Preservation and processing of fish

How long can fish or meat be
kept?
 Fresh fish will spoil very quickly. Once the fish
has been caught, spoilage progresses rapidly. In
the areas of high temperature, fish will spoil
within 12 hours, which make them
unconsumable.
 Thus the marketing of fish becomes difficult task
because the fish should reach the consumer
before the quality of fish reduces.

When has fish or meat gone bad?
 Spoilage is the deterioration of food which make
its taste and smell bad ( sour or rotten) and
makes it a carrier of disease germs.
 In fish and meat the most important kinds of
spoilage are:
 1. autolytic spoilage caused by enzymes
 2 .microbiological spoilage caused by bacteria
 3 .fat oxidation
 Breakdown of proteins occur fastly in fish flesh
as compared to other meat although the
composition is same.

1) Enzymic changes
 Enzymes are proteins which assist biological
reactions, e.g. the conversion of certain organic
substances into different ones. When fish or
animals are killed, the enzymes inside them are still
intact.
 Those enzymes start breaking down components
into smaller parts and cause release of toxic
substances, which affects smell, taste and makes
the flesh soften.
 Formation of TMA (trimethylamine), DMA and NH3
by decomposition causing deterioration producing
bad smell.
 PH increases from normal 6.4 to 7.8

2) Bacterial spoilage
 Bacteria are the micro organisms invisible to
naked eye, break down the wastes and bodies
of dead organisms.
 Under favorable conditions and due to
enzymatic changes microbiological spoilage
starts quickly in fresh and non-acidic products
such as fish and meat.
 They breakdown the cellular part or matrix of
flesh by secreting some enzymes.

3) Fats Oxidation
 With fatty fish or meat, chemical reactions can
take place between the fat and oxygen in the air
(oxidation reactions).
 By exposing these products for a long time to air,
e.g. during drying and smoking, the product
acquires a rancid smell and taste.

 Preservation is the processing of food so that
they can be stored for a longer time.
 Preserved food is not healthy as fresh food
because it decreases the nutrition value of food.
 Before preservation, fish is processed and
washed with clean water to remove the mucus
and other such materials which can cause
problem in preservation.

Methods of preservation
 Fish can be preserved through
 Drying
 Freezing
 Salting
 Smoking
 Canning

1 1)---DRYING
 Drying is the oldest way of preserving foods.
 When sufficient water is removed from a
product, micro-organisms can no longer grow.
 The simplest and cheapest method is to dry the
product in the open air (with or without sun).
 They are hanged on ropes for two or three days
with regular turning over of fishes in order to
expose every part to the sun.

2)--FREEZING
 In this method the fishes are kept in wooden
boxes from all sides or in freezing cells with a
temperature of -20 to -30 degree centigrade.
 The low temperature prevents bacterial action
and autolysis.
 The fish can be freezed for not more than 6
months after that quality of fish reduces.

3) SALTING
 Salt is the preservative agent used to
lengthen the shelf life of fish and fishery
products. This is used in almost all methods
of preservation except in icing, refrigeration
and freezing.

PROCESS
 In this type of preservation salt is rubbed on all
sides of fish including the visceral cavity.
 On thicker parts of fish, scars are made by
knife and then salt is rubbed there for deep
penetration.
 These fishes are kept in cemented or metallic
tubs in layers , each layer having a thick coating
of salt on both sides.
 After about three days these fishes are
removed and dried in sun for 2 to 3 days. This
common salt inhibits the growth of micro
organisms and makes the enzymes inactive.

4)--SMOKING
 Raw fish and meat can also be preserved by
smoking. The preserving effect of the smoke is
a result of drying (withdrawal of moisture) of the
product during the smoking.
 The smoke particles, after being absorbed by
the product, inhibit bacterial growth on the
surface of the product.


 Preparation
 Fish can be smoked whole, cleaned, split or
filleted, depending on local preferences and the
desired final product.
 Meat must be cut into strips 5 cm wide and 1
cm thick before being smoked. An important fact
is that the greater the surface area of the meat
or fish, the greater the amount of smoke
particles which can be absorbed during smoking
and the better the product can dry.
 Applying of salt solution and sun drying before
smoking gives better result.

19
5) Basics of Canning
 Food is placed in a jar and
heated to a temperature
that destroys targeted
microorganisms.
 Heat also inactivates
enzymes that cause
spoilage.
 Air is driven from the jar
during heating. As the jar
cools a vacuum seal is
formed.
Can It!

Steps to canning fish
1. Start with fresh and healthy fish.
Remove the head, tail and bones of
large fish and wash thoroughly with
cold water.
2. Cut into desired size pieces.
3. The fish is also salted and smoked to
remove blood and water from flesh,
this also denatures the protein which
makes the fish stay firm and not
shrink after canning.
4. Fill hot, clean, pint or half-pint jar,
leaving 1-inch headspace.
 Seal jar and place in canner.
 Process for 100 minutes at 240
degrees at11 pounds pressure with a
dial gauge.

Continue….
 Turn off heat at the end of processing.
 Let pressure drop to 0 psig naturally.
 Wait 2 minutes after pressure drops.
 Open the canner.
 Remove the jars and cool it for 24 hours
undisturbed.

Preservation and processing of fish

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