CHAPTER TWO: SOME ASPECTS OF FISH PRESERVATION AND PROCESSING TECHNIQUES
Ibrahim, Baba Usman
2.1 Fish Preservation
Fish preservation is the method of extending the shelf life of fish and other fishery products. Preservation method maintains the quality of fish for a longer period of time. A well processed fish will store for a long period.
2.2 Fish Processing
When fish are caught or harvested for commercial purpose, they need some processing, so that they can be delivered to the consumers, or next part of marketing chain in a fresh and undamaged condition.
2.3 Preservation Techniques
Many different techniques have been used to preserve fish quality and to increase their shelf life. They are designed to inhibit or reduce the metabolic changes that lead to fish spoilage, by controlling specific parameters of fish and, or that of its environment. The techniques are classified as follows:-
(a) Techniques based on temperature control:-
This involves the use of different types of technologies to decrease the fish temperature to levels, where metabolic activities, catalyzed by autolysis or microbial enzymes are reduced or completely stopped. This is possible by refrigeration or freezing, where the fish temperature is reduced, respectively to approximately 00C for refrigeration, -00C for Freezing and -1560C for Cryo - Preservation.
(b) Techniques based on the control of water activity:-
Water activity (aw) is a parameter that measure the availability of water in fish flash. It is express as a ratio of water vapour pressure in fish / vapour pressure of pure water at the same temperature and pressure. Water activity (aw) varies from 0-1. Water is necessary for microbial and enzymatic reactions, and several preservation techniques have been developed to tie up this water and thus reduce the water activity (aw). These include drying, salting, smoking, freezing, freeze-drying, the use of water binding humectants and combination of
these techniques. Some of these techniques have been in use for thousands of years and can be implemented very simple e.g. salting.
(c) Techniques based on the control of oxydo-reduction (Redox) potential:-
Some spoilage bacteria and lipid oxidation require oxygen. Therefore, reducing the oxygen around the fish will increase its shelf life. This is possible by vacuum packaging, or by controlling or by modifying the atmosphere around the fish. Specific combination of C02, 02 and N2 characterized control (CA) or modified atmosphere (MA), vacuum package (CA) storages are often combine with refrigeration for fish preservation.
(d) Techniques based on the physical control of microbial fish loads, its chemical and enzymatic activity:-
The physical method, use heat (cooking, blanching, pasteurizing, sterilizing), ionizing irradiation (for pasteurization and sterilization) or micro wave heating. Cooking or pasteurizing are processes that do not allow complete inactivation of microorganisms and thus often require to be combined with refrigeration to preserve fish products and increase, their shelf life. This is not the case with sterilized products, which are stable at ambient temperature (<400c). These require packaging in metal cans or retort able pouches before the heat treatment “canning”.
(e) Combination of several preservation techniques:-
Two or more of the already described, techniques can be combined to improve preservation efficiency, while reducing undesirable effects such as the denaturation of nutrient by severeheat treatment. Combinations already in use include pasteurisation – refrigeration characterized control (CA) or modified Atmosphere (MA) – refrigeration, salting – drying, salting – smoking and salting – marinating.
2.4 Fish Preservation and Fish Processing Methods
There are different methods used to preserve and processing fish. The methods include:-
ü Freezing method
ü Salting method
ü Smoking method
ü Drying method
ü Curing method
ü Dehydration method
ü Pickling method
ü Cooking method
ü Canning method
ü Fermentation method
2.4.1 Fish Preservation Methods
(a) Salting method
Salting is a traditional method of preserving fish in many countries of the world. It is often used in combination with drying and smoking. Drying the fish removes water and lowers the water activities (water available for the support of microbial growth which causes spoilage).Some water is removed from the fish during salting.
Salting also lowers the moisture or water content of fish and other fishery products to a point where micro - organisms cannot live and grow. Salt partially dehydrates the fish and kills the bacteria. Salt (Nacl) also improves the fish texture because it firms up the fish.
2.4.2 Basic methods of applying salt to preserve fish
Salt is applied by the following basic methods: -
(a) kench salting in which granular salt is rubbed into the surface of the split fish, the fish are stacked with sprinkling of salt between each layer and the liquid (pickle) which form is allow to drain away.
(b) Pickle salting: - cover the fish with salt and pack them in layers in water tight containers. This forms the pickle that serves as the saturated brine solution that covers the fish completely.
(c) Brine salting: - immerse the fish in a saturated solution made up of twenty five (25) parts of salts and hundred (100) parts of water. Brine salting is done only as a temporary way to preserve fish before they are dried, smoked or processed.
(d) Dry salting: - involve running granular salt on the fish. The proportion of salt to fish varies from ten percent (10%) to thirty five (35%) of the fish weight.
Steps in salting method
(i) Place the fish either in crushed ice or frozen brine.
(ii) Remove the fins.
(iii) Remove the head (optional).
(iv) Split the fish along the dorsal section spread it open.
(v) Take out the black membrane of the fish.
(vi) Wash the fish thoroughly and drain it a little.
(vii) Rub the fish with salt.
(viii) Arrange the fish in a container; place the container inside a refrigerator.
(b) Salting - Smoking method
This method combines with salting, precooking and drying. The final process is smoking which dehydrates the fish further. The smokes give colour and flavour to the fish.
Steps in salting - smoking method
(i) Clean the fish by removing the gill and make half inch (1/2) slit in the belly. Wash the fish thoroughly with clean water.
(ii) Soak the fish in brine solution (one part of salt to ten part of water), for twenty (20) or more minutes, depending on the size of the fish.
(iii) Place the fish in the immersion basket made up of woven bamboo strips or wire netting. The basket will be suspended during the immersion in boiling brine. Cooked for two (2) to four (4) minutes, or more, depending on the size of the fish.
(iv) Drain the fish, allow them to cool after being cooked in brine solution place it in a layer of wire screen (rattan or bamboo) and have it dried in a cool and shady place.
(v) Smoke the fish in tin cans for one (1) to two (2) hours until, it gets golden brown. The length of smoking actually differs, depending on the size of the fish. And the smoke produced.
(vi) Packed the smoked fish in coarsely woven cane / bamboo basket. Line the size newspapers. Cool the fish completely before packing them to allow moisture to escape and prevent the attack of mould and bacteria.
(C) Drying method:-
This method is also known as natural dehydration. Like the salting method, it lowers the water content of the fish to a point where microorganisms, bacteria, enzymes and yeast cannot grow and multiply. The most popular fish preservation method is solar dehydration. It is done in combination with salting. Fish dried under the sun look and taste better. The method of drying involves the removal of the water content of the fish until such time, that the fish moisture is completely extracted. This method prevent the possible growth of the microorganisms, that causes food spoilage. It can be done using the heat of the sun, and it is called solar drying. In the dehydration, an artificially heating, air is used in the dehydration of the fish. This heated air comes from the mechanical driers.
Steps in drying method
The followings are the steps involved in the drying method of fish preservation:-
(i) wash the fish thoroughly
(ii) soak the fish in ten percent (10%) brine solution for half (1/2) hour to draw out the blood.
(iii) Squeeze or open the belly cavity, remove the visceral or internal organs.
(iv) Soak the fish for three (3) to six (6) minute in a concentrated brine solution to partially draw out the moisture or water content of the fish.
(v) Place the salted fish in drying trays and dry it under the sun.
(vi) When the fish are thoroughly dried, pack them and store them in a clean, dry place.
(D) Curing method
This method uses chemical preservatives (including vinegar and salt), smoke and other physical factors, to reduce the moisture or water content of the fish cured, fish or fishery products possess flavour and texture completely different from those of the fresh fish.
(E) Dehydration / Drying method
Dehydration is an artificial process of drying because it is done with the used of mechanical devices such as an oven, that produces artificial heat for drying.
(F) Pickling method
Pickling is a method of preserving fish in brine or vinegar. It can be done with or without bacterial fermentation; the method of pickling involves using vinegar as well as other spices and ingredients as preservatives. The acetic acid of the vinegar presents bacterial and other microorganisms from growing, which result in the preservation of the fish. This method improves the fish’s taste.
(G) Fermentation method
Fermentation is a fish preservation method in which fish in brines solution, undergo chemical reaction. Fermentation is a process in which the musculature in the fish is broken through the enzymatic reaction. In this method, the flesh of the fish to be preserved, is allow to get “ripe”. And with this, the flesh will start to disintegrate, until such time that the flesh will undergo “aging”. Fermentation could take up to eight months in the normal process. However, this only took place in less than a month, when pure salt was used, and the temperature in the process increase from 370C to about 450C.
Steps in fermentation method
(i) clean the fresh fish well, remove scales, shells, seaweeds and other material.
(ii) Wash the fish in a weak brine solution (1 part of salt to 9 parts of water drain it well, cover the container water draining the al among to keep flies
(iii) Mix fish thoroughly with salt (1 part to 3 parts of alamang)
(iv) Place the fish-salt mixture in a clean container.
(v) Stored the preserved fish in a clean and warm place.
(H) Freezing method
This is a method of keeping fish in a condition close to that of a fresh fish using ice or chilling systems for a few week or for a longer period, depending on the need and situation of preservation. There are circumstances however, when fish need to be kept for long period, to enable fish to be distributed and sold in distant markets, and to stock pile products for lean season. If fish are properly frozen and stored at correct temperature, it is possible to provide a product which closely resembles fresh fish, in many cases, the consumer will be unable to distinguish between pieces of frozen fish and fresh fish. Fresh fish contains approximately eighty percent (80%) water. At normal atmospheric pressure, pure water will change from liquid to solid (ice) at 00c i.e. it will freeze. However, the water in fish fluid contains dissolve salts and chemicals which have the effect of lowering the temperature at which the water begins to freeze. The exact temperature of freezing varies between species and size of fish, but is usually between -10c and -20c. As the temperature drop below this critical temperature water tend to be frozen out of solution.
Steps to preserving fish by freezing
(i) Remove all the guts and clean the fish as soon as possible after catching.
(ii) Cut large fish into strips, and freeze small fish whole.
(iii) To preserve fish, first wrap them in a manner (polythene bag) that is air tight, and to prevent freezer burn. This will also aid in reducing the changers of unwanted flavours that are not natural to the fish.
(iv) Make sure the freezer temperature is at or below zero degree °C. This will ensure that the preserving process is not disturbed by a lapse in temperature.
(v) Date the fish as its been froze, so as to know when they will no longer be safe to eat.
(I) Cooking method
Cooking is a way to prevent wastage or spoilage of fish. Cooking fish with vinegar prolonged the period of preservation.
2.4.3 Fish Processing Methods
(A) Canning method:-
Canning is the packing of fish in airtight containers such as tin, cans and glass, jar which prevent air and micro organisms from entering. Through the heat processing, microbial inside the can are destroyed, thus preventing spoilage under normal condition and allowing the fish to be stored for longer periods. Sardines and salmon are the most commonly canned fish in the market.
Steps in canning method
The followings are steps involved in the canning method of fish preservation:-
(i) Remove the scales of the fish.
(ii) Remove the internal organs, the head and the tail of the fish.
(iii) Cut the cleaned fish to fit the size of the can to be used. For thirty minutes (30Mins) soak the fish in twenty percent (20%) brine solution.
(iv) Half – fry the fish in oil.
(v) Fill each can with half – fried fish leave about ¼ inch space. Add a table spoon of corn oil and tomato sauce. Do not add salt because the fish has been brined.
(vi) Sealed the filleted cans temporarily. Use the first roll operation of the can sealer.
(vii) For ten minutes (10mins), stem the clinches cans without pressure to exhaust the air inside the cans. Then, seal the can, using the can sealer.
(viii) For forty five minutes (45minuts), process sealed cans at 15 Ib pressure, using the can sealer.
(ix) Immediately, cool the pressed can in running water.
References
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