Fish components and preservation

1. Major and minor constituents of fish
Proteins
• Enzymes
Fats
• PUFA
• EFA
• Phospholipids
Vitamins
Minerals
Carbohydrates

2. Proteins
• Herbivorous and lean fish-has high protein content.
• Fish muscle – 15-25% protein.
• Has mainly- Albumin (16-22%),
Contractile proteins (75%)
Collagen and Elastin (3%)
Enzymes: Amylase, Lipases, thiaminase, ATPase, ChE,
Nucleases, glycogenase.

3. Fats
• Fat depot: muscles, head tissue, milt, roe,
liver, skeletal tissue, sub-cutaneous tissue,
viscera. Liver is the main site.
• Quantity of fat decides quality of fish.
• On the basis of fat contents:
Oily or Fatty fish (fat > than 8%)
Average Fatty fish (1-8%)
Lean Fish (< 1%).

4. • High content of PUFA.
• Contain more Omega -3 than 6 and 9.
• Essential Fatty acids: Oleic acid, Linoleic acid
and linolenic acid.
• Phospholipids-0.7%: Lecithins predominates
(50-60%) and sphingomylein and Cephalins
are also found.

5. Vitamins
• Good source of Vit A, D E and B-complex.
• Fish liver oil constitute Vit-A.
• Vit A reaches fish from carotene which is abundant in
planktons. Carotene α, β, γ and Cryptoxanthine give
rise to Vit-A. β carotene is most potent.
• Vit A is abundant in dog, Tuna, hag fish, Hammer
headed shark.
• Vit- D in abundant in liver oils in Cod, Salmon, Tuna,
Sardine, Herring and halibut. Less the oil content of
liver, greater is the Vit-D content.
• Vit-E is present is fish liver oils for protection against
Vit-A oxidation.
• Vit-B complex- acts as co-enzymes, rich in Marine
fishes and in muscles of Pomfret, Magur.

6. Minerals
• Minerals are concentrated in hard parts: scales,
bones, otoliths.100 gm of protein flesh has :
Ca(0.109), Mg (0.133), K (1.671), Phosphorus
(1.148), sulphur (1.119) and Fe (0.0055) gm.
• Other muscle constituent in fish muscles are:
Cu, Mn, St, Zn, Al, Pb, Mo, Fl, I, Co, Cr, Ag, Hg, Si,
Br.
Carbohydrates:
Negligible. Glycogen rapidly converted to lactic
acid

7. Post-Mortem changes in fish
• Post mortem: the changes occuring in time
following death.
• Rigor mortis: stiffness of body after death
(sets within 7 hrs of death of fish).
Causes of rigor mortis:
Due to sustained contraction of transverse
skeletal muscles, brought by some
biochemical and physiological changes in
dying muscles

8. • Anaerobic oxidation of glucose→lactic acid→
promotes actin-myosin combination and ATP
hydrolysis. Muscle fibres shrink and rogor mortis sets
in, resulting in change in muscle texture.
• ATP production falls to zero within 6-8 hrs which is
the cause of rigor mortis. ATP provided softening
effect in live fish because Ca are bound to it. With
the loss of ATP, Ca are released and this promotes
contraction of fibrils.
• Lactic acid accumulates in muscles and pH ↓ to 6.5
to 5.4. lower pH induces contraction in muscle fibrils
and inhibition of muscle capacity of water binding.

9. • The accumulation of lactic acid and autolytic
changes causes-tendering of flesh. The acidity
is imp for prolonged Rigor mortis and also the
suppression of future microbial spoilage.
Factors responsible for prolonged rigor mortis
Lowering of temp (Icing or freezing)
Mode of packing or storage: slaughtered fish
delay onset of rigor than asphyxiated.
Mode of fishing: kind of gear which exhaust the
fish

10. Post-rigor spoilage
Chemical
changes
Microbial
attacks

11. Chemical
changes
Rancidity Autolysis

12. Rancidity
• Unpleasant smell or taste through
decomposition.
• Oxidative rancidity: rancidity occurs due to rapid
oxidation of lipids.
• The lipid molecule undergo rapid oxidation
enhanced by heme protein→ oxidative rancidity.
Fat becomes rusty iron from yellow, oil urns thick
and sticky and smells unpleasant.
• Presence of Chlorides of mg, Ca, Al, Zn in salt
used in fish curing speeds up rancidity.

13. Autolysis
• In autolysis: enzymatic activity speed up the spoilage..
• Accumulation of lactic acid lowers the pH and acidic
pH ruptures the lysosomal membranes, releasing a
number of hydrolytic enzymes like hydrolases,
nucleotidases, proteinases, lipases. The degradd
substrate act as ideal material for microbial growth
and proliferation.
• Proteins→AA →guanine →hypoxanthine →Ammonia
→Carbon-dioxide →volatile basic compounds- render
fish unpalatable.
• ATP →ADP →AMP →IMP →Hypoxanthine →bitter
taste.

14. Microbial spoilage
By Bacteria
As a result of degradation of macromolecules
into smaller molecules, bacterial spoilage sets
in.
Begins with biochemical changes. Bacteria cause
partial digestion of food.
Pathogenic bacteria: E. coli, Streptococci,
Salmonella, Staphylococci and Clostridia.

15. • Clostridium produces powerful toxic
substances, which are lethal for humans. It
grows rapidly in anaerobic conditions and can
survive salt conc. above 6% and cause
botulism.
• Staphylococcus causes milder poisoning
comparatively.

16. By actinomycetes and blue-green algae
• Certain fishes when grown in muddy ponds
may develop ‘Off flavour’ caused by
compound geosmin produced by
actinomycetes and B-G algae (Oscillatoria).

17. Fish Preservation
Principle:
a) Cleaning: with chlorinated or sea water inhibits
spoilage.
b) Low Temp: limits autolysis, enzymatic aitivities
and bacterial growth. At -40 °C, many strains of
bacteria are destroyed leading to storage death.
c) High temp: it has sterilization effects and
destroy the autolytic enzymes. Therefore some
preservation techniques like drying, smoking,
canning are useful.

18. d) Dehydration: to minimize the attack by
moisture loving micro-organisms. The
exposure of fish to high temperature also
minimizes the moisture content.
e) Use of salts: use of excess amount of salt
causes dehydration by osmosis and penetrates
deeply into tissues rendering autolysis
enzymes ineffective. Bacterial growth is also
slowed down.
f) Use of preservatives: drugs and chemicals are
known to have preservative qualities. For eg.

19. • Ascorbic acid: prevents rancidity
• Vinegar: a powerful preservative
• Phelonic compounds in wood smoke: Cresol,
Catechol
• Salicylic acid and Boric acid
• Sodium hypochlorite
• Mixture of sodium acid phosphatase and sodium
benzoate: control red coloration of salted fish.
• Sodium nitrate and sodium chloride: Nitrates used
for freezing
• Antibiotics: prevents microbial spoilage (Aureomycin,
Oxytetracycline, Rimocidin, Chloromycetin, Sorbic
acid.

20. Methods of preservation
1. Icing of fish
2. Freezing
3. Cold storage
4. Drying
Freeze drying
sun drying
Mechanical driers
5. Salting
Dry salting
Wet salting
6. Smoking
Hot smoking
Cold smoking
7. Canning
8. Fish Pickles
9. Fish Pastes

21. I) Icing of the fish
• Fish to Ice= 1:1, depending upon climatic conditions,
length of journey and degree of insulation.
• Thick layer of ice is put at bottom as well as top with
alternate layers of ice and fish in between.
• The total height of fish packed with ice, should not
normally be more than 20 cm.
• Normally crushed ice is used.
• Flake ice is better than crushed but expensive.
• Dry ice is also used for air transport and it does not
melt and used for expensive products.

22. II) Freezing
• By using mixture of ice and salt or refrigeration.
• Liquid nitrogen, Carbon-dioxide are used.
• In India Tunnel/air blast freezers are used-consist
of insulating tunnel, trolleys, and air is blown at -
35 and -40 °C.
• Immersion freezing or brine is a cheaper method.
(fishes are cooled to -1 °C in chilled water, salt is
added to [produce brine, again chilled to -14 °C
and frozen fish are then removed.(disadvantage:
brine penetrates into body).

23. • Frozen fish is subjected to Glazing with water, or
wrapped in a moisture proof wax paper or
cellophane. This layer protects fish fat from
atmospheric oxygen.
Drawbacks of freezing:
• Lead to certain physical and chemical changes.
• Dehydration and dessication of fish results due to
freezing and storage.
• Fat content undergoes oxidation leading to rancidity.
• When water content of tissues gets frozen,
interstitial fluid conc. Increases and it oozes out of
body

24. Cold storage
• Used for storing bulk quantity frozen fish for
longer duration. This fish is then sold as fresh
fish in seasons of scarcity or used for further
processing.
• Normally fish remains edible
1 month stored at -1 °C
4 months stored at -20 °C
8 months stored at -30 °C

25. Drying
I) FREEZE DRYING
Extension of deep freezing when frozen fish at -20 °C is
dried by direct sublimation of ice to water vapor
without any melting into liquid water. This is done by
exposing the fish to 140 °C in a vacuum chamber. The
fish is then packed or canned in dried conditions.
• Only edible parts should be taken.
• Skin has to be removed.
• Precooked fish freeze dry more efficiently than the
raw ones
Drawback: costs are high.

26. II) SUN- DRYING
• Simplest and ancient method
• Practised in India
• Fish are spread in a thin layer on mat and kept in sun
for a day or two.
• Fish are periodically turned over.
• Sometimes fish are dried by hanging on wooden
rods or on open ropes.
Drawback: it is a slow process and results in much loss
through spoilage.
• It develops peculiar cured flavor.
• Oily fish can putrefy.

27. • III) MECHANICAL DRIERS
• To improve the quality and maintain the
nutritive value of fish , dehydration is brought
through driers.
• Hot air dries are used where moisture content
is evaporated by blowing hot air.
• Vacuum drier: application of low temperature
under vacuum.

28. IV) Salting
• It is drying of fish using salt.
• Addition of salt increases osmotic pressure, which
absorbs the moisture content of tissues.
• It brings plasmolysis of bacterial cells.
• Only pure salt should be used.
• Prior to salting gills and other organs are removed.
• Small sized fishes are used as such.
• In Large fishes , many incisions are made for
penetration of salts.
• Considerable large sized fishes are cut into pieces.

29. I) Dry salting
• Sufficient quantity of salt is applied to fishes
and then fish are packed into layers in tub or
cemented tanks and dry salt is sprinkled
between layers.
• Fish are rubbed in salt before packing.
• Salt : fish=1:3 to 1:8 depending on type of fish
(oily fish requires more salt).
• The fish are removed from tub after 10-24 hrs,
washed in brine and dried in sun for 2-3 days.

30. II) Wet drying
First day:
• The fish are gutted, split and cleaned before salting.
• Cleaned fish are packed in large vats containing
concentrated salt solution and stirred daily till properly
pickled. Salt: fish= 1:3
Second day
• Fish are restacked with top layer moved to bottom and
remaining salt is applied.
Third day
• Salt is rubbed and fish are restacked.
Then stacking is left undisturbed for 7-10 days.

31. Smoking
• 3% of flesh is preserved by smoking. Fish is
delicate, succulent, but fish has poor storage
life.
• Smoke is produced by burning woods. The
smoke contains gases, acid vapors and
phenols. Bacteria are destroyed by acid
content. Phenol and phenol derivatives give
characteristic color.
• Hard wood is used.

32. Hot smoking
• Carried out in kilns. Fresh, frozen and chilled fish
can be subjected to hot smoking.
• Fish are washed, salted, excess salt rinsed, then
tied in bundles, fried, cooked and then subjected
to hot smoking inside klins.
• At first temperature is raised to 130 °C and
smoking is done at 40 °C.
• Smoked fish is cooled and then packed.
Cold smoking
38 °C at smokeless fire and then less than 28 °C

33. Canning
• Sealing of sealing the fish inside air-tight cans
and heating under pressure for destroying
bacteria.
• Blanching: fresh fish is first immersed into
cold or hot brine for shrinkage of tissues,
gases will be released, bacterial population
will be reduced and inhibited enzymatic
activity.
• The blanched material is stored in cans