Processing of fish. pptx

Fish preservation is a very important
aspect of the fisheries. Normally the
fish farms or other fish capturing
sites are located far off from the
market place and there is chance of
fish decomposition and the
uncertainties of their sale in market.

•In some regions, more fish is caught at
times than can be consumed. When the
fishes are caught in numbers, greater
than the amount of consumption, their
preservation becomes a necessity for
their future use.

Fish is a rapidly perishable food item
•Preservation keeps the surplus fish in
good condition for later consumption.
Again, fishermen sometimes cannot
return to their villages promptly with
fresh fish they have caught, and it will be
of value to them to know how to
preserve their catch by simple means.

•Preservation methods maintain the
quality of fish for a longer period of
time.
•However, while achieving
preservation, care has to be taken to
ensure that the wholesomeness,
taste, texture, physical appearance
etc. are also maintained to the
maximum possible extend.

Some of the important reasons for preserving foods are
1. To take care of the excess
produce. 2. Reaches areas where
the food item is not available 3.
Makes transportation and
storage of foods easier 4.
Preserving Foods at Home.

•Preservation and processing therefore
become a very important part of
commercial fisheries. It is done in such a
manner that the fishes remain fresh for
a long time, with a minimum loss of
flavour, taste, odour, nutritive value and
the digestibility of their flesh.

•Before thinking to preserve, one
needs to consider the freshness
of the fish as well as the other
ingredients. This is an important
factor as this affects the quality
of the foods to be preserved

Freshness is usually judged in the trade
entirely by appearance, odour and
texture of the raw fish. Since assessment
depends upon the senses, these factors
are known as sensory or organoleptic.
The most important things to look for the
freshness of fish are:

•The general appearance of the fish
including that of the eyes, gills, surface
slime and scales and the firmness or
softness of the flesh. The odour of the
gills and belly cavity; The appearance,
particularly the presence and absence of
discolouration along the underside, of
the backbone.

Fish being the most perishable of human foods;
starts spoiling the moment they are taken out of
water and die. Temperature being a very important
factor accelerating the process of spoilage, in a
tropical country like India the ambient
temperatures is very conducive for causing quick
spoilage in fish. The spoilage reaction proceeds at
a very rapid rate. It is well known that the rate of
spoilage of fish at 2.5◦c is twice as fast as that at
1.1◦c.

• The spoilage cannot be stopped completely. The
best that can be done is to allow it down by
means of some refrigeration techniques, the
simplest of which is addition of ice.
Types Of Ice
Ordinary ice is manufactured is different forms
viz, block ice, flake ice, cube ice, tube ice, plate
ice and soft ice, the last one resembling frost.

Block Ice
Block Ice is conventionally manufactured in the
block form, which is crushed to smaller pieces for
icing. Crushed ice has a large surface area, which
will ensure rapid cooling than the large blocks. For
making the block ice, water in ice cans is placed
in tanks of refrigerated sodium or calcium chloride
solution. Ice blocks are formed within 12 - 24
hours. The ice blocks are formed in few hours in a
rapid block ice plant.

Flake Ice
Ice with smooth contours and in the
shape of very thin flakes is called flake
ice. It has an area of 100 - 1000 mm2
and a thickness of 2 - 3 mm. Flake ice
has a very high area per unit mass and
can cover large quantity of fish for a
given weight when compared to
crushed block ice.

Plate Ice Plate ice is made by spraying water on to the surface of
vertical hollow plates through which a refrigerant passes. A flat
sheet of ice will be formed on the surface of the plate

Tube Ice is made as hollow cylinder of about 50 mm with a wall
thickness of 10 to 12 mm.

Liquid ice or Flow ice Liquid ice or flow ice looks like jelly.
Soft Ice Soft ice is made by freezing a weak
brine or seawater in a drum provided with
refrigerated walls. The crystals of fresh water ice
forms slurry in the brine as temperature falls and
it is pumped into a storage tank.
The principle involved in icing is that the ice absorbs its
latent heat of melting from its surroundings ( here, from
fishes ).

Some of the advantages of ordinary ice for cooling fish are
1. it is non toxic and hence can be brought into intimate contact with
fish
2. Cooling is rapid and the coldness is retained in direct contact.
3. When ice melts, the water washes away the slime and bacteria from
the surface of fish.
4. Ice has favorable inherent thermostatic properties
5. Ice has high relative humidity and hence retards desiccation of the
fish.
6. It is cheep and efficient.

Preservation Of Fish Onboard The Vessel
Preservation of the fish by ice is the cheapest
and reasonably efficient method practiced
onboard the vessel. Generally fish can be stored
in ice and kept in good condition for a period of 3-
15 days depending on the species. Fatty fish like
oil sardine has a short shelf life in ice. The fish
easily get rancid due to oxidation of unsaturated
fatty acids. Also the belly portion gets softened
owing to the action of enzymes and bacteria. For
minimizing the belly bursting in oil sardines, either
a dip in brine or sprinkling of salt before icing is
recommended.

Evisceration And Removal Of Gills
All large fishes like sharks, rays and other
fishes may be eviscerated and preserved
onboard. Bleeding is usually done by cutting
the throat and allows the fish to remain in
cold water for about half an hour. Gutting also
can be done simultaneously. Gills also may
be removed. As the gills and viscera
harbour innumerable bacteria which can
bring about spoilage after death, removal
of gills and guts will enhance the keeping

However the removal of viscera shall be complete
and a through washing after operation is very
important or otherwise the exposed belly portion
is liable to be contaminated. Similarly if the fish
is not bled during ice storage the blood will clot
and become dark brown affecting the appearance
of the meat. The removal of gills and viscera as
well as bleeding of the fish has to be done
separately. After this operation the fish has to be
washed thoroughly before it is packed in ice or
preserved otherwise.

As fish become unfit for human consumption in
about 8-12 hours after they are taken out of water,
it is imperative to cool them down with crushed ice
as early as possible after they are caught in order
to retain this freshness for the maximum length of
time. The fish pass into rigor mortise almost
immediately after death, during which they attain a
rigid structure. When once the rigor is resolved,
the fish become soft and bacterial proliferation
starts. Icing has to be done before this stage set
in, i.e. when the fish is still stiff.

• Method of icing plays a very important role in
bringing about the cooling. The ice should come
in close contact with the fish. The best method of
doing this is by putting ice and fish in alternate
layers in the container, the bottom and top layers
also being ice. Total height of the fish - ice mixture
so stored should not exceed 1 meter as other
wise the fish in the lower layers get crushed due
to the weight from above. The thicker the layers
of fish, the more the time required to cool down
their centers.

Quality of ice used shall be sufficient to bring
down the temperature of the fish and keep
the fish at low temperature for sufficient time.
Generally icing is done at 1:1 level (. ie. 1
kg ice for every kg fish.) and ice is
replenished at intervals to keep the
temperature from rising. For icing, crushed
ice having more surface area per unit mass
and cover more fish enabling rapid removal of
heat from fish may be used.

Approximate periods of shelf life of some of
the important marine fishes in ice storage are
seer fish 10 days, tuna 7 days, brackish water
prawn 7 days, mackerel 14 days, oil sardine
14 days and jewfish 14 days. From the point
of view of efficiency of cooling, flake ice is to
be preferred to crushed block ice as it makes
better contact with the fish with out bruising
their bodies by the sharp corners of the block
ice.

Prawns without any discoloration of
the shell or meat are usually packed
as headless frozen which fetch the
maximum price. Development of
discoloration of any sort reduces its
value as a raw material. Hence
utmost care is required in handling
and storage of prawns.

•One of the early symptoms of spoilage
in prawns is the loosening of the head
which affect the quality of the whole raw
frozen prawns. Special care especially
treatment with meta bisulphate and
storage in finally divided ice will help a
long way suitable for processing as head
on.

Removal of the head before storage in ice
is of value in reducing the percentage
incidence of black spots. Prevention of free
entry of air into the material and avoidance of
contamination with copper will also reduce
black spot development. Chemical treatments
are also useful. Treatment for 2 minutes in
a 0.25% solution of sodium or potassium
meta bisulphate before storage in ice
greatly reduce black spot development.

PRESERVATION IN REFRIGERATED SEA WATER
Even though refrigerated sea water has been
widely employed for preservation of fish in many
overseas countries, the method is practically
unknown in India. The principle employed here
is to hold the fish in natural or artificial sea
water cooled to -1◦c. It appears to be more
suitable for preserving fresh fish onboard the
fishing vessels

In the early stage of development of this process, cooling
of the brine or sea water was effected by adding blocks
of ice. This method has the disadvantage of diluting the
brine, besides, the problem involved in carrying large
quantities of ice required for a whole fishing trip and also
labour and space requirements. This was solved by
employing mechanical refrigeration for cooling the brine,
the temperature being maintained slightly above the
freezing point of the fish which otherwise undergo a
process of slow freezing with accompanying problems
like denaturation of the proteins.

It consists essentially of an insulated tank separated into
two compartments, the larger one to hold the fish and the
smaller one for cooling coils through which a refrigerant
is circulated at the required temperature by means of a
compressor system. Cooled brine from the smaller tank
is pumped to the bottom of the storage tank by a pump,
P1, where it rises uniformly through a perforated partition
through the stored fish. The brine is drawn out just below
the top surface into the cooling tank by pump P2 for
further cooling. Thus the same sea water is circulated
around the fish with sufficient cooling to maintain the
desired temperature in the fish.

The fishes are thoroughly cleaned and placed
in the storage tank. It is preferable to
eviscerate larger fishes and clean them well
before storage in the sea water tanks. All the
fish should remain well under the surface of
the sea water. Cooling of the brine prior to the
introduction of the fish ensures quicker
chilling. The temperature of the sea water is
thermostatically controlled at 0 C or -3◦c.

RSW VERSUS ICE STORAGE
•Both the preservation systems have
their own merits and demerits. While
much more efficient and rapid
cooling is achieved in RSW due to
thorough and intimate contact of the
cooling medium with the fish,
crushed ice pieces do not make such
perfect contact.

Fish held in RSW have buoyancies almost equal to
their weights and to what ever height the tanks may
be filled, the fish don’t get pressed or crushed, where
as in ice storage if the depth of fish and ice stored in
one container exceeds about half to 1m, the bottom
layers of fish get crushed and more often bruised by
the sharp corners of the ice pieces. There is better
control of temperature is RSW storage (-1◦c) where as in
ice storage it is difficult to bring the temperature even
below 1.5-2◦c

One of the disadvantages of RSW
storage is that the medium
accumulates heavy bacterial loads
especially if the surface of fish is not
cleaned before storage in the tank.
This problem has to be solved by
frequent changes of the sea water.

Belly Burn
In the case of some fishes like tuna and salmon
stored in RSW in whole condition, softening
followed by bursting of the belly walls occurs after
some days especially if the fish had been feeding
heavily at the time of capture. This phenomenon
called belly burn has been attributed to
autolysis, ie, decomposition caused by the
enzymes present in the intestine and muscle of
the fish. In-corporation of 1.5 ppm of
Chlorotetracycline in the RSW used for storage
delays the belly burn.

PRESERVATION IN CHILLED SEAWATER ( C S W )
Another method of storing fish is in seawater
or dilute brine made up to the concentration
of sea water by mixing it with ice generally
referred to as chilled sea water. This is very
simple method. There are also instances
where it is advantageous to combine RSW
and CSW systems where some cooling is
provided by refrigeration and some by ice.

• In RSW system it is necessary to circulate the water by
pumping to ensure even mixing and cooling. This may
sometimes be done with a CSW system also, but
pumping is generally not necessary in fishing
vessel, as the motion of the vessel itself will provide
adequate mixing.
• Another advantage of CSW is that freezing of fish
which is a possibility in RSW doesn’t occur here.
• Freezing is also likely to render the eating quality of fish
poor.
• In RSW and CSW storage, the recommended ratio of
fish to water is between 3:1 and 4:1.

In conventional CSW system, there may be
problems associated with the uniformity of
temperature in the tanks. Ice also tends to form
icebergs on the surface which can obstruct the
circulation and reduce the space. The
CHAMPAGNE CSW system overcomes these
problems. In this system, air is pumped along the
bottom of the tanks which ensure the constant
movement of the ice/water/fish mixture around the
tank and ensures high heat transfer, uniform
temperature and better fish quality.

D R Y I N G A N D D E H Y D R A T I O N
Drying is one of the oldest known methods of
preservation of food. Though the technology of
food preservation and processing has undergone
revolutionary changes over the years and several
new products processed employing diverse
techniques, have made their firm presence in the
market, drying still continuous to be the most
widely used method for preservation of several
foods including fish. It is also considered the least
expensive method of food preservation.

Water is essential for the activity of all living
organisms including microbes. Reduction in
the water content or its complete removal
by drying will retard or totally stop all
microbial and autolytic activities, thus
preventing spoilage and resulting in
preservation. About 20 % of
the fish caught annually is used for curing
in India.

Water Activity
Microorganisms need water in an available
form to grow in food products. The control
of the moisture content in foods is one of
the oldest exploited preservation strategies.
Food microbiologists generally describe the
water requirement of microorganisms in
terms of water activity (aw) of the food.

Advantages of dried foods
1.Dried and dehydrated foods are highly
concentrated foods compared to any other
preserved form of foods.
2.Drying reduces the microbial activity and thus
reduces the spoilage of foods due to microbial
activity.
3.With reduced water content, enzymatic and many
chemical processes are retarded.

1.Dried foods are less expensive to produce.
2.There is no involvement of complicated
machinery and equipment for processing and
packaging.
3.They are stable at most ambient temperatures.
4.Transportation and distribution costs are
minimum.
•

Sun Drying
Drying involves removal of water from a body in
our contest fish. Traditionally fish used to be dried
under sun and the term drying has come to imply
drying under the sun. This is the simplest method
of drying fish. The fishes dried in this way are
small, lean ones, which are available in plenty
during the glut season. Sun drying is carried out in
the open air using the solar energy to evaporate the
water in the fish. The evaporated water is carried
away by the natural air currents.

They are usually spread out on the seashore
as whole with little preprocessing. Sometimes
they are given a washing in the seawater.
Drying takes place usually by the removal of
moisture from the surface and later from the
interior of the fish. Depending on the relative
humidity, temperature, air velocity, the
removal of moisture takes place continuously.

Fish is also conventionally dried on coir mats,
cement platforms, bamboo mats and jute sacks.
Often this sort of drying gives a product, which is
contaminated with sand, and other foreign
matters. The fish dried on cement platform gets
partially dried due to the excessive heat. It
becomes necessary that the fish is turned over
often to ensure a uniform dried material.

The advisable method for drying fish is
drying them on rack. Here the fish is dried
on a raised platform above the ground. This
can be made by tying old webbing (net) to
poles made of locally available materials like
casuarinas, bamboo etc. which are fixed at
regular intervals. Here the main advantages
are that there is a circulation of air from
both top and bottom. There is no
contamination of the product; hence a
quality product is assured.

The efficiency of this process and the quality of the
product remain at the mercy of the nature and there fore
the product suffers from serious disadvantages,
some of which are
• Dependence on weather; the operations can be
carried out only when bright sunlight is available.
• Long duration of drying; under unfavorable
conditions of weather, drying may take several
days to complete.
• There is no control over the operating parameters.

• Possibility of contamination with dust
and sand.
• Possibility of infestation with insects,
their eggs and larvae.
• Poor quality of the product.
• Short shelf life.

An important achievement in drying is the
development of artificial dryers where
the important operational parameters like
temperature, relative humidity and
velocity of air can be controlled. This has
lead to dehydration which refers to a
process of drying under controlled
operational parameters like
temperature, air velocity and relative
humidity.

•In order to control these parameters,
drying has necessarily to be carried out
in an enclosed atmosphere. Most of the
disadvantages encountered in sun drying
can more or less be overcome and a product
of desired quality and reasonable shelf life
can be obtained by dehydration. However,
the terms drying and dehydration are being
used now without much specificity.

Preparation of the material
Before drying, the fish is often subjected to
different pre-process operations which are mainly
dependent on the size and nature of the fish and
also the end product desired. Conventionally, very
small and thin fishes like Anchovilla are dried
whole without salting. Small fishes like sole, small
croakers, Anchovilla etc are salted whole and
dried. However gutting and cleaning before
salting will reduce spoilage and improve the
quality.

Splitting open, or cutting into pieces before
salting is necessary in the case of bigger fishes.
In the case of very big catfish, shark, rays etc.
they are split open and deep cuts are made in
the exposed flesh before salting. This will
increase the area of exposed flesh for greater
contact with salt, permit easy penetration of salt
and increase the surface area for evaporation of
moisture and thus bringing about a reduction in
the time required for drying.

Fish may be dried without salting or after
salting. It is better that the fish is
immersed in brine rather than in dry salt,
so that the required concentration of salt
in fish flesh is achieved in a shorter time.
It is also desirable to employ saturated
brine to enable easier uptake of salt by the
fish flesh.

Mechanical dryers 1. C a b i n e t D r y e r
This is a simple batch operation model dryer used
for relatively small scale operations. A typical
cabinet drier may consists of an insulated or non-
insulated framed structure. Materials to be dried
are uniformly spread in trays and placed on
permanent supports provided in the dryer. A fan
located inside the dryer will blow air from a heat
source which pass across or through the material
loaded in trays.

2. K i l n D r y e r
Kiln dryer is also a batch dryer. A typical drying kiln
will consist of a two stored building. The floor of
the upper store is of slotted on which the material
can be spreaded. This serves as drying room. The
burners or furnas producing hot gas is located in
the lower floor. The hot gas passes through the
product by natural conduction and often forced
circulation with the help of a fan also may
become necessary. The material has to be turned
and stirred frequently to ensure uniform drying.

T u n n e l D r y e r
Tunnel dryers are most commonly used for drying
fish. These are made in the form of long tunnels 10
-15 meter long. Trolleys loaded with trays
containing fishes are moved at a pre-determined
schedule through the tunnel. Hot air is blown over
the material across the trays. For drying fish using
the tunnel dryers, the production cycles are so
planned that when a trolley of fresh fish leaves the
dryer at one end, a fresh trolley of fish to be dried
is introduced at the other end. Therefore, this is a
continuous operation and not a batch type.

S p r a y D r y e r
Spray dryers are generally used for drying foods which
are in the form of liquids or suspensions. In principle, a
food in a liquid or paste form is atomized and dispersed
as minute droplets which are suspended in a stream of
hot air in a chamber where it gets rapidly dried. The
dry particles suspended in the air stream, flow into
separation equipments where they are separated from
the air, collected and packaged. In the application of
spray drying in products, it is limited to products like fish
protein hydrolysates and fish powders.

V a c u u m S h e l f D r y e r
Vacuum shelf dryer consist of a vacuum tight
chamber of heavy construction with access door
and outlet for gases and vapours. Hollow
shelves through which the heating medium is
circulated are fitted inside the chamber. The
material to be dried is spread in fairly thin
layers in metal trays which rest on these
shelves. Alternately the material can be
spread directly on the shelves.

Heating is done by circulating hot air stream
or any other suitable heating medium.
Vacuum will be drawn in the chamber through
the vapour outlet and drying will proceed
under vacuum. It is considered an expensive
process. However, it is quite suitable for
drying fatty fishes where the probability of fat
oxidation and rancidity in the product can be
minimized.

S o l a r D r y e r s
Utilizing the solar radiation for solar powered
dryers has attracted considerable interest
because of the absence of any energy cost
and possibility of producing a dry fish in good
hygienic condition even when the relative
humidity is high. Energy of the sun is
collected and concentrated to produce
elevated temperatures suitable for drying
several commodities including fish.

One of the simplest forms of dryers to use solar energy
for drying fish is the solar tent dryer. This is working on
the principle that a black surface absorbs sun’s energy
more effectively than any light coloured surface. The air
thus heated is allowed to pass through the fish and
escape out through a vent in the top, simultaneously
admitting fresh air inside through a vent provided at the
bottom of the tent. Here the air temperature is known to
raise the levels of 60◦c or more in tropical climates.
This will adversely affect the nutritional as well as
physical properties of fish and is considered as a
disadvantage.

• However, compared to normal sun drying, solar drying
has the following advantages.
• No energy cost
• Very low equipment cost
• Shorter drying periods
• No contamination from dust and insects
• Produces hygienic product with low moisture content.

Dried Bombay-duck
The Bombay-duck holds a pride of place in
the long established artisanal sector of the
northwest and northeast coasts of India. A
good or poor harvest of Bombay- duck
exercise direct influence upon the livelihood
of men and women engaged in this labour
intensive sector in the maritime states of
Maharashtra and Gujarat.

It is an important fish for domestic use and
also a valuable export item in dried or
laminated form. Fresh extracts from Bombay-
duck is believed to have considerable
medicinal properties. The fishery is supported
by a single species, Harpadon nehereus,
popularly known as Bombay-duck, The water
content of this fish is 58 to 92 % and hence,
sun drying is the common method of
preservation.

Non laminated Bombay duck
Sundrying of Bombay duck on scaffolds is the
traditional method of preservation of the fish on
the Maharashtra and the Gujarat coasts. The fish
after being washed in sea water is locked in pairs
at the jaws and hung on ropes tied between poles
to be dried in the natural breeze and heat.
Complete drying of the product requires 3-5 days
depending on the weather conditions. After 3-4
days the fish is removed from the scaffolds and
further dried by spreading on palmyra mats.

Laminated Bombay ducks
Fresh fish are washed in water
containing 1-2 per cent salt and 0.05-
0.1 per cent citric acid. The fish
flattened by longitudinal cuts to
remove entrails and vertebral column
and spread over wire mesh trays on
bamboo platforms and dried in sun till
the moisture content is brought down
to 10%. The laminated fish is pressed
individually by passing through a
roller press. The individual pieces are
trimmed into uniform size and shape.

Effect Of Drying On The Quality Of Fish
1) Shrinkage
1. Case hardening
Water in the fish contains dissolved salts, proteins and other organic
matters. Water moving to the surface of the fish carries all these, while
that leaving the fish surface is only pure water depositing the dissolved
substances on the surface. If the temperature of drying air is high and its
relative humidity is low, this will form a dry impervious layer on the
surface. This condition is referred to as case hardening and the final
product becoming brittle. It can be controlled by maintaining
sufficiently high relative (RH) humidity in the drying atmosphere
and also controlling the temperature of drying.

Denaturation Of Protein And Toughening Of Texture
As the drying progresses, concentration of
dissolved material in the body water
increases. Reduced evaporation due to case
hardening will result in increase of
temperature of the fish muscle. These bring
about denaturation of protein and the texture
becomes tough.

Spoilage Of Fish During Drying And Storage
Dried and drying fish are susceptible to many type of spoilage
which can affect the quality and shelf life.
A. Molds
Molds can grow in dried fishes if the moisture content is
high and high RH above 75% prevails in the storage.
Molds are likely to grow if the temperature is 30-35◦c.
With the onset of molds, the surface moisture may
increase and the fish may become susceptible to other
type of spoilage.

B. Insect infestation
• Salted dried fish are often infested with
insects. Adult flies are attracted to the dried
fish and their larvae feed on it. Infestation
with flies can be reduced by maintaining
hygienic condition in fish handling and
processing premises.

C. Rancidity
Fatty fish particularly are prone to oxidation
and development of consequent rancid
flavour. Though some degree of rancid
flavour may be acceptable in dried fish,
excessive rancidity will be objectionable.
Rancidity will be controlled to some extent
with air tight packaging of dried fish.

Salting is a traditional method of
preservation of fish practiced as such or
in combination with drying and smoking
and is considered a practice as old as
drying. Salt curing, though is an important
method of preservation by itself with or
without subsequent drying, is one of the
most widely practiced method of fish
preservation throughout the world.

When introduced in sufficient quantities in the fish
flesh, salt can delay the activity of bacteria or even
inactivate them by reducing the water activity. This
forms the basis of preservation by salting.
•

The advantages of salt curing over many other
methods of processing are
1.Does not require elaborate equipments.
2.Capital out lay is small.
3.Methods are simple and the processing
is comparatively inexpensive.

1.Unlike other sophisticated methods of processing,
curing can be applied for preservation of any type of
fish.
2.The finished products do not require any special
storage facility.
3.The products have reasonably good shelf life.
4.Nutritionally, the products are comparable to fish
processed employing most other methods.

When fish is mixed with salt or kept in
salt solution, some water is removed
from the flesh depending on the
amount of salt used dry or in solution.
Lose of water from fish flesh reduces its
water activity. During salting process salt
enters the fish flesh and water in fish
moves out due to osmosis.

• Presence of salt up to 4 -10% in the fish flesh is
known to prevent the action of most spoilage
bacteria as well as autolytic decomposition. . In
general growth of many putrefactive bacteria is
considered to be controlled at salt concentration over
5%.
• When the concentration of salt is 20% or more in
the flesh the decomposition process in the fish
proceeds only very slowly.

With reference to the sensitivity towards the salt
bacteria can be divided into three groups.
• 1 Halophobic or salt sensitive:- These include most
of the pathogen and putrefactive types. These
organisms can not grow in a medium where the salt
concentration is higher than 6%. Eg: Pseudomonas
and Achromobacter sp.
• 2. Halotolerent These consist of spore formers,
micrococci and some anaerobes particularly
Chlostridium botulinum. They can grow in
concentrations higher than 6% and even up to
saturation, although the rate of growth decreases with
increase in concentration of salt.

3. Halophylic These are salt loving organisms
which grow best in the presence of salt. Practically
the halophyles fail to grow in the absence of salt
and the optimum growth occurs in salt
concentration higher than 20%. Bacteria causing
red and pink in salted fish are the most important
in this group. These are aerobes with optimum
range of temperature grow in the range 15-50◦c.
Most of them fail to grow below 10◦c. They are not
pathogenic.

Salting Methods
Dry salting
• Dry salting is the simplest method of curing fish.
Dressed fish are kept intimately mixed with
crystalline salt in containers and salt may even be
rubbed into the gill cavity and the scores made in
the fish flesh. A layer of salt is spread on the
bottom of the tub and a layer of fish is placed on
it. Salt and fish are spread in alternate layers, the
proportion of salt increasing upwards

•A solution of salt will be formed in the
water exuded from the fish and the fish
will remain in the brine. The fish may
float in the brine formed. In order to
ensure proper salting of all the fish,
weights are often used to keep them
immersed in the brine. Fish will be
allowed to remain in brine for 2-3 days
after which it can be taken out and dried.

Kench salting
•It is essentially a method of dry salting
except that the self-brine formed is
allowed to drain off. Split fish after rolling
up in crystalline salt or rubbing salt is
stacked in layers within a thin layer of
salt. The self brine formed is allowed to
drain away.

Brine salting
In this method of salting, fish is kept immersed in
brine of desired concentration for the required
time. This is usually done as a step preliminary to
smoking and canning. A strong cure is not possible
in brine salting because the brine will become
progressively diluted with the water released from
the fish. If a strong cure is needed, the brine
should be replaced with a strong one after the
initial brine becomes diluted.

4 Mixed salting
•Salting process is slow when the fish is
large in size or is oily. As a result it takes
long time for the self brine to form and
cover the fish. This may cause the fish in
top layers to spoil before salt is picked
up by them. An advantageous method of
salting employed in such cases is mixed
salting, also called pickle curing.

•In mixed salting particularly used for median
size fatty fish like herring, the fish is first
mixed with dry salt and then packed in water
tight containers with salt sprinkled between
each layer. It is then topped with saturated
brine. Mixed salting has the advantage that
the fishes are completely surrounded by
brine right from the beginning and thus
increases the salting process.

Types Of Salted Fish
• Based on the quantity of salt used, salted fish can be divided into 3
categories - light salted, medium salted and heavily salted.
• Salting aims at saturating the water in the fish flesh wholly or
partially with common salt. For light salted fish 16-20 parts of salt /
100 parts of fish is used. The resultant products will contain about
20-30% salt on dry weight basis. For medium salted fish, 20-28 parts
by weight of salt is used for every 100 parts fish and the resultant
product will contain 30-40% salt on dry wt basis. Heavily salted fish
will have above 20-28 parts by wt of salt for every 100 parts fish.

Spoilage Of Salted Fish
• Bacteria exhibit different degrees of tolerance towards
salt. Most of the bacteria usually associated with fish
spoilage are HALOPHOBIC in nature and will not grow
when the salt conc. is in excess of 5%. However there
are other organisms which are halophylic and can grow
in environments of high salt concentrations. In addition
to the action of bacteria, changes in the protein, fat, etc.
also will contribute to the spoilage of salted fish.

Pink or red
• It is a common type of spoilage associated with
salted fish manifesting mostly during storage in
warm weather conditions. The surface of the
fish becomes covered with a red slime that
gives of an unpleasant odour. This is brought
about by halophyles which need salt conc.
above 10% for their growth. The spoilage is
called pink or red because of the colour of the
colonies of the bacteria appearing on the fish
surface.

• The microorganisms responsible for this
phenomena are halophylic rods and cocci
originating from the salt used in the process,
particularly solar salt. They include Halobacterium
salinaria, Sarcina littoralis and Micrococcus rosens.
They are all aerobic organisms active only while in
contact with air. They are thermophiles with an
optimum temperature of growth of about 42◦c. They
will not grow at temperature below 10◦c.

•The flesh turns alkaline and becomes
inedible. This phenomenon can be
prevented by treatment with
formaldehyde or sulphur dioxide
vaporous or by dipping in a solution of
sodium metabisulphite. Treatment with
sodium and calcium salts of propionic
acid also effectively controls the
development of pink.

Moulds
•Moulds are often seen to grow on salted and
unsalted dried fish. Dun is a type of mold
development observed even in heavily
salted fish. This is characterized by the
appearance of coloured spots black, grey
or brown. This imparts an appearance as if
sprinkled with ground black pepper. The
small spots develop a root network into the
interior of the fish flesh.

• This is caused by a group of molds of which
Sporendonema epizoun is mostly identified with. It
has optimum growth at 10 -15% salt conc. 75% RH
and 25◦C. The mold activity itself may make the
surface moist and pave the way for the fish
becoming more susceptible to other types of
spoilage. The moulds can be easily removed in the
early stages. They will reappear rapidly. In case of
severe infection, dipping in 0.1% sorbic acid will give
some protection. Effective control may be achieved by
use of good quality salt, maintenance of low
temperature and humidity, well ventilated and dry
storage conditions.

Putrifactive spoilage
•If the salting process is very slow, it will take
long time for the salt to reach the center of the
fish and to saturate it. This can cause spoilage
in such regions. The flesh near the back bone
become tanned or reddened accompanied by
the development of putrid smell. Any pre-salting
operation which can accelerate the penetration
of salt into the interior of the flesh like gutting,
splitting etc. can prevent the development of this
phenomena.

Fragmentation
•Cured and dried fish often become brittle
and break during storage and
transportation. This is referred to as
fragmentation. Denaturation of protein
followed by the insects attack, use of spoiled
fish for processing etc are the reasons
ascribed to this.

•Smoking or smoke curing like drying and salt
curing is an ancient method of preservation
of fish. In the early methods of smoking,
heavily salted fish used to be smoked for
long durations, few weeks even and the
resultant products had long shelf life at
ambient temperatures owing to the high
salt concentration and long smoking and
drying periods which lower the water
activity considerably.

In course of time, the hard cures gave way to
milder products with less salt and lower duration
of smoking. Such a product however has only
short shelf life. These are more favoured and
relished because of their specific mild flavour
and are considered delicacies.
When fish is smoked, it is subjected to 4
basic treatments viz, brining, drying, smoking
and heat treatment.

•This type of preservation is effected either
by hot smoking or cold smoking. In hot
smoking, the temperature of smoke may rise
at times to above 100◦c while the flesh
reaches 60◦c and gets cooked. The heat
treatment also results in partial sterilization
though subsequent re-infection and spoilage
of the cooked flesh is still quite rapid. During
cold smoking, the temperature is not more
than above 60◦c and the fish is not even
partially cooked.

Formaldehyde, acids and phenols are the important
constituents of smoke involved in smoke curing of fish.
Among these, phenol constituents are supposed to be the
most effective in preserving fish.

MASMIN – is a smoked product of tuna at Lakshwadeep
Each tuna is cut into four fillets like pieces without
bones. These pieces will be slow boiled in a sea water-
fresh water mixture for about 6-7 hours. The cooked
pieces will be smoked on indigenous kilns for 2 days. The
cooked and smoked pieces will be sun dried for 8-10 days
until they acquire hard, wood like consistency. The
masmin will be packed in plastic bags and exported. The
masmin sector has good scope for quality improvement.

An innovative value added product
has been developed using a new
processing method by smoking and
drying skip jack tuna meat which is
similar to the commercially available
masmin flakes. Major ingredients
used for the product preparation are
skipjack tuna and salt.

•Minced tuna meat is mixed with salt and
liquid smoke, made into a paste and
stuffed inside a stainless steel mould after
which blocks are cooked and dried till the
moisture reaches below 15%. Using a
flaking machine masmin flakes are
produced and dried again to get the
product of moisture content below 10%.

Flakes are then packed in polyester/polythene laminated
pouches and stored at room temperature. Masmin flakes
prepared by improved method has superior biochemical
qualities compared to traditional masmin flakes. The
lower moisture of masmin flakes assures higher shelf life.
Nutritional profiles such as protein content and lysine
content are high. It shows higher levels of PUFA
especially EPA, DHA and can play a vital role in attracting
consumer health consciousness to this product.
•

Electrostatic Smoking
• A process of smoking developed and popular in
the Soviet Union is electrostatic smoking.
Smoking takes place as a result of the electro
kinetic properties of smoke in a high voltage
field of the order of 40 k w. or more. Salted
and rinsed fish is passed through a drying
chamber heated by infrared lamps positioned
on either side of the belt carrying fish. Fish is
heated for 3-4 minutes at 40-50◦c in the
chamber when they loose around 5% of its
weight.

They are then taken to the electro static
smoking oven over a conveyer. On either
side of the conveyer, are nichrome
electrodes suitability placed. The
electrodes are supplied with high voltage
current of 30-70 K W while smoke is
admitted to the bottom of the oven. For a
good smoked appearance of the fish, at
least 1mg of smoke substances must be
precipitated / cm2 of fish surface.

•This requirement is attained in lass
than 5 minutes in the oven. From the
smoking chamber, the fishes are
carried to the baking oven fitted with
sufficient number of coils. In 5-6
minutes in the baking oven, the
fishes are heated to about 30◦c and
loose 10-12% of moisture.

The advantages of the process include.
1.Considerable saving in time as the whole process takes
only around 20 minutes and consequent increased
output.
2.Reduction in the losses because of the short processing
time.
3.The process is continuous and carried out in a
mechanical equipment.

C U R I N G
• The traditional methods of processing fish by
salting, drying, smoking pickling etc. are collectively
known as ‘Curing.
• Though produced in coastal areas, cured fish is
usually consumed in the interior markets and hilly
areas.
• Curing is a process by which the fish is preserved by
sun drying, salting, pickling, smoking, artificial
drying etc. This can be done either by any single
method or a combination of these methods.

• In the current market situation both wet and dry
cured fishery products have commercial
importance. Different methods are generally
followed.
• Dry Curing 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.
• 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 salted in cement tanks
or 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 over put down 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 solution
to remove adhering salt and
drained. It is then dried in the sun
to required level of moisture. Yield
of the product by this method is
about 35-40%. This product has a
shelf life of 6-10 weeks.

Wet 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
Palmyra leaf baskets 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 sardines, mackerels, and ribbon
fishes etc. wherein the fat gets oxidized on
exposure to air during exposure to air. That is
why it is not dried. When immersed in the tank
there is no contact with outside air.

Mona curing
• Mona curing is similar to dry curing and generally applied
to medium size fishes like mackerel, otolithes, lactarius,
etc. The main deviation in this case is that the fish are not
split open but the gill and the intestines are pulled out
through the mouth and cleaned. Then salting is done and
cured in the cement tanks as described in the case of dry
curing. The advantage here is that the flesh does not get
exposed during salting and drying and hence takes up
comparatively less contamination with microbes and
extraneous matter. The final product also presents a better
appearance. The yield in this method is about 70 per cent
and the shelf life approximately 50 days.

Pit curing
• This is a very crude and primitive method of curing,
practiced mainly in Tamil Nadu, and is getting extinct
due to the poor quality of the product. The fish degilled
and eviscerated and salted at the ratio of 4:1 (salt to
fish) are filled in the pits made in the sands of the sea
shore. The pit is lined with palmarha leaves. After about
36 to 48 hours the pit is opened and the fish is packed
in bamboo baskets and transported to market. The shelf
life is approximately 20 days.
•

Columbo curing
• This obviously originated in Columbo and is
essentially a pickling process. Mostly medium sized
fishes are preserved by this method. The fishes are
cleaned thoroughly after they are degilled and
degutted. They are salted as in the dry curing. A
piece of Malabar Tamarind (Garcinia cambogea) is
placed in the cavity of each fish and staked in a
wooden barrel. When the barrel is full it is filled with
saturated brine and closed water tight and exported.
The yield is about 75 per cent and the shelf life is
more than six months.

Microbiological and Heavy Metal Standards of Dried
and Salted Products
• i) Total plate count, Max / gm 100000
• ii) E.coli, Max / g 20
• iii) Coagulasepositive, Staphylococci, Maxlg 100
• iv) Salmonella, per 25 g Absent
•

v) Heavy metals:
• a) Mercury,mgkg, Max 0.5
• b) Zinc, mg/kg, Max 50
• c) Copper, mg/kg, Max 10
• d) Arsenic,mg/kg, Max 1
• e) Lead,mg /kg, Max 1

Canning is a method of preservation
of foods in which spoilage is averted
by killing the microorganisms by
application of heat and prevention of
subsequent contamination, by
enclosing the material in a
hermetically sealed container.
Hermetic sealing literally means air tight
sealing.

•Unlike other common methods of
preservation, canning alters the nature
of the material significantly forming
almost new products because of the
various treatments the raw materials are
subjected to and the various additives
used in processing. Containers for
canned foods are normally made of tin
plate but aluminium and other
modification are now popular.

History
• All methods of preservation of foods perhaps with
the exception of irradiation can be considered
adaptation of natural process or their
modifications. Canning has the unique distinction
of being an invention. The history of development
of canning as an important method of
preservation of food dates back to the mid 1790s.
In 1795 the French Government, faced with the
problem of feeding the fighting forces announced
a price of 12,000 francs and fame to anyone
inventing a useful method of food preservation.

• In 1809, Nicholas Appert, a French confectioner
won this price for his invention when he found
that foods remained safe for long periods if
heated in a sealed container. Appert called his
method of food preservation as appertisation.
Neither he nor the scientists of this period could
give a convincing explanation for the apparent
success of this process. It was in the 1880s, a
logical explanation for this could be provided
when Louis Pasture reported that it is a
microscopic vegetation that grew and spoiled
foods under unfavorable conditions.

Advantages of canning over other methods of
preservation
1.Canned foods offer consumer safety
2.Canned foods can be stored at room temperature
for long periods.
3.Canned foods are cooked foods and hence
instantly available for consumption with little or no
further preparation for the table.

1.Canned foods are concentrated
foods with no waste.
2.They are protected against re-
infection by microorganisms and
insects.
3.The process is applicable to a wide
range of products.

The different
steps involved in the conventional canning process are
the following.
1 ) Selection And Preparation Of Fish
• Thermal destruction of bacteria being the principle
involved in preservation of fish by canning, it is very
important that the fish used should have only a very low
bacterial load. Thermal destruction of bacteria follows a
logarithmic pattern. There fore higher the initial load of
bacteria, longer will be the time required for their
elimination. Longer exposure to high temperature will
impair the quality of the product. There fore, fresh
uncontaminated fishes should be used as the raw
material for canning

•Dressing ( evisceration) reduces the bulk of the
raw materials making its further handling
convenient.
•Nobbing Machines remove the head, tail and
viscera of sardine and sardine like fishes. There
are also automatic nobbing and packing
machines which automatically pack the nobbed
fish in to cans.
•

2 Salting / Blanching / Precooking
• Dressed fish is generally blanched in cold or hot brine or
pre cooked in steam. During blanching in brine, the fish
flesh takes up sufficient salt and its texture gets
improved. During heating as in hot blanching or cooking
in steam, the fish flesh releases around 15-30% of the
body water. If the fish is packed without removing this
much water before hand by some process, it will be
released in the can during heating processing. This will
render the product unattractive and form water-oil
emulsion or dilute the sauce depending on the canning
medium used.

The main functions of this process are,
1.Causes sufficient shrinkage of the fish to enable
adequate filling in the cans.
2.Imparts firm and proper texture to the meat
making its handling easy.
3.Clean the fish meat and reduce the bacterial
load.

1.Inhibits enzymatic reactions and maintains
nutritive value by retarding browning reactions.
2.Sets the natural colour of the product.
3.Expels the respiratory gases from the tissues,
thus helping to improve the vacuum in the can
and
4.Removes the raw flavour of fish.

3 Can Filling
• The blanched material is filled in clean cans.
Weight filled will depend on the specific
requirement with respect to the size of the can. It
is then covered with a liquid medium like hot
brine, oil or sauce. The liquid medium is a
constituent of the product and helps in improving
its taste, texture and flavour. It also facilitates
proper heat penetration in the product during heat
processing. Other additives like flavouring agents,
vegetables etc. may be added with a view to
improve the flavour, presentation etc.

• Double refined deodorized vegetable oil is the principle
filling medium used in fish cans. Tomato sauce is an
important additive in canned sardine, mackeral, oyster etc.
• The cans are filled such that a uniform head space of 6-9
mm is available above the contents. Can ends may bulge if
the head space is too little. This even causes uneven
sterilization. Too high head space also causes problems
because too much air in the can will accelerate product
deterioration and container corrosion besides adversely
affecting the vacuum.
•

4 Clinching
•While seaming the cans using high speed
machines, there is a possibility of the
contents spilling over. To prevent this, the
can end is clinched to the can body.
Clinching involves the can end being
partially secured to the body by a single
seam keeping the lid sufficiently loose to
allow escape of air and water vapour during
exhausting.

5 Exhausting
• Exhausting is the step by which air from the head
space and the contents is removed prior to seaming
the can. It is an essential step because it
1.Minimize the strain on the can and seams due to
expansion of air during heat processing.
2.Removes oxygen which can other wise accelerate
internal corrosion of can and oxidation of fat and
vitamins

•Creates partial vacuum in the can. When
stored at higher than normal temperature or
at higher altitudes, the ends of the cans that
are not exhausted will expand and present a
blown appearance. During exhausting, the
air in the can is replaced by steam. On
cooling, the steam condenses creating a
vacuum. Vacuum will ensure that the can
ends remain concave or flat even during
storage at higher than normal temperatures
and at higher altitudes.

6 Can Coding
• It is a statutory requirement to stamp the can ends
with a cod denoting the contents, date of manufacture
and other details as demanded under the food laws.
This can help in identify the batch and impound such
cans if any problem arises during storage. Coding is
done in figures and letters using an embossing
machine Coding should not damage the lacquer or the
tin coating which will lead to corrosion of the can.

7 Can Seaming
•The object of seaming is to get an air tight
seal between the cover and the body of the
container, so that microorganisms cannot
gain entry into the can. A double seam may
be defined as that part of the can formed by
joining the body and end components, the hooks
of which interlock and form a strong
mechanical structure. The can ends are attached
to the body using a double seaming machine.
The finished double seam consists of five
thickness of the metal.

Cross-section of a double seam away from the side seam

• Cans are seamed immediately after exhausting or along
with exhausting as in vacuum seaming.
• A good quality tin plate and an efficient can closing
machine and adequate sealing compound combined to
produce a strong hermetic double seam. The double
seam formed is always examined with reference to
standard measurements. The sealed cans are also
subjected to the pressure testing for checking the
perfection of the seams.

8 Can Washing
• Cans leaving the seaming machine may have
pieces of fish, sauce or oil adhering to the
surface. These can contaminate the retort, clog it
and become sources of contamination of
subsequent batches of can. Fish pieces sticking
to the can surface when removed later after
retorting may result in pealing away of the surface
lacquer, thus exposing a potential area for
corrosion.

•Surface contamination also may
prevent the label properly sticking to
the surface. There fore the cans are
washed before retorting in a hot
detergent solution like 1.5% sodium
phosphate at about 80◦c. The
washed cans are further rinsed in hot
water to remove any detergent
residue.

9 Processing / Sterilization
• The sealed cans are heated for a predetermined time - temperature
schedule in saturated steam. Thermal processing should take care
of the following aspects.
1. Consumer safety.
2. Ensuring non spoilage under ordinary conditions of storage and
distribution
3. Proper cooking of the product
4. Retention of organoleptic characteristics
•

• Complete sterility is not the aim of heat
processing because such a condition will affect
the wholesomeness of the product and even may
render the product organoleptically unacceptable.
The heat treatment should be such that it is
sufficient to kill or inhibit microorganisms
causing spoilage without over cooking the
product. Bacteria, spore forming or non
sporers, can be present in canned foods and
may not spoil the contents under the normal
conditions of storage.

So long as the product is free from pathogens
and otherwise good, it can be considered
hygienically acceptable. This has given rise to
the concept of commercial sterility which is a
condition achieved by the application of heat
where the food is rendered free from viable
microorganisms having public health
significance as well as microorganisms of non
health significance capable of reproducing in
food under the normal non refrigerated
conditions of storage and distribution.

•This implies that the
recommended process
doesn’t kill all
microorganisms, some spores
of thermophilic organisms
may remain and hence the
food is not bacteriological
sterile.

• The important consideration in canned fish is
preventing the growth of Clostridium
botulinum, a food poisoning bacteria that can
produce a highly lethal toxin under anaerobic
condition. A reduction in the population of
Clostridium botulinum by a factor of 1012 is
considered essential in canned fish. The process
can be considered successful if only one in
10,000 processed cans runs the risk of spoilage.
•

•Heat processing is carried out in retort. As a
counter check for the processing
temperature, there should be a provision in
the retort to read the temperature directly
using a thermometer in addition to the
pressure gauge. Different types of retorts
(autoclave) are used for heat processing of
canned foods. These include still retorts,
agitating type retorts, continuous retorts,
hydrostatic retorts etc. The still retort is the
oldest type and is still most commonly in

Still retorts are of two types, horizontal and vertical. The main difference
between the horizontal and vertical retort is that the former has its door at
the end where as the later has its door at the top.

• After loading the cans into the retort, steam is
admitted into it. After flushing out all the air in the
retort and after closing the drain and steam exit
valves, steam pressure is increased to attain the
operating pressure (15 PSI) and temperature (
121.1 C) and the retort is maintained for the
required time. The pressure and hence the retort
temperature is controlled either automatically or
manually. However, sole reliance must not be
bestowed on the gauge pressure. There should
always be a provision to read the retort
temperature directly using a calibrated

10. Cooling
• At the end of heat processing, the cans are cooled as
rapidly as possible to about 35◦c. Even after shutting of
steam supply, the temperature at the center of the can
will register a slight increase and the product will get
over cooked. In order to prevent this over cooking, it
is essential that the contents are cooled
immediately at the end of heat processing. Rapid
cooling will also prevent germination of any
remaining non pathogenic thermophilic spores in
their optimum temperature range.

•Cans should be cooled to an
average temperature of 35◦c only
and not below that, so that sufficient
heat is retained by the product to
evaporate water on the canned
surface and make it dry. Any water
retained on the canned surface may
lead to its external rusting.

11. Labelling
Cans are labelled to identify
their contents. Some canners
use printed cans. Can code on
the labels instead of embossing
on can ends is also in use.

12. Storage And Distribution
•Cans are usually stored for short periods
say 1-3 months before marketing. This
will help the contents to mature, ensure
equitable distribution of salt and other
additives like spices and also stabilize
taste and flavour. This also provides a
counter check on the soundness of cans
because any leak in the cans will show
up by this time.

•The temperature of storage is directly
related to the storage life of the canned
products. Considering 10◦c a highly
desirable storage temperature, it will
appear that increase of every 10◦c will
reduce the storage life by half of the
previous. Cans should not be stored at
freezing temperatures also as these will
result in an unsightly product on
opening.

•The storage facility should be well
ventilated and be free from moisture.
Presence of moisture in the atmosphere
will lead to its condensation on the can
surface and may lead to subsequent
corrosion of the can. Processed cans
should not be cased hot. Loss of heat by
radiation from the cans is slow and can
lead to a situation called stake burning
in the can.

•Spoilage or deterioration in quality or
accelerated corrosion caused by
retention of heat in stack of cans or
cartons for long periods is referred to
as stake burning. This may also
provide a favorable condition for the
growth of any surviving thermophylic
spores.

•Cans made of tinned steel plate are
especially used to store fish and meat
products. Sometimes it is better to use
glass; acid products, for example,
corrode cans and are therefore better
packed in glass. The shape and volume of
the vessels must be chosen according to
the quantity to be processed.

Canning of Fish
• Sardines are canned in many different ways. At the
cannery, the fishes are washed, their heads are
removed, eviscerated and the fish are cooked, either by
deep-frying or by steam-cooking, after which they are
dried. They are then packed in
either olive, sunflower or soybean oil, water, or in
a tomato, chilli or mustard sauce. Sardines are typically
tightly packed in a small can which is scored for easy
opening, either with a pull tab (similar to how
a beverage can is opened), or with a key attached to the
side of the can. Thus, it has the virtues of being an
easily portable, nonperishable, self-contained food.

Spoilage In Canned Fish
•Spoilage in canned food is quite unique.
Even a difficulty of the container like rusting
on the surface may be accounted as
spoilage, even though the contents may be
perfectly normal. Sometimes the can may
look perfectly normal externally, though the
contents might have become liquefied and
unfit for consumption which can be known
only on opening the can.

• Spoilage in canned foods may be mainly due to
microbial, chemical and physical means.
• Normal cans have concave or flat ends. A can
showing bulged ends is called a swell or blower. In
a hard swell the ends are permanently distended. A soft
swell is one in which the bulged end can be moved
back by mechanical pressure.

1. Microbial Spoilage
• Microbial spoilage takes place due to several
reasons, the important among them being under
processing, inadequate cooling and leak
infection.
• A canned food spoiling due to the survival and
growth of bacteria is under processed. If there is
gas production, a swell may result or the contents
may undergo acidification and liquefaction, but no
gas is produced.

•An important manifestation of under
processing is the flat sour spoilage. Flat
sour is a condition where the contents of the
can may be acidified and liquefied without
any gas production. Thermophilic spore
formers of the Bacillus sp. surviving thermal
processing are responsible for this type of
spoilage. Flat sour indicates the inadequacy
of the thermal processing, ie, under
processed.

2. Spoilage Producing Acid And Gas
•The biological spoilage evidenced by
production of acid and gas is caused by
thermophiles of the Clostridium sp. They
decompose protein with production of
toxic compounds like H2S, NH3, Indole,
skatol etc. The spoilage is indicated by
swelled containers and decomposed
foods.

• Thermal processing doesn’t envisage destruction
of all the thermophiles, since such a process will
often results in deterioration of the quality of the
food. The flat sour thermophiles multiply rapidly in
the temperature range 48-70◦c and if the
processed cans are not rapidly cooled to a
temperature below this range, may lead to
serious spoilage by thermophiles. The risk of flat
sour spoilage will persist if the cans cooled to
about 35◦c are staked immediately in large
blocks.

•A major threat to the safety of canned
food is spoilage arising from leakage
through seams which take place during
the cooling process after thermal
processing. The main source of
organisms is the cooling water.

3. Chemical Spoilage - Hydrogen Swell
•Cans which swell as a result of
hydrogen produced due to
internal corrosion of the cans is
known as hydrogen swell. The
bulging may range from flipping
to hard swell.

4. Physical Spoilage
•Normal cans have concave or flat ends.
A can showing bulged ends is called a
swell or blower. In a hard swell, the
ends are permanently distended. A soft
swell is one in which the bulged end
can be moved by thumb pressure, but
cannot be moved back to the normal
position.

• A can in which one end is bulged but can be forced
back to the normal position, where up on the
opposite end bulge is called a springer. A flipper is a
can of normal appearance, but on striking against a
solid object, one end flips out. Bulged can pass
through the stages of flipper, springer and soft swell
to the hard swell stage.
• Physically induced spoilage may arise from faulty
retort operation, under exhausting or overfilling.

Some Problems Commonly Associated With
Canned Fishery Product
1) Struvite Formation
• Some canned marine products such as brine packed
shrimp, crab or tuna shows the presence of some glass
like crystals particularly when the temperature of storage is
low. This takes place due to the formation of a chemical
compound magnesium ammonium phosphate hexahydrate
called struvite, Struvite is a harmless, colourless,
odourless, transparent chemical, however it has a glass
like structure and its presence will be mistaken for
fragmented glass and hence is considered objectionable in
the product

• Magnesium from the salt or sea water used in
various operations combines with ammonia
generated from the fish muscle protein during
heat processing and phosphates in the fish to
from struvite and the product gradually
crystallizes particularly when the cans are
cooled at a very slow rate after processing.

2. Sulphide Blackening
• Iron sulphide blackening is generally met within
canned shrimp, lobsters, crab etc. Though the fish
cans are coated with a sulphur resistant lacquer,
any imperfection in the lacquer coating or any
scratch on it during handling can expose tin. Tri
methyl amine present in marine fish will dissolve
the tin exposing iron. The sulphur containing
constituent released from the fish during thermal
processing will react with iron producing iron
sulphide which is black in colour.

Blue Discolouration
• Blue discoloration is usually associated with
canned crab meat. Meat from the parts of the
body having poor blood circulation such as legs,
claws etc show high incidence of blueing. The
copper in the hemocyanine in the crab
haemolymph reacts with the sulphur compound
liberated during thermal processing producing
blue copper sulphide.

•This phenomena becomes evident when the
copper in the meat is about 2 mg %. There
fore, the important method to prevent this,
consists in thoroughly bleeding the meat so
that copper reduced below this critical level.
Use of a chelating agent in the brine and
maintenance of proper acidity can control
the discoloration of the meat.

Honey Combing
•This is a phenomena observed in canned
tuna meat processed from stale raw material.
The meat in such cans resembles honey
comb. During steaming, the volume of meat
contract due to removal of water and
coagulation of protein. Coagulation starts in
the surface. The swelled gelatinous parts
solidify after cooling and exhibit honey
combed appearance.

Softening In Shrimp
• Canned shrimp often becomes very soft in cans.
The cause of this softening is the decomposition
of the protein to soluble non protein components,
which usually occurs in the raw materials when
freshness declines. To prevent this strictly, fresh
raw material should be used for processing and
high level of sanitation should be maintained in
the cannery.

Mush
•This phenomenon which is a flabby
condition is met within some species of
pilchards caught at the end of its
spawning season. It is caused by the
invasion of the parasitic protozoan
Chloromixum which decomposes the
fish meat during storage such that it
becomes entirely soft during canning.

Retort burn
•It is usually associated with canned shell
fish like clam, mussel or oyster. This is a
condition which develops when the filling
medium is not sufficient to cover the
solid food and the top is left dry. This can
be over come by using sufficient filling
medium to cover the solids in the can.

Retort Pouch
• A relatively recent approach in container
development for heat processed foods is flexible
thermoplastic films and aluminium foil laminate. A
retort pouch can be defined as a container which
when fully sealed will act as a hermetically sealed
container that can be heat processed at similar
temperature and pressure as for metal
containers. The retort pouch has the advantage of
metal cans and plastic boil-in-bag.

•The material used in retort pouch must also
provide superior barrier properties for a long
shelf life, seal integrity, toughness and
puncture resistance.
•The common pouch in use is a 3 ply pouch
which is a sandwich of thin guage aluminium
between two thermoplastic films. The outer
ply generally made of polyester provides
barrier properties and also mechanical
strength.

•The aluminium layer protects the
material against gas, light and water and
ensures adequate shelf life of the
contents. The inner polyolefin layer
which is generally polypropylene
provides the best heat sealing medium.
This is also an inert material and hence
doesn’t materially affect the contents.

F - VALUE
F-value originally called the sterilizing
value is used to denote the time in
minutes required to kill an organism in
a specific medium at 121.1◦c. i.e. its
thermal death time.

D value or Decimal Reduction Time or Death Rate
•D value is the time in minutes required to
reduce the number of survivors of bacteria to
one tenth of the original at a specified
temperature. D value is generally denoted with
a subscript of the temperature at which the
determination is carried out. For eg. D121
indicates the decimal reduction time
determined at 1210 C.

Thermal Death Time (TDT)
•TDT can be defined as the time in minutes
required to inactivate an arbitrarily chosen
number of spores of a given bacteria at a
specified temperature. Death is defined as
the failure of bacteria or spores to
reproduce when favourable conditions for
reproduction are provided.

Z Value
•Z value is the change in temperature necessary
to cause a tenfold change in the D value. The
value of Z for Clostridium botulinum is 100 C, by
which it is meant that for every 100C change in
the temperature, there is a tenfold change in its
death rate.

The Concept of Thermal Process Severity (Fo Value )
• The process depends on thermal process lethality, in
terms of exposure time to a specific high temperature,
sufficient to effectively eliminate the most dangerous
and heat resistant pathogens, particularly
Clostridium botulinum. Thermal processes are
calibrated in terms of the equivalent time the thermal
centre of the product, i.e. the point of the product in
the container most distant from the heat source or
cold spot, spends at 121.1°C, and this thermal process
lethality time is termed the F0 value.

Lacquering
•Certain food reacts with the metal of the
can resulting in corrosion of the metal
ultimately leading to its perforation.
Therefore, it is customary to coat the inside
of the container with a thin film of an inert
material to prevent the contact of the food
with the metal.

•This is done by lacquering the
tinplate before it is cut and made
in to cans. Two types of lacquers
are used in the food cans, the acid
resistant (AR) lacquer and the
sulphur resistant (SR) lacquer. SR
lacquers are used in fishery
products.

OTS CANS ( Open Top Sanitory )
• It is easy to open this can.
• The easy open ends made of aluminium which are popular
in beverage cans led to the development of such ends for
food cans including fish cans. The EOE have circular incision
which enables the whole central panel to be removed by
pulling an attached ring. Tinplate versions of EOE have now
been developed.

Tin Free Steel (TFS)
•TFS, an important alternate to
tinplate, has a steel base with a
chromium /chromium oxide
coating on the surface replacing
the tin in the conventional cans.

Pasteurization
•Pasteurization is another process which is
effected either by heat or high energy
irradiation. Here also a partial destruction of
bacteria in foods is effected. This reduction in
number of bacteria slows down the
development of spoilage flora and delays
spoilage if not prevents it altogether.
•

Double Seaming
•A double seam may be defined as that part
of the can formed by joining the body and
end components, the hooks of which
interlock and form a strong mechanical
structure. The can ends are attached to the
body using a double seaming machine. The
finished double seam consists of five
thickness of the metal.

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