Major and minor constituents of fish

Proteins• EnzymesFats• PUFA• EFA• PhospholipidsVitaminsMinerals Carbohydrates

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.

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%).

• 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 Cephalinsare also found.

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 giverise to Vit-A. β carotene is most potent.

• Vit A is abundant in dog, Tuna, hag fish, Hammerheaded shark.

• Vit- D in abundant in liver oils in Cod, Salmon, Tuna,Sardine, Herring and halibut. Less the oil content ofliver, greater is the Vit-D content.

• Vit-E is present is fish liver oils for protection againstVit-A oxidation.

• Vit-B complex- acts as co-enzymes, rich in Marinefishes and in muscles of Pomfret, Magur.

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

Post-Mortem changes in fish

• Post mortem: the changes occuring in timefollowing 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 transverseskeletal muscles, brought by somebiochemical and physiological changes indying muscles

• Anaerobic oxidation of glucose→lactic acid→promotes actin-myosin combination and ATPhydrolysis. Muscle fibres shrink and rogor mortis setsin, resulting in change in muscle texture.

• ATP production falls to zero within 6-8 hrs which isthe cause of rigor mortis. ATP provided softeningeffect in live fish because Ca are bound to it. Withthe loss of ATP, Ca are released and this promotescontraction of fibrils.

• Lactic acid accumulates in muscles and pH ↓ to 6.5to 5.4. lower pH induces contraction in muscle fibrilsand inhibition of muscle capacity of water binding.

• The accumulation of lactic acid and autolyticchanges causes-tendering of flesh. The acidityis imp for prolonged Rigor mortis and also thesuppression of future microbial spoilage.

Factors responsible for prolonged rigor mortis

Lowering of temp (Icing or freezing)

Mode of packing or storage: slaughtered fishdelay onset of rigor than asphyxiated.

Mode of fishing: kind of gear which exhaust thefish

Post-rigor spoilage

Chemical changes

Microbial attacks

Chemical changes

Rancidity Autolysis

Rancidity• Unpleasant smell or taste through

decomposition.

• Oxidative rancidity: rancidity occurs due to rapidoxidation of lipids.

• The lipid molecule undergo rapid oxidationenhanced by heme protein→ oxidative rancidity.Fat becomes rusty iron from yellow, oil urns thickand sticky and smells unpleasant.

• Presence of Chlorides of mg, Ca, Al, Zn in saltused in fish curing speeds up rancidity.

Autolysis

• In autolysis: enzymatic activity speed up the spoilage..

• Accumulation of lactic acid lowers the pH and acidicpH ruptures the lysosomal membranes, releasing anumber of hydrolytic enzymes like hydrolases,nucleotidases, proteinases, lipases. The degraddsubstrate act as ideal material for microbial growthand proliferation.

• Proteins→AA →guanine →hypoxanthine →Ammonia→Carbon-dioxide →volatile basic compounds- renderfish unpalatable.

• ATP →ADP →AMP →IMP →Hypoxanthine →bittertaste.

Microbial spoilage

By Bacteria

As a result of degradation of macromoleculesinto smaller molecules, bacterial spoilage setsin.

Begins with biochemical changes. Bacteria causepartial digestion of food.

Pathogenic bacteria: E. coli, Streptococci,Salmonella, Staphylococci and Clostridia.

• Clostridium produces powerful toxicsubstances, which are lethal for humans. Itgrows rapidly in anaerobic conditions and cansurvive salt conc. above 6% and causebotulism.

• Staphylococcus causes milder poisoningcomparatively.

By actinomycetes and blue-green algae

• Certain fishes when grown in muddy pondsmay develop ‘Off flavour’ caused bycompound geosmin produced byactinomycetes and B-G algae (Oscillatoria).

Fish Preservation

Principle:

a) Cleaning: with chlorinated or sea water inhibitsspoilage.

b) Low Temp: limits autolysis, enzymatic aitivitiesand bacterial growth. At -40 °C, many strains ofbacteria are destroyed leading to storage death.

c) High temp: it has sterilization effects anddestroy the autolytic enzymes. Therefore somepreservation techniques like drying, smoking,canning are useful.

d) Dehydration: to minimize the attack bymoisture loving micro-organisms. Theexposure of fish to high temperature alsominimizes the moisture content.

e) Use of salts: use of excess amount of saltcauses dehydration by osmosis and penetratesdeeply into tissues rendering autolysisenzymes ineffective. Bacterial growth is alsoslowed down.

f) Use of preservatives: drugs and chemicals areknown to have preservative qualities. For eg.

• 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 sodiumbenzoate: control red coloration of salted fish.

• Sodium nitrate and sodium chloride: Nitrates usedfor freezing

• Antibiotics: prevents microbial spoilage (Aureomycin,Oxytetracycline, Rimocidin, Chloromycetin, Sorbicacid.

Methods of preservation

1. Icing of fish

2. Freezing

3. Cold storage

4. Drying

Freeze drying

sun drying

Mechanical driers

5. SaltingDry saltingWet salting

6. SmokingHot smokingCold smoking

7. Canning8. Fish Pickles9. Fish Pastes

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 withalternate layers of ice and fish in between.

• The total height of fish packed with ice, should notnormally 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 notmelt and used for expensive products.

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-consistof 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 isadded to [produce brine, again chilled to -14 °Cand frozen fish are then removed.(disadvantage:brine penetrates into body).

• Frozen fish is subjected to Glazing with water, orwrapped in a moisture proof wax paper orcellophane. This layer protects fish fat fromatmospheric oxygen.

Drawbacks of freezing:

• Lead to certain physical and chemical changes.

• Dehydration and dessication of fish results due tofreezing and storage.

• Fat content undergoes oxidation leading to rancidity.

• When water content of tissues gets frozen,interstitial fluid conc. Increases and it oozes out ofbody

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

Drying

I) FREEZE DRYING

Extension of deep freezing when frozen fish at -20 °C isdried by direct sublimation of ice to water vaporwithout any melting into liquid water. This is done byexposing the fish to 140 °C in a vacuum chamber. Thefish 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 theraw ones

Drawback: costs are high.

II) SUN- DRYING

• Simplest and ancient method

• Practised in India

• Fish are spread in a thin layer on mat and kept in sunfor a day or two.

• Fish are periodically turned over.

• Sometimes fish are dried by hanging on woodenrods or on open ropes.

Drawback: it is a slow process and results in much lossthrough spoilage.

• It develops peculiar cured flavor.

• Oily fish can putrefy.

• 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.

IV) Salting

• It is drying of fish using salt.

• Addition of salt increases osmotic pressure, whichabsorbs 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 forpenetration of salts.

• Considerable large sized fishes are cut into pieces.

I) Dry salting

• Sufficient quantity of salt is applied to fishesand then fish are packed into layers in tub orcemented tanks and dry salt is sprinkledbetween 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.

II) Wet dryingFirst 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.

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.

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 subjectedto hot smoking inside klins.

• At first temperature is raised to 130 °C andsmoking is done at 40 °C.

• Smoked fish is cooled and then packed.Cold smoking38 °C at smokeless fire and then less than 28 °C

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