Seafood Processing: Boat to Fork


Seafood is considered as a valuable source of food that has been used by man from antiquity. Seafood are edible aquatic creatures which are regarded as food for humans. The growth of the seafood market can be attributed to increase in awareness of the health benefits regarding seafood and changing lifestyle of the consumers. Non- vegetarians are slowly changing their lifestyle and shifting towards Pescetarianism. Pescetarianism is the practice of adhering to a diet that only incorporates consumption of fish and shellfish as the only source of meat and excluding land-based meat products like beef, chicken, and pork etc.

Seafood Classification

Seafood are considered as the second to insects in the largeness of population and outnumber all other vertebrates, mammals, birds, reptiles, and amphibians put together. Seafood can be classified into following two types:

1. Fishes: About 250 different species of fishes are used for edible purposes. Edible fishes can be classified based on their fat content as lean (less than 2%fat), medium (2-5% fat) and fat (more than 5% fat).Bombay Duck , halibut, cod, perch and sole are example of lean fish. Fat fish include salmon, sardine, mackerel, tuna etc.

2. Shellfish: They are of two types: molluscs and crustaceans. The former one has soft unsegmented body while the later have segmented bodies. The molluscs are either partially or wholly enclosed in a hard shell that is largely of mineral composition. These include oysters, clams, scallops, and mussels. Crustaceans are covered with crust like shells and they include lobsters, crabs, shrimp, and crayfish. Edible shellfishes are mainly saltwater fishes.

Causes of Fish Spoilage

Fish is a very perishable food material and requires to be cared for, from the moment of catch till cooked for the table or processed in the factory. Spoilage begins as soon as it dies and affects its appearance odor and texture. The causes of deterioration are autolytic / enzymatic and bacterial reactions. These causative factors overlap but in fresh fish, action of spoilage bacteria is the most crucial one. Simultaneously, digestive enzymes of fish also starts to act in a reverse manner immediately after death and initiate processes of biochemical or autolytic degradation. Although the flesh of fish is free from bacteria, the surface slime, gills, and viscera harbor them. While the fish is living, the life processes do not allow these natural microflorae to invade the flesh but soon after the fish is dead, the bacteria start multiplying and, in this process, spoil the fish. From the moment of catch, the fish also get contaminated with terrestrial microorganisms, which also participate in spoilage. Some of these microorganisms could be pathogenic to man and pose problems of public health.

From the moment of catching, the factors that determine the condition of fish reaching the consumer or the site of the processing factory, are:

  • the intervening time, and
  • the temperature of the fish, and
  • hygienic way of handling.

Seafood Processing

The term seafood processing refers to the processes associated with seafood and seafood products between the time they are caught or harvested, and the time the final product is delivered to the customer. Various kinds of methods used for the preservation and processing of fish are as follows:

1.Freezing: Freezing can greatly extend the shelf life and is effective in keeping the fish in  a condition similar to that of fresh fish, if the fish is gutted and frozen down to -29 degree C within two hours of its catch. In some cases, clean whole fish are frozen. Finfish are usually frozen as fillets, steaks, or sticks. Large fish are frozen by the sharp freeze, a comparatively slow freeze. Small fish, fillets and steaks are quick frozen. This type of freezing gives a better produce. The storage life of frozen fish, with a low-fat content can be two years.

2.Drying: The principal methods of drying, or dehydrating, fish are by forced-air dryingvacuum drying, or vacuum freeze-drying. Each of these methods involves adding heat to aid in the removal of water from the fish product. During initial stages of drying, known as the constant-rate period, water is evaporated from the surface of the product and the temperature of the product remains constant. In the final stages of drying, termed as the falling-rate period, the temperature of the product increases, causing water to move from the interior to the surface for evaporation.

3.Curing: Curing reduces water activity, by addition of chemicals, such as salt, sugars, or acids. There are two main types of curing used in the fish industry: dry salting and pickle-curing. In dry salting type, the butchered fish is split along the backbone and buried in salt (called a wet stack). Brine is drained off until the water content of the flesh is reduced to approximately 50 percent (the typical water content of fresh fish is 75 to 80 percent) and the salt content approaches 25 percent. In heavy or hard-cure salting, an additional step is taken in which warm air is forced over the surface of the fish until the water content is reduced to about 20 percent and the salt content is increased to approximately 30 percent. Most dry-salted fish products are consumed in warm, humid countries or in areas that have few means of holding products in refrigeration or cold storage.

4.Canning: Fishes with high fat content are considered as most suitable food material for canning. Fishes like salmon, tuna etc. are canned in additional fish or vegetable oil, whereas shrimps are canned in brine. Canning retains the natural flavors of the fish. Generally, canning is performed for the export variety of fishes. Shellfish becomes dark or discolored during canned storage. This is due to the release of Hydrogen sulfide from the sulfur components of the fish, which reacts with the iron in the can to give black iron sulfide. This can be avoided using enamel containing zinc.

Fish products have attracted considerable attention as a source of high amounts of important nutritional components like high-quality protein, essential vitamins, minerals, and healthful polyunsaturated fatty acids to the human diet. As a result of this the fresh fish and seafood’s rank third among the food categories. Consumption of both freshwater and seawater fish is expected to increase in the future. As fish is highly nutritious, it is also highly susceptible to spoilage, due to intrinsic and extrinsic factors. Therefore, Proper processing and packaging will help in maintaining the eating quality of fish for extended period.

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