Lecture 8. fish ocmponents 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
- 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