live on 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 pro-