Fish preservation is the method of increasing theshelf life offish and otherfish products by applying the principles of differentbranches of science in order to keep the fish, after it has landed, in a condition wholesome and fit for human consumption.[1][2] Ancient methods of preserving fish includeddrying,salting,pickling andsmoking. All of these techniques are still used today but the more modern techniques offreezing andcanning have taken on a large importance.
Fish curing includes and of curingfish bydrying,salting,smoking, andpickling, or bycombinations of these processes have been employed since ancient times. On sailing vessels fish were usually salted down immediately to prevent spoilage; the swifter boats of today commonly bring in unsalted fish. Modernfreezing andcanning methods have largely supplanted older methods ofpreservation. Fish to be cured are usually first cleaned, scaled, and eviscerated. Fish are salted by packing them between layers ofsalt or byimmersion inbrine. The fish most extensively salted arecod,herring,mackerel, andhaddock. Smoking preserves fish by drying, bydeposition of creosote ingredients, and, when the fish are near the source of heat, by heat penetration. Herring and haddock (finnan haddie) are commonlysmoked.Kippers are split herring, andbloaters are whole herring, salted and smoked.Sardines,pilchards, andanchovies are small fish of the herring family, often salted and smoked and then preserved inoil. Fish are dried under controlled conditions oftemperature,humidity, andair velocity. Since the dried product is relatively unappetizing and rehydrating slow, other preservation methods are common.
Preservation of marine products is of great importance to the coastal poor. Preserved fish products ensure adequate protein during low fishing periods. Subsistence fishers use their abundant catch of small fish to make fermentedfish paste andsmoked fish with the assistance of family members. Large fish are used to make fermented fish or salt dried fish. Other important processing activities include drying of small shrimp, squid, ray and shark and preparation ofshrimp paste.[3]
In the past, fishing vessels were restricted in range by the simple consideration that the catch must be returned to port before it spoils and becomes worthless. The development ofrefrigeration and freezing technologies transformed thecommercial fishing industry: fishing vessels could be larger, spending more time away from port and therefore accessing fish stocks at a much greater distance. Refrigeration and freezing also allow the catch to be distributed to markets further inland, reaching customers who previously would have had access only to dried or salted sea fish.
Canning, developed during the 19th century, has also had a significant impact on fishing by allowing seasonal catches of fish that are possibly far from large centres of population to be exploited. For example:canned sardines.
Preservation techniques are needed to prevent fishspoilage and lengthenshelf life. They are designed to inhibit the activity of spoilagebacteria and themetabolic changes that result in the loss of fish quality.Spoilage bacteria are the specific bacteria that produce the unpleasant odours and flavours associated with spoiled fish. Fish normally host many bacteria that are not spoilage bacteria, and most of the bacteria present on spoiled fish played no role in the spoilage.[4] To flourish, bacteria need the right temperature, sufficient water and oxygen, and surroundings that are not too acidic. Preservation techniques work by interrupting one or more of these needs. Preservation techniques can be classified as follows.[5]
If the temperature is decreased, the metabolic activity in the fish frommicrobial orautolytic processes can be reduced or stopped. This is achieved byrefrigeration where the temperature is dropped to about 0 °C, orfreezing where the temperature is dropped below -18 °C. On fishing vessels, the fish are refrigerated mechanically by circulating cold air or by packing the fish in boxes with ice.Forage fish, which are often caught in large numbers, are usually chilled with refrigerated or chilled seawater. Once chilled or frozen, the fish need further cooling to maintain the low temperature. There are key issues with fish cold store design and management, such as how large and energy efficient they are, and the way they are insulated andpalletized.[5]
An effective method of preserving the freshness of fish is to chill with ice by distributing ice uniformly around the fish. It is a safe cooling method that keeps the fish moist and in an easily stored form suitable for transport. It has become widely used since the development of mechanicalrefrigeration, which makes ice easy and cheap to produce. Ice is produced in various shapes; crushed ice and ice flakes, plates, tubes and blocks are commonly used to cool fish.[6] Particularly effective isslurry ice, made from microcrystals of ice formed and suspended within a solution of water and afreezing point depressant, such as common salt.[7]
A more recent development ispumpable ice technology. Pumpable ice flows like water, and because it ishomogeneous, it cools fish faster than freshwater solid ice methods and eliminates freeze burns. It complies withHACCP andISO food safety and public health standards, and uses less energy than conventional freshwater solid ice technologies.[8][9]
Thewater activity, aw, in a fish is defined as the ratio of thewater vapour pressure in the flesh of the fish to the vapour pressure of pure water at the same temperature and pressure. It ranges between 0 and 1, and is a parameter that measures how available the water is in the flesh of the fish. Available water is necessary for the microbial and enzymatic reactions involved in spoilage. There are a number of techniques that have been or are used to tie up the available water or remove it by reducing the aw. Traditionally, techniques such asdrying,salting andsmoking have been used, and have been used for thousands of years. These techniques can be very simple, for example, by using solar drying. In more recent times,freeze-drying, water-bindinghumectants, and fully automated equipment with temperature and humidity control have been added. Often a combination of these techniques is used.[5]
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Heat or ionizing irradiation can be used to kill thebacteria that cause decomposition. Heat is applied by cooking, blanching or microwave heating in a manner that pasteurizes or sterilizes fish products. Cooking or pasteurizing does not completely inactivate microorganisms and may need to be followed with refrigeration to preserve fish products and increase their shelf life. Sterilised products are stable at ambient temperatures up to 40 °C, but to ensure they remain sterilized they need packaging inmetal cans orretortable pouches before the heat treatment.[5]
Microbial growth and proliferation can be inhibited by a technique calledbiopreservation.[10] Biopreservation is achieved by addingantimicrobials or by increasing theacidity of the fish muscle. Most bacteria stop multiplying when thepH is less than 4.5. Acidity is increased byfermentation,marination or by directly adding acids (acetic, citric, lactic) to fish products.Lactic acid bacteria produce the antimicrobialnisin which further enhances preservation. Other preservatives includenitrites,sulphites,sorbates,benzoates andessential oils.[5]
Spoilage bacteria andlipid oxidation usually need oxygen, soreducing the oxygen around fish can increase shelf life. This is done bycontrolling ormodifying the atmosphere around the fish, or byvacuum packaging. Controlled or modified atmospheres have specific combinations of oxygen, carbon dioxide and nitrogen, and the method is often combined with refrigeration for more effective fish preservation.[5]
Two or more of these techniques are often combined. This can improve preservation and reduce unwanted side effects such as thedenaturation of nutrients by severe heat treatments. Common combinations are salting/drying, salting/marinating, salting/smoking, drying/smoking, pasteurization/refrigeration and controlled atmosphere/refrigeration.[5] Other process combinations are currently being developed along themultiple hurdle theory.[11]
See:
| Fish | |
|---|---|
| Shellfish | |
| Other seafood | |
| Processed seafood | |
| Seafood dishes | |
| Health hazards | |
| Advisory services | |
| Animal welfare | |
| Related topics | |
