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Local production of refrigeration equipment and machinery for the fish industry.

Sea fish or marine fisheries form valuable natural resources of any country. Pakistan has a coastline of about 1050 kilometers and is very rich in fisheries and whose potential is yet to be determined.

In 1990-91, the total fish production was estimated at 455,000 tonnes against 446,000 tomes in 1989-90 and 445,000 tonnes in 1988-89. The following figures of exports illustrate the point:
Year Million $

1988-89 110
1989-90 95
1990-91 114
1991-92 103
1992-93 165

Fish is perishable among the food which, begins to spoil immediately after death. Since the rate of spoilage depends on the temperature of fish, the spoilage of fish can be reduced if the temperature can be brought down rapidly. The refrigeration plays an important role in fish preservation although there are other methods such as drying, dehydration, curing, irradiation and canning.

The Fisheries Industry in Pakistan has developed as one of the major sources of foreign exchange earner. The most significant is shrimp trawled mostly near Pakistan's coastal water. The frozen shrimp forms major part of export (80 per cent of the total) with 5 per cent canned shrimp.

Chilling of Fish

Preservation of fish by refrigeration comes under the category of two groups:

a) Chilling and b) Freezing

Chilling: The chilling of fish at a temperature of 0 |degrees~ C, that is just above the freezing point of fish, does not spoil completely but checks for some time. There are two methods of chilling, one is chilling with ice and the other is chilling with sea water known as refrigerated sea water (RSW).

Chilling with ice generally practiced in most of the fishing industry. But RSW has not been practiced widely in the fishing industry, though it maintains uniform temperature, causing less damage to fish during heavy catch and larger loading capacity. It has been observed that some bigger imported trawlers have RSW storage facilities which make the better.

Fish Freezing: There are several methods for the freezing of fish such as sharp freezing, plate freezing, air blast freezing by immersion or spray and ultra rapid freezing etc.

Plate Freezing

There are two types of plate freezing namely:

a) Horizontal plate freezing and b) Vertical plate freezing.

In the first case, freezing is accomplished by refrigerant flowing through connected passage. In the earlier plate freezers on one side of the plates was made to come in contact with the product.

While the vertical plate freezer has been developed for freezing whole fish on board fishing vessels which has not been practiced widely in Pakistan as we are not having larger size of vessels.

Freezing by Immersion

Fish is frozen by using a cold liquid or by spraying. In advance countries this method has been used where big trawlers are employed and where RSW and cold storage facilities are available.

Heat transfer can be rapid even with moderate circulation. In this method heat transfer can be rapid even with moderate circulation because there is good contact with the product. Thus, like air blast freezer, the immersion freezer will accommodate fish of various sizes and shapes but will be more compact and consume less power. In the direct method, the product is immersed or sprayed with a sodium chloride brine. In the indirect method, the product is contained in moulds which makes possible the use of other cooling media such as calcium chloride brine.

Sodium chloride brine can be made up to any desired strength according to the desired freezing point of the brine. A saturate solution which contains about 26 per cent salt, freezes at 21 |degrees~ C. In practice, therefore, the operating temperature cannot be lower than about 19 |degrees~ C. This is a serious limitation because the refrigerant temperature should be below 30 |degrees~ C and storage temperature should be 23 |degrees~ C or lower in most applications. This method of freezing has not so far become popular in our country owing to the lack of such facilities in our fishing vessels.

Individual Quick Freezing

An important variation of the freezing technique is the individual quick freezing (I.Q.F.). This method is gaining popularity in the shrimp industry as compared to block frozen shrimps. According to I.Q.F. process the shrimps are passed on a conveyor belt through a trough of cold water. As against block freezing the quality of ice required is much less and the shrimps acquire a glaze. I.Q.F. shrimps can be packed either in waxed cartons or in polyethylene bags. This offers a great advantage for retail packing in small sizes.

Accelerated Freeze Drying

Accelerated Freeze Drying (A.F.D.)is the newest approach to the food preservation and the novel processing method is fast developing into a multi-million dollar industry in the U.S.A. In this process the removal of water from frozen food is effected by sublimation. The final product is a dried food and can be stored for a long period without any refrigeration. To reconstitute these dried foods into a ready-to-eat state only water has to be added. Freeze dried shrimps and crabs are becoming increasingly popular with restaurants, hospitals, schools and other away from home eating places. Large quantities of freeze dried foods are purchased by the Armed Forces as combat ration items.

Shrimp was one of the first freeze dried foods that entered the institutional market and has since grown in popularity. Recently the quality of several freeze dried sea-foods was compared with frozen foods and palatability tests were carried out. Plain shrimps, shrimps prepared into a salad, shrimp made into a creamed dish and shrimp creole prepared as a mix in a processing plant were subjected to taste comparison. Encouraging results have been claimed and no adverse comments were made by the panelists. A wide market for freeze dried shrimps is anticipated.

Ultra-Rapid Freezing

Freezing is accomplished by direct contact with liquefied gases which evaporate at very low temperatures at atmospheric pressure. The most notable of these liquid gases are liquid nitrogen and liquid carbon dioxide. Liquid nitrogen has been used in refrigerated transport vehicles and in freezers for producing individual quick frozen (IQF) shrimp in many of the developed countries. In freezing, the rate of evaporation of nitrogen at 196|degrees~C will not be less than 1 kg. per kg. of fish. In addition, there may be the requirement for the cold store and other losses. Hence it is clear that unless we are able to get liquid nitrogen at comparatively cheaper price, the method may not be economical, as things stand today in Pakistan. However, research on development of freezers with liquid nitrogen is in progress at Central Institute of Fisheries Technology, Cochin, and elsewhere. For liquid carbon dioxide also, cost is the main criterion. In developed countries, solid carbon dioxide (dry ice)is being used for refrigerated trucks.

Even though our export of prawns is progressing year by year, the latest trend in the export market is for IQF shrimp whereas our main export is in the form of blocks. IQF machineries have been developed in many developed countries using either liquid nitrogen or using fluidised bed system. In the latter system, the IQF products are produced by feeding shrimp into a perforated conveyor through which cold air passes from the bottom up in such a way that the product is travelling in a fluidised manner. Freezing by this method is accomplished in a few minutes. It is high time for us to develop this type of machineries to compete in the export market.

Product Diversification

The Pakistani industry has been advised to diversify production to initiate the manufacture of breaded shrimps, etc, and to exploit Pakistani's tuna fish resources. 'Convenience foods' are gaining great popularity in the USA and other advance countries. Product diversification would, therefore, be highly desirable from the export stand-point.

Breaded Shrimps

A large proportion of shrimps exported from Pakistan are ultimately converted into breaded shrimp in American food processing factories. The shrimps are cut on a pranto machine and removal of the shell and veins is done by hand. Breading is carried out by machine and the viscosity of the dough is electronically controlled. There is a great demand for breaded shrimps in the USA. The American housewife prefers a food packet which is tasty, attractive and can be consumed just by warming in an oven.

Many other convenient foods like stuffed, fried and cocktail shrimps, etc. are becoming popular and diversification along these lines has been suggested.

The need for adequate cold storage facilities to conserve the abundant seasonal catch and need for developing the fish processing industry can hardly be overemphasized. The application of modern scientific research and the introduction of improved methods of catching, storing and packaging combined with strict quality control during all the stages will benefit the industry to a great extent and will bring a greater foreign exchange.
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Author:Nazri, M.M.
Publication:Economic Review
Date:Sep 1, 1993
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