Report on Quality Assessment of Smoke Cured and Sun Dried Koral, Shol, Kajuli and Tapsya in Laboratory Condition

Report on Quality Assessment of Smoke Cured and Sun Dried Koral (Lates calcarifer), Shol (Channa striatus), Kajuli (Ailia coila) and Tapsya (Polynemus paradiseus) in Laboratory Condition

Bangladesh is a South Asian country located in between latitude 20o-34o and 26o-39o north and longitude 80o 00´ and 92o 41´ east. The country is criss-crossed with hundreds of rivers. The climate of Bangladesh is unique for aquaculture and fisheries resource management. The Bay of Bengal is situated at the south of the country. Winter lasts only for about 2 months in the country. Temperature and rainfall ranges from 07oC to 40oC and 1170 to 3400 mm respectively.
Fish as a food is one of the most familiar, popular, tasty and nutritionally enriched item of food around the world including Bangladesh. As a result of joining and accepting the policy of global market economy along with so many food items, garments, pharmaceutical products, so on and so forth fish and fishery products also get the opportunity to enter in the global market.

In Bangladesh, fisheries sector plays a vital role in our national economy regarding employment generation, animal protein supply, foreign currency earning and poverty alleviation. According to the report of BBS, 2006, fisheries sector is contributing 65.71% of the total export earning and 4.86% to the GDP. About 12 million people are directly and indirectly involved in this sector. Labour employment in this sector is increasing approximately 3.5% annually. Fish production is also increasing day by day through application of modern culture technology.

Fish production was increased to 24.40 lakh metric tons in 2006-2007, which was 23.28 lakh metric tons in 2005-2006 (DoF, 2008). Fish production in some flood plains increased from 150 kg/ha to 2000-3000 kg/ha in recent years. The processed fish products are exported to the European countries, U.S.A and Japan. About 95% of total fish products are exported to those countries. Remaining portion is exported in Southeast Asia and Middle East.

Dry and dehydrated fish is one of the important export items in Bangladesh. The demand for dried and dehydrated fish as an export item is increasing day by day. According to the Fishery statistical year book in 2005-2006, the quantity of exported dry fish and fish product from Bangladesh was 150 tons and which valued 2.19 crore taka and in 2006-2007, it was 77 tons and valued 1.34 crore taka. On the other hand, in 2005-2006 the quantity of exported salted and dehydrated fish was 519 tons and valued 19.84 crore taka and in 2006-2007, it was 441 tons and valued 12.80 crore taka (DoF, 2008). It is indicating that the demand of salted and dehydrated fish product is increasing day by day than simple dried fish.

Fish is the primary source of animal protein in the diet of the most people of Bangladesh. Fresh and dried fish is a very popular food item. Fish contributes about 9% of the total protein consumption and 63% of the per capita animal protein intake in the daily diet of the people. Fish protein is said to be healthier and cholesterol free. Fish protein that contains all of the Essential Amino Acids (EAA) in right proportion and is called complete protein needed for the proper growth and development of human body (Hossain, 1996).

Fish tissue is characteristic in being rich in protein and non-protein - nitrogen (e.g. amino acids, trimethylamine-oxide (TMAO), creatinine), but low in carbohydrate resulting in a high post mortem pH (<6.0). Further, the pelagic, fatty fishes have a high content of lipids consisting mainly of triglycerides with long-chain fatty acids, which are highly unsaturated. Also the phospholipids are highly unsaturated and these circumstances have important consequences for spoilage processes under aerobic storage conditions.

The purpose of processing and preserving fish is to get fish to an ultimate consumer in good, usable condition. The steps necessary to accomplish this begin before the fishing voyage starts, and do not end until the fish is eaten or processed into oil, meal, or a feed. Fish begins to spoil as soon as it is caught, perhaps even before it is taken out of the water. Therefore, the key to delivering a high quality product is needed a close attention to small details throughout the entire process of preparation, catching, landing, handling, storage, and transport (Richard, 1986).

Fish that becomes spoiled or putrid is obviously unusable. Fish that is poorly cared for may not be so obviously bad, but it loses value because of off-flavors, mushy texture, or bad color that discourages a potential purchaser from buying. If customers have bought one bad fish, they probably won't buy another. On the other hand, if any one consistently delivers good quality at a fair price, people will become loyal customers.
Spoilage proceeds as a series of complex enzymatic bacterial and chemical changes that begin when the fish is netted or hooked. This process begins as soon as the fish dies. The rate of spoilage is accelerated in warm climates. The fish's gut is a rich source of enzymes that allow the living fish to digest its food. Once the fish is dead, these enzymes begin digesting the stomach itself. Eventually the enzymes migrate into the fish flesh and digest it too. This is why the fish becomes soft and the smell of the fish becomes more noticeable.

There are countless bacteria naturally present on the skin of the fish, in the gills, and in the intestines. Normally, these bacteria are not harmful to a living fish. Shortly after death, however, they begin to multiply, and after two to four days they ingest the flesh of even a well-iced fish as enzymatic digestion begins to soften it. The bacterial load carried by a fish depends on its health, its environment, and on the way it was caught.
Both enzymatic digestion and bacterial decomposition involve chemical changes that cause the familiar odors of spoilage. Oxygen also reacts chemically with oil to cause rancid odors and taste. The aim of fish processing and preservation is to slow down or prevent this enzymatic, bacterial, and chemical deterioration, and to maintain the fish flesh in a condition as near as possible to that of fresh fish (Richard, 1986).

One thing is very much clear that proper care and preservation methods are to be applied if anybody or company or traders wants to carry the freshly harvested various species of fishes (freshwater or of marine origin) to the saling centers in and around of the fish catching centers including even to remote areas of Bangladesh. One of the most common and familiar preservation method is applied for carrying the fresh catches of fishes including lean fishes, fatty fishes etc. to the marketing sites is icing preservation of fish, which actually help to keep the fishes with minimum rate of spoilage thereby increasing the shelf-life of the fish up to a period longer than without application of any preservation methods.

Though icing preservation of fish get a priority for preservation of fish not only during transportation but also during its marketing operation. But it has been observed to have a small defect. The defect is that icing preservation of fish is a short term preservation method. That means, by application of this type of preservation method, we are not able to preserve the fishes for a long period if we want to get a longer shelf life.

In contrast to the short term preservation of fish and fish products, there are some long term preservation and processing methods. Application of which extends the shelf life of those processed fish and fish products even up to several years. These methods are discussed below:

The least expensive method of preserving food is drying. It is also the oldest. Dried foods use less storage space than other ways of preserving food. There are several methods of drying; each has advantages and disadvantages:
Sun drying of fish depends on the temperature and the relative humidity of the weather at that period. Sun drying can be used when the temperature is in the region with low humidity and low air pollution. A major advantage of sun drying is low cost. Drying trays with nets are used to protect against bugs. Another possible advantage is the sun's sterilizing effect caused by ultraviolet rays that may slow the growth of some organisms. The disadvantage is that sun drying can only be done when the temperature is high and the humidity is low (Hillers, 2001).

Solar drying is like sun drying, only better. The sun's rays are collected in a solar box; drying temperature is higher and drying time is shortened.

Air drying reduces the moisture content of fish to the point where bacterial action ceases. Fish preserved by air drying tends to be tough and stringy. Most people will not eat fish preserved this way unless they must. If the weather is dry, fish may be air dried. Take care to keep the fish in shade, exposed to breeze. Keep flies and insects away.

Kiln or tunnel drying of fish is a more complex process, and the final product is much more palatable than natural air dried fish. It requires careful control of many variables, such as relative humidity, air temperature and velocity, and rate of drying.

Oven drying is to dry small amounts at one time, the oven drying method can be used. There is little or no investment in equipment. You don't have to depend on the weather. Most foods can be dried in an oven (Hillers, 2001).

In dehydrator drying, dehydrators yield a better-quality dried product than any other method of drying. A dehydrator should have a heat source, a thermostat, and some method of air circulation (Hillers, 2001).

Salting and pickling, along with various kinds of drying, are the traditional methods for preserving fish. Sodium chloride (NaCl), also called salt, common salt, and table salt, is generally recognized as a safe antimicrobial and incidental food additive (Klaassen, 1986). Salt has been used for centuries as a seasoning and flavor enhancer as well as a preservative or curing agent. Egyptians preserved food by salting or sun-drying. Salting as a method of preserving fish has been used for centuries and in many places around the world such as Asia, Europe, and Latin America. The simplicity of the salting process, the low cost of production and the ease with which it combines with other preservation methods, such as drying or smoking, has led to its popularity and extensive use (Berhimpon et al., 1991).

Freeze drying involves the use of a vacuum to draw water out of the fish. Irradiation can be used to kill the microorganisms in the fish; however, this technology is still experimental. Another method of preserving fish, pouch technology, is advanced
but may be usable in some locations (Richard, 1986).

Canning is very effective method though costly. Production is very good and retains much of flavour.

Smoking is a method of fish preservation affected by a combination of drying and deposition of naturally produced chemicals resulting from the thermal break down of wood (Rawson, 1966). It is a popular technique of fish preservation in many parts of the world. Modern fish smoking is, however, used to impart colour and flavour to the product rather than a simple preservation. Smoked fish is a delicacy in modern world. Its importance in many countries of Central Africa and Middle-eastern Asia is, on the other hand, largely a technical necessity rather than delicacy due to dry and less humid climatic conditions and other reasons (Watanabe and Dzekedzeke, 1969). In Southeast Asia, smoking is practiced not necessarily to impart desirable colour and flavour, but mainly to accelerate the drying of fish (Clucas and Ward, 1996).

The advantages of smoking fish are manifold. Fish smoking prolongs shelf life, enhances flavour and increases utilization in soups and sauces. It reduces waste at times of bumper catches and permits storage for the lean season. It increases protein availability to people throughout the year and makes fish easier to pack, transport and market.
Sun drying is one of the most important low cost methods of fish preservation and the product plays an important role particularly providing nutrients to the all category of people throughout the world including Bangladesh. About 20% of the artisanal catch is sun dried and consumed in the internal domestic market (Coulter and Disney, 1987).

In Bangladesh, a lot of works were carried out on drying (Ahmed, 1979; Morshed, 2005), salting (Begum, 2004; Akter, 2006) and freezing (Rabbane, 2006) but few scientific works on smoke curing. On the other hand, smoke curing method is a method which is not affected by climatic condition as well as the smoke cured products has a special taste and odour. It also has world wide acceptability as processed fish food.

The experimental fishes such as Koral, Shol, Kajuli and Tapsya fishes are very delicious and nutritionally enriched. The nutrient content of processed fish is very much higher than raw fish.

Due to high palatable, taste and rich in nutrients four commercially important variety of Bangladeshi fishes such as Lates calcarifer (Bloch, 1790), Channa striatus (Bloch, 1801), Ailia coila (Hamilton, 1822) and Polynemus paradiseus (Linnaeus, 1758) have been selected for the present thesis study.

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