Types of fish, composition and nutritive value, judging the freshness of fish, fish grading and cooking of fish, smoking, pickling, salting and dehydration, preservation of fish and processed fish products

 

Types of fish, composition and nutritive value, judging the freshness of fish, fish grading and cooking of fish, smoking, pickling, salting and dehydration, preservation of fish and processed fish products

 

Type of fish

            It is estimated that there are about 25000 spices of fish living today varying in size from very small fishes to very large sharks. They are second to insects in the largeness of population, mammals, and birds and amphibious put together.

About 250 different spices of fishes are used for edible purpose

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Fish are broadly classified as Finfish and Shellfish

 

Finfish---fishes having vertebrae with fin-appendages, which help balance and steer body in its movement’s f these fishes is covered with protective seals and is abundantly coated with miscues.

Finfish are divided into white fish and oil-rich fish.

White Fish

White fish are sometimes referred to as "lean fish" because all the oils are contained in the liver, which is removed during gutting. White fish are further sub-divided into:

• Round White Fish
  Examples include cod, haddock, hake and pollock
• Flat White Fish
  Examples include plaice, lemon sole, brill, turbot, black sole are common examples of this category
• Cartilaginous Fish
  Ray, rock salmon and shark are examples

Oil-Rich Fish

Oil-rich fish are so called because the oils are distributed throughout the flesh of the fish. Mackerel, herring, salmon and trout are common examples.

Occasionally you will find fish classified in a different way: Demersal and Pelagic Fish. Demersal fish are those which live on or near the sea bed. Round and flat white fish fall into this category. Pelagic fish swim in mid-waters or near the surface. Oil-rich fish such as mackerel, herring and tuna are common examples.

Shellfish (inverteabre)

Shellfish are broadly divided into two main categories: Molluscs and Crustaceans.

Molluscs

Molluscs can be divided into three categories:

• Uni-valve Molluscs
  Uni-valve molluscs are those with one shell – periwinkle and whelks.
• Bi-valve Molluscs
  Bi-valve molluscs are those with two shells hinged at one end – mussels, oysters and scallops are good examples.
• Cephalopods
  this type of shellfish has no outer shell, but just a single internal one called a pen. Examples include squid and cuttlefish.

Crustaceans

Crustaceans are more mobile creatures with hard segmented shells and flexible joints. Examples include prawns, shrimp, crab and lobster.

 

            The kinds of finfishes available for food are more than those of shellfish. They are found both in salt water and fresh water. Their flavour and quality depends partly on the water in which they are grown. Saltwater fish have a more distinctive flavour than fresh water. The common sea or marine fishes available in the country are all types of shark, salmon, Bombay duck, ribbon fish, tuna etc.

            Fish are also classified based in their fat content as lean (less than 2 % fat) medium (2-5%) and fat (more than 5%) fishes. Bombay duck, halibut, cod and sole are example of lean fishes. Fat fish include salmon sardine, tuna etc. in fish more than 5 % fat in the edible flesh, the flesh is usually more highly pigmented than that of the low fat verities which are generally white fleshed.

 

 

 

 

C

omposition of fish

 

 

The principal components of fish muscle

Water

The main constituent of fish flesh is water, which usually accounts for about 80 per cent of the weight of a fresh white fish fillet. Whereas the average water content of the flesh of fatty fish is about 70 per cent, individual specimens of certain species may at times be found with water content anywhere between the extremes of 30 and 90 per cent.

The water in fresh fish muscle is tightly bound to the proteins in the structure in such a way that it cannot readily be expelled even under high pressure. After prolonged chilled or frozen storage, however, the proteins are less able to retain all the water, and some of it, containing dissolved substances, is lost as drip.

Protein

The amount of protein in fish muscle is usually somewhere between 15 and 20 per cent, but values lower than 15 per cent or as high as 28 per cent are occasionally met with in some species.

Two essential amino acids called lysine and methionine are generally found in high concentrations in fish proteins, in contrast to cereal proteins for example. Thus fish and cereal protein can supplement each other in the diet. Fish protein provides a good combination of amino acids which is highly suited to man’s nutritional requirements and compares favourably with that provided by meat, milk and eggs.

Fat

The fat content of fish can vary very much more widely than the water, protein or mineral content.  The fat percent in the fish is about 0.1 % to 5%. The fat of fish is rich in poly-unsaturated fatty acid/PUFA which is very beneficial for the health. The fat content of fish is less as compared to meat and poultry

In white fish of the cod family, the fat content of the muscle is always low, usually below 1 per cent, and seasonal fluctuations in fat content are noticeable mainly in the liver, where the bulk of the fat is stored.

The minor components of fish muscle

Carbohydrates

The amount of carbohydrate in white fish muscle is generally too small to be of any significance in the diet; hence no values are given in the tables. In white fish the amount is usually less than 1 per cent, but in the dark muscle of some fatty species it may occasionally be up to 2 per cent. Some molluscs, however, contain up to 5 per cent of the carbohydrate glycogen.

Minerals

The fresh water fish are rich in cooper, sulphur, and phosphorus but marine fish is rich in Iron and iodine.

Vitamins

The oil extracted form the lever of the fish is rich in vitamins, those that are soluble in fat, such as vitamins A, D, E and K, and those that are soluble in water, such as vitamins B and C.

 

H

ow to judge quality in fresh seafood

 

            Fresh fish as other fish spices are material which fast deteriorates. This implies that both the producer and the consumer are very often exposed to the risk of buying fish which is not fresh or has even deteriorated. Knowledge of the average shelf life for individual fish species depending on storage condition

Appearance

• Look for bright, clear eyes. The eyes are the window to a truly fresh fish, for they fade quickly into gray dullness. Dull-eyed fish may be safe to eat, but they are past their prime. Oysters, mussels and pipis should be alive when sold in the shell.
• Next look at the fish. Does it shine? Does it look metallic and clean? Or has it dulled or has discolored patches on it? If so, it is marginal      
• The flesh of raw seafood is translucent or white, and firm and springy to the touch; it should not be soft or mushy.

• Look at the gills. They should be a rich red. If the fish is old, they will turn the color of faded brick.
• Look for vibrant flesh. All fish fade as they age. If the fillet still has skin, that skin should look as pristine as the skin on an equally good whole fish – shiny and metallic.
• Is there liquid on the meat? If so, that liquid should be clear, not milky. Milky liquid on a fillet is the first stage of rot

Smell

1. The smell of raw and cooked seafood is a reliable guide to quality because spoiled seafood has a strong offensive smell.
2. Fresh food has a pleasant, mild flavour which differs from group to group (fish,     molluscs, and crustaceans) and from species to species.
3. Fresh seafood has the mild, distinctive seaweed smell of the sea. However, smell   alone cannot be used to detect stale seafood and therefore appearance and smell   should both be considered when judging quality.

Taste

1. Fresh food has a pleasant, mild flavour which differs from group to group (fish,     molluscs, and crustaceans) and from species to species.
2. The taste of fresh seafood is a good guide to freshness because flavour gradually   disappears during storage.
3. Stale seafood does not have the characteristic flavour of the species, and is often   tasteless. Although the animals come from the sea, fresh seafood does not have a salty taste. In fact, most consumers add salt when cooking fish and shellfish.

Texture

1. The flesh of fish is juicy and tender and only rarely is it tough.
2. The flesh of prawns, lobsters and squid should be firm but poor quality shellfish    may     be tough.

 

C

ooking Methods

Cooking methods adopted for meat are applicable for fish cooking. When sufficiently cooked, the flesh of fish can be easily separated into flakes. Thus fish is to be carefully handled during cooking. Fish is generally cooked by dry heat such as baking, and frying. Moist heat methods such as steaming and pouching are also used. Some fishes are rich in fat and such fishes required very little additional.

The following are the main cooking methods used for fish.

1. Poaching

Most kinds of fish can be cooked in this way. Immerse fish in simmering, seasoned liquid like stock or milk and poach gently for 5-8 minutes, depending on the thickness of the fish. The liquid is ideal for use in sauces and soups.

When poaching smoked fish, place it in cold unsalted water and bring it to a steady simmer. This liquid will be salty and may not be suitable for re-use.

Almost any fish may be gently cooked in heated liquid, such as wine, water, fish stock, or milk.

• Pour just enough liquid to cover the fish.
• Cover the pan tightly and cook fillets just below the boiling point.
• Cook fillets 8 to 10 minutes and whole fish 15 to 20 minutes.
• The poaching liquid may be used as the base for a sauce.

 

2. Steaming

Small whole fish or fillets are good cooked in this way. Flavour can be added by using different cooking liquids but usually the fish is seasoned. Place it in a steamer, cover it tightly and cook over simmering water for 10-15 minutes depending on the thickness of the fish or the fillets. If a steamer is not available fish can be steamed between two plates above a pan of boiling water.

3. Grilling

Grilling is cooking under a radiant heat and is a fast and convenient method of cooking. Suitable for fillets or small whole fish. When grilling whole fish cut through thickest part of the fish to allow even cooking. Lightly oil and season fish or fillets and, to avoid breaking, do not turn more than once.

hicker cuts of fish steak (tuna, salmon, halibut or swordfish) grill more successfully than leaner fish. Use a clean, oiled, closely spaced grill grate. For smaller fish, a fish grill basket will provide the best results.

• Heat charcoal 30 minutes or gas grill 10 minutes on high with lid closed. For indirect heat method, build fire or heat grill on one side only.
• Brush grill grate generously with oil to prevent fish from sticking; grate should be 4 to 6 inches from heat source.
• Place fish on grill rack in a single layer.
• For direct heat method, cook fish 4 to 6 minutes per side (per inch of thickness) over medium to medium-high heat or until done.
• For indirect heat method, place fish on grate over cool side of grill and cook 15 minutes with lid closed. Or sear fish on grate over heat, then move to cool side of grill to finish cooking.
• For grill temperature, place a grill surface thermometer on grate or use the hand-count method to determine temperature: Hold the palm of your hand just above grate at cooking height. If heat causes you to pull away in 3 seconds, heat is medium-high (425°F grill surface temperature); if heat causes you to pull away at 4 seconds, heat is medium (375°F).

 

4. Barbecuing

This is cooking over a radiant heat - usually a charcoal or gas barbecue. It is fast and popular during fine summer weather. Oil-rich fish are suitable for barbecuing as the natural oils keep the flesh moist. Baste whitefish often to keep it moist. Protect the fish from strong heat and from breaking up by using foil or special wire holders.

5. Baking

All kinds of fish can be baked in the oven. Fish should be covered to prevent drying, either with a lid, foil or greaseproof paper. It may be baked with stuffing, on a bed of vegetables, in a pie or sauce.

• Heat oven to 450°F.
• Spray a baking sheet or shallow baking dish with non-stick cooking spray.
• Place fish on baking sheet in a single layer, season as desired.
• Bake uncovered, 10 minutes per inch of thickness or until fish is done.

 

6. Braising

This is an "all-in-one" method of cooking where the fish is cooked together with vegetables, either on the hob or in the oven. Lightly sauté the selected vegetables. Add the fish, seasonings and liquid. Cover and cook until fish is cooked through.

7. Frying

Frying is probably the most popular method of cooking fish.

Shallow/ Pan frying: The fish should be seasoned and lightly coated with flour or crumb before frying to protect it and seal in the flavour. Use a mixture of oil and butter when frying and turn the fish only once during cooking, to avoid breaking up. This technique results in food that's crisply tender. Seafood best suited to this technique includes fish fillets, shrimp, bay scallops, and slipper tails. Firm fish, such as cod or halibut, may also be cut into strips and stir fried.

• Heat 1/4-inch oil or butter in a nonstick skillet over medium to medium-high heat.
• Fish may be dipped in milk or beaten egg and then breaded.
• Cook fish 4 to 5 minutes per side (per inch of thickness) or until done.

 

Deep Frying: The fish should be seasoned and coated before frying, usually with a batter or an egg and breadcrumb mixture. Use a suitable container and heat the oil to 190°C/375°F. Test the temperature before cooking fish. Drain the fish after cooking on absorbent paper. Fish 1/2-inch thick is ideal for this method. Monitor oil temperature with a candy thermometer to ensure proper cooking: If oil is too cool during cooking, food will become soggy and greasy; if oil is too hot, food will become too dark or burned on the outside before the inside reaches the proper temperature.

• Heat enough vegetable or canola oil to 350 to 375°F to allow the fish to float once it's done.
• Cut thicker fish into smaller chunks so fish will cook in the time it takes to brown.
• Sprinkle fillets lightly with flour. Dip in beaten egg. Coat with your favorite breading.
• Cook 3 to 5 minutes until lightly browned.
• Make sure pieces do not touch while frying. This could create steam, which causes a "soggy" coating.
• Drain on paper towel before serving.

            Stir Frying: This is a very fast and popular method of cooking. Use a wok or deep frying pan and a             high cooking temperature. Food should be cut into thin strips and prepared before cooking begins.             This is a very suitable method of cooking firm-fleshed fish.

8. Microwave Cooking

Fish cooks perfectly in a microwave oven because of its high water content and loose texture. Use a non-metallic dish and arrange the thickest part of fish towards the edge of the dish. Fold tail pieces underneath to prevent uneven cooking. As cooking will continue when removed from the oven, allow the fish to stand for 2-3 minutes before serving

S

moking of fish

Foods have been smoked by humans throughout history. Originally this was done as a preservative. In more recent times fish is readily preserved by refrigeration and freezing and the smoking of fish is generally done for the unique taste and flavour imparted by the smoking process.

            "The process of smoking fish occurs through the use of fire. Wood contains three major components that are broken down in the burning process to form smoke. The burning process is called pyrolysis, which is simply defined as the chemical decomposition by heat. The major wood components are cellulose, hemi cellulose and lignin. Higher fat fish absorb smoke faster and have bet-ter texture after smoking than lower fat fish

"The major steps in the preparation of smoked fish are

1. Cleaning and splitting
2. Salting (bath or injection of liquid brine or dry salt mixture)
3. Hanging
4. Smoking
5. Cooling
6. Packaging (air/vacuum or modified), and storage.      

 

Preparation (Cleaning and splitting)

 

            Different species of fish require different preparation techniques. Salmon are usually prepared by removing the backbone and splitting. Bottom fish are filleted. Small fish such as herring and smelt should be headed and gutted before brining. Use good quality fish because smoking will not improve fish quality; in fact, it may cover up certain conditions that could create food safety problems later.

            Clean all fish thoroughly to remove blood, slime, and harmful bacteria. Keep fish as cool as possible at all times, but do not refreeze. When you cut fish for smoking, remember that pieces of uniform size and thickness will absorb salt in a similar way, reducing the chance that some pieces of fish will be either under- or over-salted. Do not let fish sit longer than 2 hours at room temperature after cleaning and before smoking.

 

Salting

Salt preserves smoked fish by reducing the moisture content. However, without chemical analysis, it is hard to be certain that a fish has absorbed enough salt. That is why proper cooking and refrigerated storage are essential for safety. Salt the fish before smoking in a strong salt solution (brine). Salting fish in a brine that is 1 part table salt (non-iodized and with no antcaking agent) to 7 parts water by volume for 1 hour will work in most cases. (This proportion will read approximately 60° SAL on the scale of a salometer.) A salometer is an instrument that can be purchased from a scientific supply store or a salt manufacturer for measuring the salt concentration of brine.

 

A gutted herring requires about 30 minutes brine time in a refrigerator; large or oily fish require about 2 hours. Decrease the brine time for low fat and skinned fish. A smoked fish with a definite but not unpleasantly high salt flavor probably has absorbed enough salt. Dry salting techniques are acceptable.

 

Hanging

Once the brining period is complete, rinse the fish surface and allow it to air dry meat side up on a greased rack in a cool place until a pellicle(A pellicle is a shiny, slightly tacky skin that will form on the meat surface of your fish) forms (i.e. ,at least 1 hour) before smoking. The length of smoking time depends on the flavor and moisture level of the product.  Smoke your fish for up to 2 hours at around 32.3°c in a smoker, and then increase the heat until the fish reaches a temperature of at least 65.55°c (preferably 71.2°c) and cook for at least 30 minutes

Smoking

Today there are two main methods of smoking fish: The traditional method (cold (28–32°C)) and the mechanical method (hot (70–80°C)). Cold smoking does not cook the flesh, coagulate the proteins, inactivate food spoilage enzymes, or eliminate the food pathogens, and hence refrigerated storage is necessary until consumption." In this method fish being suspended in smokehouses over slowly smouldering saw dust. The fish are left overnight to be naturally infused with smoke. In the mechanical method smoke is generated through the use of smoke condensates, which are created by the industrial process of turning smoke into a solid or liquid form.. But both require careful control of temperature, humidity and processing time. Proper sanitation and cold storage after processing are also essential.

 

Cold smoking

Cold smoking is exactly what it sounds like. Cold-smoked fish are not cooked, because the temperature generally does not exceed 43° C. To maintain the proper temperature, ensure uniform drying and preserve the desired color, it is necessary to use an indirect source of heat and smoke

Proper cold-smoking often takes less than 24 hours, during which the relative humidity should at first be maintained at about 90% to facilitate smoke absorption but subsequently dropped to about 70% to achieve the required amount of drying. If humidity remains much higher than 70% during the drying period, the drying will be too slow. If it is considerably lower, the fish dry too quickly, resulting in case hardening and poor smoke absorption.

It has been recommended by some health regulatory agencies that cold-smoked products should have a minimum water phase salt concentration of 3.4% to assist in preventing the growth of Clostridium botulinum. Following smoking, the products should be frozen or stored at or below 3° C. Typical weight losses range 40 to 45%.

 

Hot Smoking

Hot smoking is the process used in the majority of smoked fish products. Hot-smoked products are fully cooked and can reach temperatures as high as 82° C. Because of the high temperatures, hot smoking takes only a short time, depending on the internal temperature of the product.

Different species of fish tolerate heat differently, so the hot smoke process is not the same for all products. Hot-smoked fish are moist and juicy when properly finished.

 

Cooling

Whether cold smoking or hot smoking, the product must be cooled immediately after smoking. Hot-smoked products require more cooling, so it is expected that cold-smoked products will cool at least as efficiently.

Finished products should be cooled to a temperature of 10° C or less within three hours after cooking and further cooled to 3° C or below within 12 hours. This temperature should be maintained during all are fully cooked but have a relatively short shelf life and must be refrigerated subsequent storage and distribution. Smoked fish should never be packaged hot, because excessive condensation can form inside the package.

 

Packaging

Most smoked fish products, unless canned and sterilized by retorting, have about the same or slightly longer shelf life than fresh fish. It should be kept frozen or under refrigeration just above freezing temperatures.

 

Storage

If storage temperatures rise above 3° C, there is a risk that Clostridium botulinum may grow and produce toxins in some types of smoked fish. By removing air, vacuum or gas packaging can provide a favorable environment for the growth of this organism.

 

S

alting of fish

            Salting of fish is a traditional processing method in most countries of the world. The presence of sufficient quantities of common salt (sodium chloride) in fish can prevent, or drastically reduce, bacterial action. When fish are placed in a strong solution of salt (brine) which is stronger than the solution of salt in the fish tissue, water will pass from the tissue into the brine until the strength of the two solutions is equal.

At the same time, salt will penetrate into the tissue. This phenomenon is known as osmosis. A concentration of between 6 and 10 per cent salt in the tissue will prevent the activity of most spoilage bacteria; the removal of some water from the tissue during the salting process will also reduce the activity of the spoilage bacteria.

If fish are salted before drying, less water needs to be removed to achieve preservation. A water content of 35 - 45 per cent, depending on the amount of salt present, will often prevent, or drastically reduce, the action of bacteria.

Fish to be cured are usually first cleaned, scaled, and eviscerated. Fish are also salted by packing them between layers of salt or by immersion in brine.

The fish most extensively salted are cod, herring, mackerel, and haddock. The use of heat or smoke during processing, and subsequent storage at refrigerated temperatures are not always effective by themselves in the control of micro-organisms.

Preparing Before Salting

1.      Remove the entrails, clean, and remove head and scales from whole fish.

2.      Remove backbone in large fish by cutting length- wise. This is not necessary on small fish such as herring.

3.      Dry salt or brine cures 5–8 days. Salted fish may be stored in a cool place (preferably under 50˚F) for 2–3 months before pickling (6–12 months under refrigeration).

4.      all impurities, blood and slivers should be removed;

5.      The waste should be removed continuous from the line; any damaged, contaminated or otherwise unacceptable fish should be discarded before splitting;

Methods / types of Salting

1.      Dry Salting

2.      Wet/ Brine Salting

3.      Kehch Salting

4.      Mixed /Pickling Salting

 

 

 

 

 

 

 

 

 

 

 

Dry salting- This is the most widely used method of fish curing. All types of fishes except fatty fishes, big or small are cured by this method. Here, the fish is gutted, beheaded or ventrally split open and the viscera removed. The fish is then washed clean. Larger fishes are dorso ventrally split open and cleaned thoroughly. Scores are made also the thick flesh portion for better penetration of salt. Salt is then applied in the ratio 1:3 to 1:10 (salt to fish) depending upon the size of the fish. The fish is then stacked in clean cement tanks or other good containers. The bottom of the tank is covered with salt and a layer of fish is placed. Both fish and salt are alternately placed in the tank and wooden planks are put on the top and weighed down. The salt draws out the water in the fish and the weight placed keeps it under pressure. The fish is kept in this condition for 24-48 hours. After this the fish is taken out, washed in brine to remove adhering salt and trained. It is then hygienically dried in the sun preferably on clean racks. Yield of the product by this method is about 35-40%. This product has a shelf life of 6-10 weeks.

If fine grain salt is used directly on a fish, it may cause a rapid removal of water from the surface which becomes hard and prevents the penetration of salt to the inside of the fish; this condition is called 'salt burn'. For dry salting, a mixture of large and small grain sizes is recommended.

 

 

 

 

 

 

 

 

Brine/Wet salting-The initial stages of processing and salting are the same as for dry curing. Once the fish is put into the tank it is allowed to remain in the self-brine. The fish is not dried at all. The wet fish is then drained and packed in palmyrah leaf baskets, container that has a lid or coconut leaf baskets and taken to the market. The fish is taken out only when there is demand. This method is particularly suitable for fatty fishes. This is mainly done for fishes like oil sardine, mackerel, ribbonfish etc. In such fishes the fat gets oxidized on exposure to air. These products have moisture content of 50-55% and the salt content around 25%. They are most susceptible to fungal attacks, bacterial degradation and general putrefaction. They have a very short shelf life.

Use about equal volumes of fish and brine. Place the top layer of fish skin side up. Hold under refrigeration if possible. Do not store above 10˚c.

 

Pickle/Mixed salting - Pickle curing is a type of wet salting where the fish is layered by granular salt which, dissolves in the surface moisture of the fish forming solution which penetrates into the fish removing moisture from the fish. The fish is allowed to remain in this self brine. In this process if the fish are not completely covered in 3 - 4 hours, saturated brine is normally added to completely immerse them. A cover should be placed on top of the fish to hold them below the surface of the pickle. The presence of impurities may reduce the actual concentration of sodium chloride in solution and, in practice, the brine strength ranges between 80 and 100 per cent, which corresponds to 270 - 360 grams of salt to each litre of water.

 

Dry or Kench Salting - In this method, salt is rubbed on to the surface of the fish and stacked in layers of salt and fish. The self-brine formed is allowed to drain away. This method cannot be recommended for general use in the tropics as the fish are not covered by the brine or pickle and are therefore more susceptible to spoilage and insect attack. Exposure to the air and the presence of salt also encourages the rate of fat oxidation which gives rise to discoloration and the characteristic rancid flavours.

 

Spoilage of salted fish

 

            Although salt prevents the growth of spoilage bacteria, other micro-organisms are not so affected by             the presence of salt. Micro-organisms can be conveniently divided into three groups by their             sensitivity to salt:

1.        Low tolerance - growth is stopped, or the organism is killed, by the presence of low concentrations of salt. Most of the normal spoilage organism’s fall within this group and a salt content of a few per cent will prevent growth.

2.        High tolerance - organisms which can tolerate high concentrations of salt although the rate of growth is usually reduced, or stopped, at very high salt concentrations.

3.        Halophiles - those organisms which cannot grow without salt. With dry salted fish, the salt-tolerant and halophilic organisms can continue to grow but they cannot do so in pickle-cured products: most of them are aerobic organisms and the fish and brine of pickle-cured fish contains very little, or no, oxygen.

4.        Most enzyme activity is stopped in heavily salted fish but, with lighter cures, the fish may develop characteristic flavours as a result of enzymic activity and the growth of certain salt-tolerant organisms. If the salt levels and fermentations are not carefully controlled, putrefactive spoilage may occur.

 

Uptake of salt by fish

Several factors which affect the rate at which salt is taken up and water is replaced in fish are:

1. the higher the fat content, the slower the salt uptake;
2. the thicker the fish, the slower the penetration of salt to the centre;
3. the fresher the fish, the more slowly salt will be taken up;
4. The higher the temperature, the more rapid the salt uptake.

 

 

P

ickling

 

 

Traditionally, pickles made of vegetables like lime; gooseberry, ginger, garlic etc. are used as an important side dish along with meals. Though such pickles made of fish or meats were practically unknown in the past, such products have now become very popular and products under several brand names are now available in the market.

Method of Preparation

1.      Fish is cut into pieces and cleaned with potable water. Cut fish into bite-size pieces or strips, as desired.

2.      Mix the fish thoroughly with 3% of its weight of salt, chilli powder, turmeric and keep for two hours. Light salted and partially dried fish also may be used.

3.      Fry the fish in minimum quantity of oil. Set apart the fried fish.

4.      Fry the ingredients (mustard, green chillies, garlic, ginger) in the remaining quantity of oil and then add chilli powder, pepper powder and turmeric powder and mix well over low flame for a few minutes.

5.      Remove from fire,

6.      When cooled, add vinegar, powdered cardamom, clove, cinnamon, sugar and remaining salt and mix thoroughly.

7.      Heat about 80 degree C.

8.      The mixture is cooled at room temperature.

9.      Transfer to clean, sterile g1ass bottles and seal with acid proof caps. Take care to see that there is a layer of oil over the contents in the bottle.

10.  Flexible pouches made of 12 micron polyester laminated with l 18micron LD-HD co-extruded film can also be use for packing the pickle.

Precautions

1.      Do not use less than one part vinegar to one part water.

2.      Do not pack fish tightly into jars.

3.      The fish must be stored under refrigeration (3˚c) to provide an added measure of safety. This will ensure that food poisoning bacteria will not grow. Refrigerated storage also will retard bacterial spoilage, reduce problems with enzymatic softening, and reduce discoloration.

4.      If refrigeration facilities are limited, do not pickle more fish than you can consume in a few weeks.

 

D

ehydration of fish

 

Drying is the removal of water from fish. Normally the term 'drying' implies the removal of water by evaporation but water can be removed by other methods: for example, the action of salt and the application of pressure will remove water from fish. Since water is essential for the activity of all living organisms its removal will slow down, or stop, microbiological or autolytic activity and can thus be used as a method of preservation.

            Traditional method of preserving fish, the action of the sun and wind but the controlled artificial dehydration of fish has been developed in some industrialized countries

            If the moisture content of fresh fish is reduced during drying to around 25%, bacteria cannot survive and autolytic activity will be greatly reduced, but to prevent mould growth, the moisture content must be reduced to 15%. The presence of salt retards bacterial action and, in addition, it aids the removal of water by osmosis. When salt is added to fish before drying, a final moisture content of 35 - 45% in the flesh, depending on the salt concentration may be sufficiently low to inhibit bacteria.

            In any process of drying, the removal of water requires an input of thermal energy. If the outward movement of water occurs in the following sequence:

• migration within the material to the surface
• removal from the surface
• mixing with the atmosphere surrounding the material
• removal from the vicinity of the surface, it must be accompanied by the inward transfer of heat in the following sequence: emission from the heat source
• transfer to the surface of the material
• conduction within the material
• Provision of latent heat of evaporation and the partial enthalpy of dilution of the system which is regarded as a solution.

Factors influence the rate of drying:

1. Relative humidity (RH) of the air
2. Air velocity
3. Air temperature
4. Surface area of the fish
5. The nature of the fish: a high fat content in the fish retards the rate of drying.
6. The thickness of the fish: the thicker the fish, the further the water in the middle layers has to travel to reach the surface.
7. Temperature of the fish: diffusion of water from the deeper layers to the surface is greater at higher temperatures.
8. The water content

Dehydration procedure

1. Wash the fish thoroughly.
2. Open the belly cavity and the visceral organs.
3. Rinse the fish in running water. Drain.
4. Mix 10% brine solution (1 part salt to 9 parts water).
5. Soak the fish in a 10% brine solution of salt for 30 to 40 minutes.
6. Drain the fish and wash thoroughly.
7. Place the salted fish in woven bamboo racks to dry under the sun or solar dryer for 2 to 3 days.
8. Let cool, then place in clean boxes or baskets or wrap them in wax paper.
9. Store in a cool place.

 

Drying of fish: methods

Solar driers

            Considerable interest has been shown in the development of solar powered driers in recent years. In these, the energy of the sun is collected and concentrated to produce elevated temperatures and an increased rate of drying. Raising the air temperature increases the amount of water the air can hold, thus the relative humidity will be reduced and the air will be able to absorb additional water vapour. In the humid tropics, the relative humidity is often too high for rapid natural drying and it is hoped that solar powered units which are simple, inexpensive and efficient can be developed for drying fish

 

Mechanical driers

Several types of mechanically powered driers have been developed and used commercially in different parts of the world. Fish are dried in a fan driven air-stream; the air is usually heated and, in some cases, the air can be recirculated to control the relative humidity.

 

Freeze drying

            Evaporation of moisture from fish placed in a vacuum quickly cools the fish due to the transfer of heat energy. The fish freeze after about 15 per cent of the water has evaporated. For rapid freeze drying, some heat must be supplied to the fish if evaporation is to proceed at a rapid rate. Moisture must also be removed from the vacuum chamber, otherwise it will become saturated and no further drying will be possible.

            Freeze drying requires a high energy input and is only feasible for very high value products. Freeze dried products have the advantage that they can be stored under ambient conditions as long as the packaging is impervious to water.

The process of freeze drying

Developing the above principles, the freeze drying process involves:

 

1. Placing the material to be preserved onto the shelves when it is still unfrozen.
2. Which is then sealed, when you seal the chamber and begin the process, the machine runs the compressors to lower the temperature in the chamber. The material is frozen solid, which separates the water from everything around it, on a molecular level, even though the water is still present.
3. The machine turns on the vacuum pump to force air out of the chamber, lowering the atmospheric pressure below .06 ATM.
4. The heating units apply a small amount of heat to the shelves, causing the ice to change phase. Since the pressure is so low, the ice turns directly into water vapor. The water vapor flows out of the freeze-drying chamber.
5. This continues for many hours (even days) while the material gradually dries out. The process takes so long because overheating the material can significantly change the composition and structure.
6. Once the material is dried sufficiently, it's sealed in a moisture-free package.

 

Advantages

1.      No shrinkage - the freezing of the food effectively fixes its shape.

2.      No case hardening - there is no water movement to carry soluble to the surface; the ice directly sublimes from within the food as the drying front penetrates.

3.      No thermal damage - no high temperatures to cause loss of flavour or development of 'burnt' flavours.

4.      Rapid rehydration - because a very open texture is obtained.

Disadvantages

These all relate to the economy of the process and the storage and distribution of the end product.

(a) Primary cost. - The equipment is sophisticated and expensive.

·         The chamber (which is required by any mechanical drying method) has to be very strong: it must be capable of withstanding the pressure differences. The seals on the door must be airtight to ensure that low pressures are easily maintained.

·         The low pressure required necessitates sophisticated vacuum equipment, steam ejectors and/or heavy duty piston pumps. If the latter are used, a vapour removal system is required between chamber and pumps.

·         Some system is required to provide heat to the food during the drying process.

·         To maximize the capacity of the system, it may be desirable to freeze the product before drawing a vacuum, either within the chamber or in a separate process.

(b) Operating costs. - In addition to the energy of evaporation (which is required by all drying processes),             energy is required to develop and maintain the vacuum and for any refrigeration facility (to pre-freeze             and perhaps to recondense vapour to stop it getting through to a piston vacuum pump).

• A high level of competence is required in operators and service engineers: there is, therefore, a relatively high labour cost.
• The technology is advanced: therefore, repair and maintenance costs (spares) are high, compared to more conventional drying systems.
• It is a batch process: there are periods of loading/unloading when equipment is unoperational.

(c) End product.

            The high prime and operating costs mean that this process is only suitable for high value foods which             can carry a high production cost. However, the consumer expects good quality from high cost goods.

• The lack of shrinkage and case hardening associated with very low moisture content means that freeze dried foods are very brittle and so need to be protected by rigid packaging.
• The open structure and low water content mean that freeze dried foods are very vulnerable to oxidative deterioration and so, as already mentioned, gas tight packaging associated with inert gas purging is often adopted.

 

P

reservation of fish

 

Fish are an extremely perishable foodstuff. Spoilage occurs as the result of the action of enzymes (autolysis) and bacteria present in the fish, and also chemical oxidation of the fat which causes rancidity. Fish invariably become putrid within a few hours of capture unless they are preserved or processed in some way to reduce this microbial and autolytic activity and, hence, retard spoilage.

 

Freezing- is the simplest and the most natural way of preserving fish. Freezing is very easy and safe to do, The following are the simple steps to follow in freezing fish:

1. Select fresh fish for freezing.

2. If the fish are small like dilis, wash and freeze right away. If fish are large like bangus, remove scales, entrails, and trim fins and tail and wash.

3. Wrap fish in plastic wrap or put in container packed tightly to eliminate air.

4. Label wrapped fish or container with name and date.

5. Freeze immediately.

 

Smoking-Smoking is a slow way of broiling and has very little preservative action. Smoking adds a distinctive flavor. Here, the fish is placed in close proximity to the fire and the fished is cooked and saturated with smoke. It is sometimes called “barbecue smoking”.

 

Drying or Dehydration-One of the more popular techniques of preserving fish is drying or dehydrating method. It is the removal of moisture in food to them less perishable. Drying or dehydration provides the following advantages:

a) Dried food requires less storage space than other types of food.

b) Dried food weighs much less than the equivalent amount of canned products.

c) Food can be preserved without the addition of sugar or any other preserving agent.

F

ish canning- Canning is a relatively modern technology which enables man to preserve food in an edible condition under a wide range of storage conditions for long periods - from a few months to several years. Essentially, the process involves hermetically sealing the food in a container, heat 'sterilizing' the sealed unit and cooling it to ambient temperature for subsequent storage.

 

DESCRIPTION OF THE PROCESS:

 

Selection on raw material-

Mature, pre-spawning fish and medium fatty fish are better for canning. Eventually fish with the following characteristics are used for canning-

– Excess bone

– Taste less

– High fishy odour

– Fish with hard and farm muscle.

– Available Eg: Sardine, Hilsa, Salmon, Herring etc

 

Pre-treatment before canning:

a)      Nobbing: In the case of larger fish, such as herring and pilchard, the head and gut are removed, but not the roe or milt. This process of removing head and gut in one operation is called nobbing.

b)      Washing and de-scaling: The next operation is descaling; remove fins, viscera from the raw materials and washing. Nobbing releases blood that must be removed because it causes brown staining in the processed fish. Washing also removes surface slime and dirty materials from fish.

Pre-cooking

Pre-cooking is usually carried out in steam, water, oil, hot air or smoke, or a combination of these. Precooking is done to remove excess moisture and fat from the fish. This can be achieved by steaming, frying and blanching. By this method the fish becomes firm and also the moisture content comes down. After precooking, fish meat looks bright and more attractive.

However, there will be some loss of taste and flavour components. Precooking by steaming is done in retort for 30-45 minutes which expels moisture and fat and can be removed by draining.

Frying is done using refined vegetable oil at a temperature of 160 to 180oC for one to three minutes. Frying results in reduction in moisture, firming of texture, reduction in size and improvement in taste and flavour.

Blanching is one of the precooking methods where the fish/shrimp is dipped in boiling brine containing 6-8% salt for 4-6 minutes. Use of citric acid in blanching of shrimp is a normal practice to achieve better colouration and texture. Blanching results in contraction and curling of shrimp, reduced moisture content, development of firm texture and attractive colouring. Blanching of shrimp helps in controlling the net weight of shrimp in the processed cans.

Live clams, green mussel, oysters and crab are washed, steam cooked for a few minutes to open the shell and to collect the edible portion. It is essential to remove blood from crab meat which otherwise results in blue discoloration.

In tuna, the precooking operation helps in easy separation of dark and light meat. The dark meat is not packed in can as they are not appealing and normally goes for pet food preparations.

 

Filling and Packing- Fish, being a physically delicate food and, therefore, easily damaged and fragmented by mechanical handling operations, are still largely packed into cans or other retortable containers by hand, with brine, edible oil or sauce which may be metered in mechanically. Often, the fish, after the usual heading, gutting, cleaning and trimming operations, are subjected to pre-processing operations such as salting, brining, drying, smoking, and cooking or a combination of these. Such pre-processing operations have the advantages of:

(a)   Denaturing the proteins and thus rendering the fish muscle firmer and more capable of withstanding handling during the filling operation; and

(b)          Removing water from the fish making them less subject to shrinkage and unsightly aqueous exudation inside the can during heat treatment.

Exhausting - Exhausting is done by the application of heat. By this the gas inside the headspace and between two fish pieces will be removed and a partial vacuum will be formed.

Exhausting is done to prevent-

• Bulging of can

• Oxidation of the food

• Inside erosion of the tin plate.

 

Closing the can:

All fish cans prepared in this country are closed by the double-seaming method and the operation is usually called seaming. A seal must be achieved that will prevent passage of contaminating material, carried either in air or water, into the can after it has been sterilized. Proper care and maintenance of seaming is vital and its performance should be checked at frequent intervals throughout the working day.

Washing:

Washing of can is done by the hot water spray to remove adhering materials.

 

Heat processing

Heat transfer through the fish is by conduction. It is the most important step during the whole canning procedure. It is done for predetermined time at the respective temperature. To fulfill the canning objectives 32 minutes are required at 110⁰ C or 2.5 min is required at 121⁰ C. The temperature of the can is determined a recorder which is called thermo couple. Heat processing is done in a special instrument called retort and so the process is called retorting.

Rotary retort increase in-can heat transfer rates, movement of the headspace bubble during rotation forces an increase in liquid movement and, therefore, convection heat transfer. The fish are more evenly cooked throughout the can and, those nearest the can walls are less likely to be overcooked

Canning involves the even heating of food in tin or glass containers and hermetically sealing canisters. The following steps will contribute to the success of this method:

a)      Careful selection of the raw materials (the kind of fish for preserving)

b)      Check the equipment to be used

c)      Quick preparation to conserve freshness

d)      Provide a time table Cans and jars should be truly hermetically sealed

e)      Store in a cool place

Important consideration in canned fish is the prevention of spores of Clostridium botulinum. Canned fish is a low acid food and C. botulinum is assumed to be in the pack.

 

Cooling:  Cooling is done as quickly as possible after retorting Otherwise off flavour may produce because considerable changes may take place during heat processing.

 

Storage-Cans are usually stored for short periods before marketing. This helps the contents to mature; it also provides a countercheck on the soundness of cans because leaks will show up during this period. Cans should never be stored at freezing temperatures. As a rule cans should be stored at cool, dry conditions. To achieve satisfactory shelf-life the following conditions must be observed:

1. The contents of the cans must be commercially sterilized.
2. The inside of the can must be resistant to and damaging effects from the contents and the outside must be resistant to corrosion under reasonable storage conditions.
3. The can ends must be sealed to prevent ingress of water and/or air or any form of contamination.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Developments in fish canning industry
Year	Development
1817	William Underwood packed lobster in glass containers in Boston.
1824	Salmon canning started at Aberdeen, Scotland.
1843	Mackerel canning
1844	Oyster canning
1864	Fish canning industries started on the West coast of the USA, Canada, Alaska, Russia and Japan.
1867	Dunbars first canned shrimps in Gulf of Mexico.
1870	Canning of sardine became popular in Spain, Portugal and Morocco.
1917	Canning of tuna started in California.
1959	Export of canned shrimps from India.
1970’s	Several shrimp canning industries came up in India.

 

 

 

F

ish Products

 

 

1.      Fish oils- The oils from the fish are obtained by extracting from the entire body of the fish or only from the liver. The oil obtained from the entire body is known as body oils and are grouped into drying and semi drying oils. The drying oil comprises oils of sardine, salmon, herring, mackerel, anchovy, and white fish, while the oils of sprat        and carp constitute semidrying oil due to the low iodine content. The body oil is edible and used for industrial purposes. Liver oil extracted from the liver, is of medicinal importance and contains vitamin A. Freshly extracted oils are differently coloured from colourless to golden yellow, greenish yellow or even red. The oil extracted from             the stale fish is darker in colour and concentration of the oil also varies from fresh to stale along with iodine            content.

2.      Liver Oil- Fish liver oil consists of vitamin A mainly and vitamin D in some species. These vitamins may be formed due to metabolic activities which might have been made their way into the liver and to be stored. Vitamin A mainly gets       stored in the liver. But in large fishes this vitamin gets accumulated in viscera also in addition to liver. The dark coloured liver in sharks yields higher concentration of vitamin A than the light coloured ones. Vitamin A content            of liver lobes are varied markedly in different lobes. Some fish liver oils are rich in vitamin D. Tuna liver oil and   cod liver oil contain 2,50,000; 500 units per gram of oil respectively. Vitamin E in liver oils protects any oxidation of vitamin A.

3.      Cod liver oil- Cod liver oil is obtained from different types of cod fishes like Gadus callarius and Gadus morrhua and other cods. Vitamin A in the oil gets destroyed when exposed to sunlight and the oil becomes thicker when exposed to air. Hence, the oil should be properly stored to avoid the destruction of vitamin A by addition of certain preservatives like nordihydrogualaretic acid (0.05%) and ascorbyl palmitate (0.01%). In view of rich concentration of vitamin A and D with digestible fat, it is found to improve nutrition and calcification in patients           with rickets and tuberculosis when used. It can also be used as supplement for children and can be applied to     wounds and burns.

4.      Shark liver oils- Sharks of Indian waters except few are considered highly important from the yield point of oil from liver which consist of high vitamin A potency. (av. 12,000 IU/g of oil). Oils as rich as 3,00,000 IU/g. have been obtained. The freshly extracted oil is yellow, orange or brown in colour with mild fishy odour, and low acidity. The dilute            shark liver oil is prepared by the addition of refined groundnut oil with vitamin D.

5.      Fish flour- It is possible to extract oil and fatty substances from ground fish tissue by solvent extraction to such an extent         that no fishy order or flavour remains. Fish meal is prepared by solvent extraction process on commercial scale. The fat extracted tissues after stripping off solvent dehydrated and milled. This can be blended with wheat or     maize flour and is used as enriching component in bread, biscuits, cakes, sweets and soups. It forms an ideal     protein supplement to human diets. It contains 85-90% protein

6.      Fish sausage- Fish flesh is ground and mixed with sugar, fats, masala and preservatives. Small bags are prepared with above mixture and boiled to prepare fish sausage.

7.      Fish proteins- The proteins of the fish have high digestibility, biological and growth promoting value. Hence, it plays an important role in human nutrition. The available amino acids are more evenly balanced than the other proteins of animal origin. Amino acids like lysine and methionine are rich in fish protein. In general, fish protein is somewhat superior to egg albumen, bean protein and casein and perhaps equal to chicken proteins. 15 - 25 per cent of protein is obtained from the fish muscle which forms the chief source. The fish proteins are extracted with dilute caustic soda solution from fish fillets or waste after removing the fat. The extracted material         is dried after neutralization. This powder is white in colour without any fishy odour and taste containing 80 - 90           per cent of solubilized protein. This is used as a substitute for white of the egg in baking, confectionary, ice         cream and pharmaceutical products.

.

 

Exercise

 

What is basis of preservation by salting?
When salt introduced into the flesh in sufficient quantity, it delays the activity of bacteria or even inactivates them and reduces enzymatic action by reducing the water activity. Loss of water due to salting and reduced water activity limits bacterial growth and enzyme activity, thus preserving the fish. The high salt content prevents the growth of normal spoilage microflora in the fish; but halophiles, which can survive 12-15% of salt, will survive.

 

How salting takes place (Theory of salting)?
During salting osmotic transfer of water out of the fish and salt into the fish takes places, which effect fish preservation. It is based on different factors like diffusion and biochemical changes in various constituents of the fish. Movement of salt molecules from the brine into the fish takes place through a layer of salt solution covering the fish but having a salt concentration below that of the brine. This layer is formed because the water diffuses out at a faster rate during the initial stages from the fish than the salt solutes, which enters the fish. As the period proceeds the thickness of this covering layer diminishes as its salt content grows. At this point, diffusion of water from the fish ceases and the salt concentration in the layer equals to that of the salt concentration in the in the brine solution. Penetration ends when the salt concentration of the fish equals that of the surrounding medium.

 

What are the factors related to salt to be considered before using for salting?

• Physical properties
• Chemical impurities
• Microbiological contamination

 

What is the principle of preservation by drying?
The moisture content and water activity is reduced and hence microorganisms cannot grow and multiply to spoil the fish. It can be seen that microbiological growth is completely arrested below a water activity level of 0.6 whereas certain other reactions that cause food spoilage continue. Lipid oxidation in fact increases at very low water activity.To understand the concept of preservation by drying we should know about the existence of different forms of water and the concept of water activity.

In what are all the forms the water exists in fish muscle?
Three layers of water exist in food.
• An adsorption layer
• A diffusion layer
• A free layer
Adsorption layer
• Water surround the surface of a colloidal particle
• Water at the adsorption layer is tightly bound to the particle and is called bound water
• It does not take part in any chemical reaction
Diffusion layer
• Less tightly bound to the adsorption layer and the further it is away from it
• More it behaves like free water
Free water
• It has all the properties of ordinary water
• It support the growth of microorganisms
• Take part in chemical reactions
• This form of water is important in the drying process

 

What is smoking of fish?
Smoking of fish refers to subjecting the fish to the smoke generated using various materials such as wood, coconut husk etc.

 

What is cold smoking?
Carrying out the smoking process at a temperature upto 30^oC is called cold smoking, in which cooking of the flesh does not occur. Smoking effect is mainly due to the chemicals killing off the surface bacteria as reduction in water is not significant.
Cold smoked products should be cooked before consumption
Cold smoking takes 2-4 hrs when using a mechanical smoking kiln

What is hot smoking?
Carrying out the smoking process in which the fish is exposed to increasing temperatures up to at least 70^oC is called hot smoking. It is having following effects

• The fish will be cooked
• Enzymes will be destroyed and chemical spoilage will be reduced
• Surface bacteria will be killed

 

How hot smoking is carried out?
In a mechanical kiln, hot smoking is carried out in three stages.

• A preliminary drying period at about 30°C. During this time the skin is toughened to prevent breakage occurring in the remainder of the process.
• A smoking and partial cooking period at 50°C
• A final cooking period at 80°C

The total time could be up to 3 hours. The actual times of each stage will depend upon:

• The species
• The size and thickness
• The fat content of the product
• The loading of the kiln
• The colour and taste requirements

 

How smoking exerts preservative action?
Spoilage of fish can be reduced by reducing some of the important substances like water content, enzyme content and fat content.
The smoking process is effective in reducing the water by evaporation.
This occurs due to:

• The movement of the gases in the smoke over the surface of the fish
• Raising the temperature of the fish

The chemical components such as phenols and formaldehyde exist in the form of vapor in the smoke exert antioxidant and antibacterial activity. In addition the smoking process results in the penetration of the chemicals into the fish and loss of water from the flesh. A layer is formed which reduces the effect of oxygen that enters the fish from the surrounding air. Therefore the rancidity of the fat is reduced. This layer is called “barrier layer”.

 

What are the traditional methods followed for preservation of methods?

• Salting
• Drying
• Marinating
• Fermentation
• Combination of the above methods

Though the methods are traditional, these are widely adopted in developing and under developed countries.

What are all the advantages of traditional methods of preservation?

• Cheapest methods of preservation
• No expensive technology
• Can be employed in both small scale and large scale
• Used for the preservation of low value fishes
• Make the product available in the remote area as well as throughout the year
• Operational skill is not required
• No need of technically qualified people

Which is the traditional method of preservation practiced widely?
Simple sun drying is the widely practiced traditional method of fish preservation.

What is the principle of preservation by sun drying?
Preservation by sun drying was achieved by lowering of water content in the fish, thereby retarding the activity of bacteria and fungi. The heat was able to destroy the bacteria to a certain extent.

 

 

What is basis of preservation by salting?
When salt introduced into the flesh in sufficient quantity, it delays the activity of bacteria or even inactivates them and reduce enzymatic action by reducing the water activity.

What are all the Advantages of salting?

• Low cost of production
• Easiness and compatible with other preservation methods such as drying and smoking
• Does not require any special equipment
• Finished product does not required any special storage facility
• Any type of fish, preferably, low and medium fat fishes
• Product has good shelf life
• Nutritionally comparable with other preservation methods

 

What is the principle of preservation by drying?
The moisture content and water activity is reduced and hence microorganisms cannot grow and multiply to spoil the fish. It can be seen that microbiological growth is completely arrested below a water activity level of 0.6 whereas certain other reactions that cause food spoilage continue. Lipid oxidation in fact increases at very low water activity.

What are all the advantages?

• Dried and dehydrated foods are more concentrated
• Less costly to produce
• Processing equipment is limited
• Storage area required is less
• Distribution costs are minimum
• Preserving the fish for a long time

 

What is hurdle technology?
Hurdle technology (also called combined methods, combined processes, combination preservation, combination techniques or barrier technology) advocates the deliberate combination of existing and novel preservation techniques in order to establish a series of preservative factors (hurdles) that any microorganisms should not be able to overcome.

Why hurdle technology should be used in fish preservation?
Spoilage and poisoning of fish and fishery products by micro-organisms is a problem that is not yet under adequate control, despite the range of preservation techniques available (e.g. freezing, blanching, pasteurizing and canning). In fact, the current Consumer demand for more natural and fresh-like foods, which urges food manufacturers to use Only mild preservation techniques (e.g. refrigeration, modified-atmosphere packaging and biopreservation), make the preservation even greater difficult task.