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
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,
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
- 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
- The smell of raw and cooked
seafood is a reliable guide to quality because spoiled seafood has a
strong offensive smell. - Fresh food has a pleasant, mild
flavour which differs from group to group (fish, molluscs, and crustaceans) and from species to species. - 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.
- Fresh food has a pleasant, mild
flavour which differs from group to group (fish, molluscs, and crustaceans) and from species to species. - The taste of fresh seafood is a
good guide to freshness because flavour gradually disappears during storage. - 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.
- The flesh of fish is juicy and
tender and only rarely is it tough. - 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.
- 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.
- 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.
- 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).
- 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.
- 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.
- 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.
- 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.
- 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
- Cleaning and splitting
- Salting (bath or injection of liquid brine or dry salt mixture)
- Hanging
- Smoking
- Cooling
- 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:
- the higher the fat content, the slower the salt uptake;
- the thicker the fish, the slower the penetration of salt to the
centre; - the fresher the fish, the more slowly salt will be taken up;
- 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:
- Relative humidity (RH) of the air
- Air velocity
- Air temperature
- Surface area of the fish
- The nature of the fish: a high fat content in the fish retards
the rate of drying. - The thickness of the fish: the thicker the fish, the further
the water in the middle layers has to travel to reach the surface. - Temperature of the fish: diffusion of water from the deeper
layers to the surface is greater at higher temperatures. - The water content
Dehydration
procedure
- Wash the fish thoroughly.
- Open the belly cavity and the visceral organs.
- Rinse the fish in running water. Drain.
- Mix 10% brine solution (1 part salt to 9 parts water).
- Soak the fish in a 10% brine solution of salt for 30 to 40
minutes. - Drain the fish and wash thoroughly.
- Place the salted fish in woven bamboo racks to dry under the
sun or solar dryer for 2 to 3 days. - Let cool, then place in clean boxes or baskets or wrap them in
wax paper. - 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:
- Placing the material to be preserved onto the shelves when it
is still unfrozen. - 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. - The machine turns on the vacuum pump to force air out of the
chamber, lowering the atmospheric pressure below .06 ATM. - 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. - 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. - 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:
- The
contents of the cans must be commercially sterilized. - 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. - 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 |
1824 | Salmon canning started at |
1843 | Mackerel canning |
1844 | Oyster canning |
1864 | Fish canning industries |
1867 | Dunbars first canned |
1870 | Canning of sardine became |
1917 | Canning of tuna started |
1959 | Export of canned shrimps |
1970’s | Several shrimp canning |
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 30oC
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 70oC 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.
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