Yet, compared to several other foods containing animal proteins, such as meat and eggs, fish is more prone to spoiling. Fish must be preserved in some way to prevent spoiling. Preservation refers to maintaining the fish, after it has been caught, in a healthy and fit state for human consumption for a short time, such as a few days, or for a longer time, such as many months. The fish is kept as fresh as possible during the preservation time, losing the least amount of flavour, taste, odour, form, nutritional value, weight, and meat digestibility. Its preservation should last from the moment the fish is caught until it is purchased at the counter of the shop.
Fish can be preserved in four ways: freezing, canning, smoking, and pickling. Fresh fish of the highest calibre is necessary for fish preservation. Fish is the meat food that is most prone to microbial deterioration, tissue degradation, and the development of rancidity.
2. Methods of Preservation
Preservation is possible in two ways, both for short and long duration.
2.1. Preservation for short duration
2.1.1. Chilling
The fish is covered in several layers of ice to achieve this. For short-term preservation, such as when transporting caught fish to local markets or canning plants, etc., ice is an excellent option. By lowering the temperature, autolytic enzyme activities are monitored here.
2.2. Preservation for longer duration
The fish are put through cleaning, gutting, conservation, and storage when long-term preservation is necessary.
2.2.1. Cleansing & gutting
The fish that are captured initially are extensively washed in cold, clean water during cleaning to get rid of bacteria, slime, blood, faeces, and other things from their body surface. It is being carried out in a clean environment. The internal organs and viscera of large fish are removed during gutting, and the body cavity is then cleansed.
2.3. Storing & Conservation
To retain the dead fish in fresh condition for a considerable amount of time, conservation is required. Any of the following techniques, including freezing, drying, salting, smoking, and canning, can be used to accomplish this.
2.3.1. Freezing
The removal of heat from the body results in freezing. It is preferable to preserve fish at lower temperatures to prevent putrefaction and to monitor enzymatic, bacterial, and other activity. Fish should be frozen quickly to prevent bacterial growth when it will be kept for a long time. Each component of the product is within the range of 0 to -5 C during fast freezing. Fish that has been properly frozen at -20 C maintains its physical characteristics and nutritional worth for at least a year and is nearly as good as fresh fish. Three factors can cause fast freezing:
a) Fish directly submerged in the cooling medium,
b) Plates-based indirect contact with the refrigerant
c) Forced convection of chilled air applied to surfaces used for heat transmission.
Sharp freezers, air blast freezers, contact plate freezers, immersion freezers, liquid freon freezers, liquid nitrogen freezers, fluidized bed freezers, cryogenic freezers, etc. are all common ways to adapt diverse freezing techniques. The carrier air blast type is the most common type of fast freezing plant installed in India. The air blast freezer is shaped like a tunnel, and the movement of air has a quick impact on heat transfer. Air velocity varies from 30 to 1050 metres per minute, while the temperature employed ranges from 0 to -30°C.
2.3.2. Freeze drying
Via modified deep freezing, all possibilities of denaturation are fully eliminated. The deep-frozen fishse is subsequently dried at -20°C by directly converting ice to water vapour, with any melting resulting in liquid water. The frozen fish is heated to 140°C in a vacuum chamber to accomplish this. The fish is subsequently dried and boxed or canned. The product has a very fresh-looking, flavorful, vibrant, and high-quality appearance.
2.3.3. Salting
In the process of salting, sodium chloride, a common salt, is utilised as a preservative that permeates tissues to stop bacterial development and inactivate enzymes. Purity of salt, quantity of salt used, salting technique, and environmental factors like temperature are some of the elements that affect how salt is used to season fish.
The little fish are not washed before being salted throughout the process. The head and viscera are removed from medium- and large-sized fish, and the fleshy region of the body is chopped longitudinally with the aid of knives. The fish is then rinsed and stuffed with salt to evenly penetrate the flesh. Sharks and other large fish are divided into manageable portions. Typically, sardines, mackerels, seer fishes, cat fishes, sharks and prawns are utilised for salting.
The methods used to salt fish are dry salting and wet salting, which are as follows:-
(a) Dry salting:
In this procedure, the fish is first salted before being packed in layers in cement tanks and tubs. Between the layers of fish, salt is applied at a ratio of 1:3 to 1:8 salt to fish. The ratio of salt to fish varies depending on the type of fish since oily species need more salt. The fish are taken out of the tubs after 10 to 24 hours, cleaned in salt brine, and dried in the sun for two or three days.
(b) Wet salting:
In the previously prepared concentrated salt solution, the cleaned fish are added. Up until it is correctly selected, it is stirred every day. To allow salt to penetrate the flesh of huge fish, longitudinal slits are created in the flesh. The fish's salty water is allowed to drip off after being pickled for 7–10 days. This can be kept for three to four months.
2.3.4. Smoking
The landed fish is cleaned and brined using this technique. Then it is treated with either cold or hot smoke. While cold smoking, a smokeless fire is initially heated to a temperature of 38C. Following this heating, the fish are exposed to cold smoke that has a temperature below 28°C. When smoking something hot, a strong fire first generates a temperature of about 130C. Smoking at a temperature of 40C follows this. The smoke must be thick and moist. Effective controls are required for the following parameters: density, temperature, humidity, circulation speed, pattern, and duration of smoke interaction with fish.
The smoke's phenol concentration adds a distinctive colour and flavour in addition to serving as an antibacterial. Only wood is used to produce smoke and fire.
2.3.5. Canning
In the preservation technique of canning, microorganisms are killed by heat to prevent deterioration. The best kind of fish to can are those that are oily. They include tinned salmon, tuna, sardines, herring, lobster, and shrimp. Since the raw material contains the most harmful strain of Clostridium botulinum, it needs to be thoroughly handled. For it to effectively kill them in big numbers, a temperature of 120°C for 4 minutes or 115°C for 10 minutes is required. Fish that has been cleaned, dressed, and chopped into pieces is then canned in a saline solution. The cans housing the fish and the saline are then double seamed under vacuum. Cans are then sterilised for 90 minutes at 121°C under steam pressure. Following sterilisation, flowing water is used to cool the cans to room temperature.
2.3.6. Drying
In order to prevent bacterial breakdown or enzymatic autolysis, drying entails dehydration or the reduction of fish's moisture content. If the fish are stored in dry conditions and the moisture content drops by up to 10%, they won't go bad. Drying of fish can be done naturally or artificially. In natural drying, fish are washed and dried in the sun after being caught. The dead fish are cleaned, gutted, and have their heads cut off during artificial drying. They are then mechanically washed and dried after being chopped lengthwise to remove a significant portion of their spinal column.
2.4. Value-added fisheries products
One of the most effective strategies to boost profitability in fish processing and sales in both domestic and foreign markets is value addition. Also, it is turning into a demand in the market as wholesalers, retailers, and ultimately customers hunt for fish items that need little to no preparation.
Fish sausages, fish fillets, fish cutlets, dehydrated fish goods, fish pickles, fish flakes/wafers, and fish noodles are a few examples of value-added fish products. Here are some examples:
2.4.1. Fish sausages
Fish sausage is made from ground fish meat mixed with a variety of components (additives) such as salt, sugar, starch, spices, fat, and other substances before being properly wrapped, boiled, and chilled. In other words, fish sausage is a heat-processed, ready-to-eat protein-rich snack.
2.4.1.1. Preparation of fish sausages:
2.4.2. Preparation of fish pickle
One of the safest methods for preserving fish is pickling. In recent years, pickles made from fish have become more popular since they add flavour to dull Asian foods made with starches and are also healthy. Also tasty as an appetiser are fish pickles. Fish pickles currently have a growing domestic and foreign market. It is made by breaking up the edible part of the fish into small pieces, deep-frying them in vegetable oil, and then mixing them with vinegar, salt, and other fried ingredients for flavour development. Before packing, the material is typically held for at least 24 hours to allow for maturation. This is a locally produced item that is currently becoming more well-known.
2.5. Other value-added fishery products
2.5.1. Fish cakes
Fish cakes are frequently made with tuna and mackerel. Fish are cleaned, steam boiled and then layered separately. In addition to salt, pepper, and citric acid, potatoes are cooked. To make fish cakes, the layered fish is combined with the recipe above and vacuum-packed.
2.5.2. Fish salads
The fish are cleaned, and then parts are steam-boiling. To make a fish salad, boiling fish or prawns are combined with tomatoes, salt, garlic, maida, pepper, and oil. This can be kept in storage or utilised right away.
2.5.3. Fish flakes/wafers
Fish used to make flakes or wafers include catfish and thread fin breams. To make flakes or wafers, fish flesh is first boiled and then combined with maida, salt, etc.
3. Conclusion
In this article, we concluded and learnt about types of fish and different preservation techniques. We learnt about the categories of products that can be made from fish, and their preparation processes as well.
4. Reference:
http://ecoursesonline.iasri.res.in/mod/resource/view.php?id=5961
https://vikaspedia.in/agriculture/fisheries/post-harvest-and-marketing/processing-in-fisheries/processing-of-fish#:~:text=The%20traditional%20methods%20of%20processing,in%20developed%20and%20developing%20countries.
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