1. Lecture 1
Composition of fish

2.  The fish has a skeletal or cartilaginous structure which
provides support for the body.
 The muscles which form the edible part account for most of
the weight of the fish.
 The skin forms a cover, often with an outer layer of scales,
and secretes a slimy mucus, which lubricates the fish and
seals the surface.
 The gills are the main part of the breathing mechanism and
take up oxygen from the water.
 The organs in the body cavity, including the stomach,
intestine and liver are known as the guts.
 Removal of the guts is normally the first step in handling
and preservation. Shell fish has no backbone, but a hard
outer cover or shell exoskeleton, which gives the necessary
support and protection.

3. Proximate compostion
 The principal components of the fish muscle - water, fat
and protein - must be preserved with little or no changes.
 The protein content is usually in the region of 15-20
percent, whereas the fat content varies widely from
species to species and from season to season. It can be
as low at 0.5 percent in lean starved fatty fish and can
reach over 20 percent in some species.
 In lean fish the bulk of the fat is stored in the liver and not
in the muscle. Water is the main constituent, with
considerable variations, typically 80 percent in lean fish
and 70 percent in fatty fish.
 Carbohydrates, minerals, vitamins and some water
extractable components are examples of other minor
substances present.

4. Water
 Major component 70-80% of the fresh
weight
 Maximum of 90% in Bombay duck
 Essential for all physiological functions
 Water in 2 forms:
 Free and bound water

5.  Moisture content
 Water activity
 Importance of free water
 Inverse relationship between water
and fat content

6. Protein
 Complex structures formed of
aminoacids
 Generally 16-18%, varies with season
and other phenomena like feeding,
spawning etc
 Considered low if below 15%
 Red muscle contains lower levels
compared to light muscle

7. Three types of protein: based on
the solubility in salt solutions
 Sarcoplasmic or enzymatic proteins
 soluble in low ionic strength salt solutions
(<0.15)
 Includes myogen, globulin etc
 Enzymes of muscle metabolism
 25-30% of total protein
 Higher in pelagic fish, lower in demersal
fishes
 Electrophoretic pattern – species
identification

8.  Myofibrillar protein:
 Soluble in high ionic strength solutions
(>05)
 Actin, mysin, actomyosin, tropomyosin
etc
 Contraction and relaxation
 Around 65% of muscle protein in fish
 Determines functional properties
 Gelling, rheological properties
 Useful in surimi industry

9.  Stroma or connective tissue protein:
 Soluble in neutral salt solutions or in
dilute acids or alkalies.
 Constitute around 3% in total in
teleosts
and 10% in elasmobranches.
 Connective tissues of the muscles are
made of this.
 Texture of fish muscle – due to low
content of this protein.

10. Changes in protein
 Denaturation

11. Amino acid composition
 All the common amino acids are present
in fish protein
 Fish protein - contains all the essential
aminoacids in good proportions
 Rich in lysine
 Low in tryptophan
Definition:
 Essential amino acid
 Limiting amino acid
 Complete protein

12. Essential Amino Acids
 An essential amino acid or indispensable
amino acid is an amino acid that cannot be
synthesized de novo by the organism (usually
referring to humans), and therefore must be
supplied in the diet.
 Isoleucine, leucine, lysine, methionine, phenylala
nine, threonine, tryptophan, and valine—must be
obtained from the diet.
 (In addition, adults are capable
of synthesizing arginine and histidine, but these
amino acids are believed to be essential to
growing children, meaning that children cannot
produce them on their own.)

13. Complete protein
 A complete protein is one that contains all of the
essential amino acids in quantities sufficient for
growth and repair of body tissue.
 Most proteins from animal sources contain all the
essential amino acids and are therefore
considered complete proteins.
 On the other hand, many plant proteins do not
contain all of the essential amino acids.
 For example, lysine is absent from corn, rice, and
wheat, whereas corn also lacks tryptophan and
rice lacks threonine. Soybeans are lacking
in methionine.

14. Limiting amino acids
 Our bodies use amino acids in a specific ratio
to each other, so if a person doesn’t get
enough of one of them to match with the rest,
the rest can only be used at a level to
balance with that low one.
 These are called limiting amino acids,
because if a person’s diet is deficient in one
of them, this will limit the usefulness of the
others, even if those others are present in
otherwise large enough quantities.
 The three limiting amino acids include the
sulfur-containing ones (methionine and
cysteine), tryptophan, and lysine.

15. Fat
 Fatty acid complexes
 Extractable by solvents
 Type of compounds are fatty acids,
glycerides, phospho glycerides,
sphingo lipids, aliphatic alcohols,
waxes, steroids etc.
 Triacylglycerols – major constituent in
lipids
 0.5-18% lipid content range in fish

16.  Fluctuation in lipid content in fish
 Lipid storage in fish
 Lean fish – Liver
 Fatty fish – Muscle
 Storage lipid – liver, adipose tissue,
mainly triacylglycerol
 Phospho lipids – cell membarne
components
 Permeability o cell membranes, transport
of fluids etc.

17.  Dark muscle and white muscle lipid
composition
 Distribution of lipid – not uniform
 More towards head region

18. Fatty acid composition
 Poly unsaturated
 More double bonds
 Even number of carbon atoms
 Changes in fatty acid composition
 Saturated – Myristic, Palmitic and
stearic
 MUFA – Palmitoleic, oleic
 PUFA – Arachidonic, EPA, DHA

19. Changes in lipid
 Hydrolysis – by lipases
 Oxidation
Lipid oxidation
 Initiation
 Propagation
 Termination
 Free radicals, contact with
oxygen, catalysts like copper or iron

20.  Primary products – hydro peroxides
 Secondary products – aldehydes and
ketones, alcohols and carboxylic acids
 Rancid flavour and rancid fishy smell
Anti oxidants:
 Natural and synthetic
 Vit E, BHA, BHT, PG
 0.1-0.2%

21. Vitamins
 Water and fat soluble
 More fat sol. Vit A, D, E in fish than in
meat
 Rich in Vit B
 Liver oils – good source of vitamins
 Cod liver oil – Vit D
 Shark liver oil – Vit A

22. Minerals
 Calcium
 Sodium
 Potassium
 Phosphorous
 Magnesium
Elements of Nutritional significance are
 Calcium, Iodine, Fluoride

23. Summon up