Spoilage of fish-process and its prevention
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Spoilage Of Fish-Process And Its Prevention

Prabjeet Singh, Mohd Danish and Amita Saxena

Department of Fishery Biology, College of Fisheries,

G.B.Pant University of Agriculture and Technology, Pantnagar, Uttrakhand, India

Correspondence : prabjeet29255@yahoo.co.in


The foods are usually classified as less perishable, moderately perishable and highly perishable in order to understand their perishable nature. Cereals, nuts and grains are included in less perishable and more stable category, vegetables as moderately perishable and seafood's as highly perishable food items. Seafood's are less stable because of their high moisture content and availability of nutrients for the growth of microorganisms. Ambient temperature plays a crucial role to alter the stability of a product. Highly perishable foods like seafood's have low tolerance to ambient temperature, while moderately perishable items like fruits and vegetables have increased tolerance and non perishable items are least affected.


Causative factors of spoilage

Spoilage and freshness are the two qualities that have to be clearly defined. A fresh product is defined as the one whose original characters remain unchanged. Spoilage therefore is the indicative of post harvest change. This change may be graded as the change from absolute freshness to limits of acceptability to unacceptability. Spoilage is usually accompanied by change in physical characteristics. Change in colour, odour, texture, colour of eyes, color of gills and softness of the muscle are some of the characteristics observed in spoiled fish. Spoilage is caused by the action of enzymes, bacteria and chemicals present in the fish. In addition, the following factors contribute to spoilage of fish.


  • High moisture content

  • High fat content

  • High protein content

  • Weak muscle tissue

  • Ambient temperature

  • Unhygienic handling

Process of spoilage

Fish is highly nutritive. It is tasty because of its constituents. The main components of fish are water, protein and fat. The spoilage of fish is a complicated process brought about by actions of enzymes, bacteria and chemical constituents. The spoilage process starts immediately after the death of fish. The process involves three stages:

  1. Rigor mortis

  2. Autolysis

  3. Bacterial invasion and putrefaction

Enzyme action

The Rigor mortis is a physical effect on the muscle tissue of fish caused by chemical changes following the death. In live fish, its movements are controlled by chemical signals which cause the eythmic contraction (stiffing) and relaxation of the muscles. This produces swimming action. After the death, the normal circulatory system breaks down and chemical signals leak into the muscle causing them to stiffen. This process is known as Rigor Mortis. In other words, in live fish the glycogen present in the muscle is converted to carbon dioxide and water after supply of oxygen to the cells. After the death of fish, the blood circulation stops and the supply of oxygen is prevented. The enzymes present in the muscle convert glycogen into lactic acid. The pH of the fish muscle falls. The formation of the lactic acid continues till the supply of glycogen is completely used up.

After the completion of rigor mortis, muscle stiffness gradually decreases accompanied by increase in pH, ending up in softening of muscle. This is followed by breakdown of proteins by enzymes. This process is called as autolysis.

Thus autolysis can be described as an internal breakdown of the structure of the protein and fats due to a complex series of reactions by enzymes. Autolysis of protein starts immediately after rigor and creates favorable conditions for the growth of bacteria.

Another important action of the enzymes is that it affects the flavor of fish. The components responsible for the taste and flavor of the fish are changed by the enzymatic action. An example is the progressive, degradation of ATP to AMP and Hypoxanthine. Hypoxanthine is produced by the breakdown of ATP which is a main component of fish muscle nucleotide. The accumulation of Hypoxanthine imparts a bitter taste in the fish muscle accompanied by loss of fresh fish flavor. Thus the estimation of Hypoxanthine content in fish indicates the degree of freshness.

Enzymatic action also causes decomposition in the fish known as belly bursting. The belly bursting is caused by the action of digestive enzymes present in the gut of the fish.

The black spot formation in shrimps is also caused by the action of the enzymes on the amino acid. The black colour is due to the formation of Melanin (Black Pigment
) by the action of enzyme tyrosinase on tyrosin present in the shrimps. Black spots present a poor appearance and therefore, are not acceptable.


Action of the Bacteria

The freshly caught fish will be almost free from bacteria but the surface slime, gills and intestine may contain considerable load of bacteria. When the fish is dead, these bacteria start attacking the flesh causing spoilage and produce undesirable compounds. The nature and type of bacteria present in a fish depends upon the water from where it is caught and methods used for handling of the fish after its catch. The important changes brought out by the action of the bacteria in fish are as follows.

i) Reduction of TMAO to TMA

Marine fish contains a small percentage of odourless TMAO which is reduced to an offensive smelling TMA by the action of bacteria.

ii) Breakdown of Amino Acids and formation of Primary Amines

The bacterial action of amino acids present in the fish muscle leads to formation of primary amines. Examples are formation of histamine from histidine, arginine from glutamic acid etc. This bacterial action may cause food poisoning in extreme cases.

iii) Breakdown in Urea

The high concentration of urea in the flesh of some fishes is degraded to ammonia by the microorganisms. The formation of ammonia is accompanied by an offensive odour.


Chemical Action

The most common chemical action which causes spoilage is the oxidative rancidity in fatty fishes. The levels of peroxide value and free fatty acid content both a measure of oxidative rancidity are considered an index of quality of fat fishes.

The spoilage in fish is accompanied by the change in physical characteristic. Changes in color, texture, odour, color of eyes, color of gills, softness of muscle, belly bursting are some of the characteristics of spoiled fish.


Prevention/Reduction of Spoilage.


The spoilage of fish is caused by enzymatic, bacterial and chemical action. The activity of organism can be controlled, reduced or even retarded by proper handling and immediate lowering of the temperature. The chilling of the fish immediately after catch and holding the fish at 0 oC by proper icing will reduce the spoilage. In case of shrimps, removing head immediately after catch will reduce the rate of spoilage. In the case of big fishes, beheading and eviscerating will reduce the enzymatic actions which cause spoilage.

The spoilage is reduced or prevented in a number of ways like drying, salting, chilling, canning and freezing. Chilling is a means of short term preservation of seafoods achieved by the reduction in temperature using ice. Freezing is the most satisfactory method currently available for a long term preservation of seafood. It is, in fact by far the best way of preventing fish from spoilage, since fish continues to remain in almost the same natural conditions even after freezing. It is effective for retaining flavour, colour and nutritive value of seafoods. Freezing is a process by which the water in the fish muscle is crystallized into ice. The crystallization will be complete at -40 oC.

After freezing, the fish must be stored at a temperature maintained constantly at -18 oC or below. Fluctuation in this temperature will cause spoilage of products. If there is a wide variation in the temperature recrystallisation takes place. Dehydration is another important reaction of a physical nature caused by the evaporation of ice due to differences in vapour pressure over the product surface and in the air of the store room. Loss of the moisture by evaporation of ice causes the product surface to dry resulting in dull appearance and even discolouration in some cases. The evaporated water eventually condenses and freezes on the cooling surfaces of the store room and the transfer of moisture from the product will be continuous. Proper glazing and packaging eliminates this evaporation.


Conclusion

Preparation of material for freezing is an important process requiring intelligent skill, extreme precaution and careful operations. The spoilage process can be controlled to a large extent by observing good manufacturing practices. The most important steps involved in the good manufacturing practices are:-

  • Inspection of raw material, in process material and finished products.

  • Hygienic handling of material.

  • Use of good quality ice and water.

  • Maintenance of high standards of personnel hygiene and cleanliness.

  • Better sanitary facilities.

  • Strict adherence to cleaning schedule of utensils, tables, equipments, floor etc.

  • Prevention of entry of insects, rodents and birds into handling and processing areas.

  • Maintenance of correct cold stoeage temperature.

Time, temperature and hygiene play important role in the processing of seafoods. Speedy work, proper icing and cleanliness in processing operations, go a long way in reducing spoilage.


References

Bate Smite, E.C and Bendall, J.R. 1956. Changes in fish muscle after death. British Medical Bulletin 12, pp.2305.

Burt, J.R.1976. Hypoxanthine a biochemical index of fish quality. Process Biochemistry. 11(10).

Gopakumar,K.2000. Enzymes and Enzyme products as Quality Indices. Seafood Enzymes, pp 337-363. Harrd N.F and Simpspn, B.K., (Eds). Marcel Dekker, Inc.New York, Basel, U.S.A.

Karube, I., Marouka, H., Suzuki, S., Watanabe, E and Toyana, K. 1984. J.Agric and Food Chemistry. 32: 314-319.

Lima Dos Santos, C.A.M, James, D and Teutscher, F.1984. Guidelines for chilled fish storage experiments. FAO Fisheries Technical paper, No 210. FAO,Rome.

Putro, S.1986. Better on board handling of oil sardines in the Bali Strait using chilled sea water.Infofish Marketing Digest. 86(1): 33-35.


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