1. Handling of fresh fish; sanitation in
processing plants. Principles of low
temperature preservations
Lecture - 3
2. HANDLING OF FRESH FISH; SANITATION IN PROCESSING
PLANTS. PRINCIPLES OF LOW TEMPERATURE
PRESERVATIONS
Fish Handling: When fish are captured or harvested for commercial
purposes, it needed some pre-processing activities along with lowering
of temperature, so that fishes can be move to the next part of the
marketing chain in a fresh and undamaged condition. If fish is caught
by a fishing vessel need proper handling so they can be stored safely
until the boat lands the fish on shore. Typical handling processes are
transferring the catch from the fishing gear (such as a trawl net,
fishing line) to the fishing vessel holding the catch before further
handling
Sorting and grading
Bleeding, gutting and washing
Chilling
Storing the chilled fish
Unloading, or landing the fish when the fishing vessel returns to port
3. The number and order in which these operations are undertaken varies
with the
Fish species
Type of fishing gear used to catch it
How large the fishing vessel is and how long it is at sea
Nature of the market it is supplying
Catch processing operations can be manual or automated. The
equipment and procedures in modern industrial fisheries are designed to
reduce the rough handling of fish, heavy manual lifting and unsuitable
working positions which might result in injuries.
A. Fish harvesting: Care of fish begins as soon as they are caught in
the net or hook. The fishes killed or died without
much struggle helps in keeping quality for longer
period. The big fishes may be killed by giving a
stunning blow on the head.
4. B. Washing, sorting and grading of fish:
After hauling of fishes, they should be washed to make them free of
dirt, sand and other extraneous matter.
The non-edible and damaged fishes are picked up from the lot and
kept separately to be used for fish meal production, manure or for any
other purposes.
The rest of the good fish should be handled carefully to avoid crushing
under toot or by the gathering implements like shovels etc.
To maintain a complete hygiene, the surfaces of boat-decks, fish
holds, fish baskets, tubs, trucks and shovels etc. with which the fish
come into contact should be hygienically maintained.
Mud, slime, blood etc. which happen to get deposited on the boat,
baskets, tubs, trucks, shovels etc. during the fishing, handling and
transporting stages provide ideal situations for bacterial multiplication.
Hence all the surfaces which come in contact with the fish should be
free from these contaminating materials.
5. Clean and disinfect these surfaces thoroughly by scrubbing and
through application of detergents like teepol, washing soda, soap,
or trisodium hypochlorite solution containing 100 parts per
million of available chlorine.
However phenolic detergents are not suitable for this purpose
because they leave their smell on the cleaned surfaces containers and
on the fish.
The final washing is done with clean water to remove the
excess of chlorine. In short, whatever materials that come into contact
with the fresh fish including the ice used for short term preservation,
should be cleaned and disinfected thoroughly.
6. Fish is a highly perishable product and it gets spoiled by the action
of bacteria, enzymes and biochemical degradation. However most
of the spoilage of fish occurs due to the bacterial action.
Removal of visceral organs and the gills from the big fishes helps in
maintain quality of fish because these two organs are prime site of
bacteria and enzymes. However this is not needed in the case of the
small fishes as the gills and visceral contents are less.
Removal of the visceral organs should be done under hygienic
conditions. Otherwise this itself will become a source of
contamination to all other fishes and the instruments, containers and
the whole operational area.
Evisceration and de-gilling is done before transportation, canning,
salting and drying. In the case of prawns, removal of head serves the
same purpose as evisceration and de-gilling.
7. C. Handling of wet fish: As soon fish is caught/landed preserve it by
chilling in ice this method is called wet chilling.
Chilling is a process by which temperature of the fish is lowered to a
point near freezing but not below it by means of heat
withdrawal.
Super chilling: Storage of fish at temperatures between 0⁰C and -4⁰C
is called super chilling or partial freezing.
Freezing point for different fish species varies between –0.6 and –
2.2oC and depends on the concentration of the cell fluids.
It is usually taken as equal to –1oC.
Fish and fishery products processed in this way are called as chilled
products.
8. Chilling: After the dirt and visceral matter removal, temperature is the
next most important factor responsible for the spoilage of the fish.
Higher the temperature, faster the rate of spoilage. The retention of the
edible quality of fish increases with decreased in temperature. This is
clearly shown in table as given here.
Temperature effect on the number of days of storage for fish fit for
consumption
Sl. No Temperature oC Duration of storage
1 30 8 to 10 hrs By Icing
2 20 1 day “ “
3 15 2 days “ “
4 10 3 days “ “
5 5 4.5 days “ “
6 0 10 days “ “
7 -5 15-20 days By freez.
8 -20 300 days other tech.
9. Temperature can be maintained up to 0oC by icing. Beyond 0oC we
have to go for deep freezing techniques.
Fish can be stored tor more than 300 days if we use dry ice (-78°) and
liquid nitrogen (-196°C).
Chilling at sea: Sea water contains 3-3.5% salt. At 3.5% salt, freezing
point dips at about -2oC.
10. Refrigerated seawater: Refrigerated seawater (RSW) and chilled
seawater (CSW) has been cooled to just below 0°C. In some cases,
a brine of about the same salinity as seawater is used. There is no
clear distinction between the two terms; RSW is generally used when
a mechanical refrigeration unit cools the water and CSW is more
often used when ice is added for cooling.
Recommended ratio of fish to refrigerated sea water is between 3:1
and 4:1.
RSW systems have been used for sardine, salmon, halibut, menhaden,
shrimp, mackerel, herring, blue whiting and many other species.
11. Advantages of RSW:
(1) Greater speed of cooling
(2) Reduced pressure on the fish
(3) Lower holding temperature possible
(4) Quicker handling of large quantities of fish with little delay or
labour involvement
(5) In some cases, an extended storage time
Disadvantages: These include excessive uptake of salt, uptake of
water by species with a low fat content, loss of
protein, problems with anaerobic spoilage bacteria,
and modification of characteristics of fish
traditionally used as quality indicators, e.g.
"bleaching" of gills, dulling of skin, and leaching of
soluble end products of spoilage changes.
12. D. Icing: Icing is most common in India. Ice blocks are easily available
in most part of the country. The crushed ice is placed at the
bottom of the container and then a layer of fish is placed.
Over this layer another layer of crushed ice is spread and a
second layer of fish is placed. Thus layers of crushed ice and
fishes are placed in the container. The top is covered with
another layer of ice. Mixing salt with crushed ice increases
the rate of cooling. The iced fish can be transported to other
places where it is to be marketed. The ice melts slowly and
leaching takes place. In that case re-icing is needed after a
day or two.
For temporarily storage refrigerated sea water is also used. For
preserving fish in refrigerated sea water, clear and filtered sea water is
poured into the container in which fish is already kept. Fill the
container till all the fish is immersed in the sea water. The container is
refrigerated. This method is very rarely used in India.
13. Ice and refrigerated sea water preservation methods have their own
merits and demerits.
Cooling is faster in refrigerated sea water as the fish get full contact
with the sea water. Such contact is not possible in the case of crushed
ice.
Fish does not get pressed or crushed as it may happen in the case of
fish stored in crushed ice. There is greater control of the temperature
in the case of refrigerated sea water and we can bring down the
temperature up to -1°C while in the case of ice storage; the
temperature hardly reaches 1.5 to 2°C.
14. Storing fish in the refrigerated sea water requires less labour
compared to the icing.
In the refrigerated sea water storage there is accumulation of bacteria
on the surface of the fish whereas in the ice storage due to the
continuous leaching caused by melting of ice the bacteria are
continuously washed down.
Due to leaching, certain amount of nutritive compounds are also
washed down.
In general the fish preserved in refrigerated sea water is found to be
better in quality than the fish preserved in ice.
15. Icing of Fish
Icing is the most prevalent method of preserving fish and involves
packing of fish in crushed ice alternatively in insulated boxes. Ideal
ratio of fish to ice is 1:1 (w/w). By this, the temperature of the fish is
lowered to near 1 to 2°C in about 2-3 hrs (the melting of the ice needs
80 calories of heat/g and this heat is removed from the fish in contact
with ice and hence, the fish get cooled).
Lowering of temperature brings about
Arrest of almost all enzymatic changes,
Killing of about 50-60% of the mesophilic bacteria and
Slowing down of the activities and growth of all other
bacteria, which are cold-loving (psychrophilic) and cold-tolerant
(psychrotrophic).
As a combined effect of all these three factors, the spoilage of fish is
delayed to a considerable length of time in ice.
During iced storage of fish, there is an initial drop of bacterial count
due to the death of the cold sensitive mesophiles.
16. Icing of Fish
Qualitatively, there is a selection of bacterial flora during iced
storage of fish. Irrespective of the composition of the initial flora, the
Pseudomonas/ Alteromonas group emerges as the predominant group
of bacteria at the time of spoilage.
This is because most of the psychrotrophic bacteria capable of
spoilage belong to these genera.
In tropical fishes, psychrotrophs, which are the actual spoilers
during iced storage. Psychrotrophs have a shorter generation time
compared with psychrophiles.
17. iv) Convenience. Ice has a number of practical properties that makes its
use advantageous. They are:
a) It is a potable cooling method. It can be easily stored, transported
and used. Depending on the type of ice, it can be distributed
uniformly around fish.
b) Raw material to produce ice is widely available. Although clean,
pure water is becoming increasingly difficult to find, it is still
possible to consider it a widely available raw material and it should
be properly treated, e.g., chlorination.
c) Ice can be a relatively cheap method of preserving fish. This is
particularly true if ice is properly produced (avoiding wastage of
energy at ice plant level), stored (to avoid losses) and utilized
properly (not wasted).
d) Ice is a safe food grade substance. If produced properly utilizing
drinking water, ice is a safe food substance and does not cause any
harm either to consumers or those handling it. Ice should be handled
as food.
18. v) Extended shelf life.
The overall reason for icing fish is to extend shelf life fresh fish
of in a relatively simple way as compared to storage of un-iced fish at
ambient temperatures above 0oC. Extension of shelf life means
producing safe fresh fish of acceptable quality.
