Of Fish-Process And Its Prevention
Singh, Mohd Danish and Amita Saxena
of Fishery Biology, College of Fisheries,
University of Agriculture and Technology, Pantnagar, Uttrakhand,
The foods are usually classified as less perishable, moderately
perishable and highly perishable in order to understand their
perishable nature. Cereals, nuts and grains are included in less
perishable and more stable category, vegetables as moderately
perishable and seafood's as highly perishable food items. Seafood's
are less stable because of their high moisture content and
availability of nutrients for the growth of microorganisms. Ambient
temperature plays a crucial role to alter the stability of a product.
Highly perishable foods like seafood's have low tolerance to
ambient temperature, while moderately perishable items like fruits
and vegetables have increased tolerance and non perishable items are
factors of spoilage
Spoilage and freshness are the two qualities that have to be clearly
defined. A fresh product is defined as the one whose original
characters remain unchanged. Spoilage therefore is the indicative of
post harvest change. This change may be graded as the change from
absolute freshness to limits of acceptability to unacceptability.
Spoilage is usually accompanied by change in physical
characteristics. Change in colour, odour, texture, colour of eyes,
color of gills and softness of the muscle are some of the
characteristics observed in spoiled fish. Spoilage is caused by the
action of enzymes, bacteria and chemicals present in the fish. In
addition, the following factors contribute to spoilage of fish.
is highly nutritive. It is tasty because of its constituents. The
main components of fish are water, protein and fat. The spoilage of
fish is a complicated process brought about by actions of enzymes,
bacteria and chemical constituents. The spoilage process starts
immediately after the death of fish. The process involves three
invasion and putrefaction
Rigor mortis is a physical effect on the muscle tissue of fish caused
by chemical changes following the death. In live fish, its movements
are controlled by chemical signals which cause the eythmic
contraction (stiffing) and relaxation of the muscles. This produces
swimming action. After the death, the normal circulatory system
breaks down and chemical signals leak into the muscle causing them to
stiffen. This process is known as Rigor Mortis. In other words, in
live fish the glycogen present in the muscle is converted to carbon
dioxide and water after supply of oxygen to the cells. After the
death of fish, the blood circulation stops and the supply of oxygen
is prevented. The enzymes present in the muscle convert glycogen into
lactic acid. The pH of the fish muscle falls. The formation of the
lactic acid continues till the supply of glycogen is completely used
the completion of rigor mortis, muscle stiffness gradually decreases
accompanied by increase in pH, ending up in softening of muscle. This
is followed by breakdown of proteins by enzymes. This process is
called as autolysis.
autolysis can be described as an internal breakdown of the structure
of the protein and fats due to a complex series of reactions by
enzymes. Autolysis of protein starts immediately after rigor and
creates favorable conditions for the growth of bacteria.
important action of the enzymes is that it affects the flavor of
fish. The components responsible for the taste and flavor of the fish
are changed by the enzymatic action. An example is the progressive,
degradation of ATP to AMP and Hypoxanthine. Hypoxanthine is produced
by the breakdown of ATP which is a main component of fish muscle
nucleotide. The accumulation of Hypoxanthine imparts a bitter taste
in the fish muscle accompanied by loss of fresh fish flavor. Thus the
estimation of Hypoxanthine content in fish indicates the degree of
action also causes decomposition in the fish known as belly bursting.
The belly bursting is caused by the action of digestive enzymes
present in the gut of the fish.
black spot formation in shrimps is also caused by the action of the
enzymes on the amino acid. The black colour is due to the formation
of Melanin (Black Pigment
) by the action of enzyme tyrosinase on
tyrosin present in the shrimps. Black spots present a poor appearance
and therefore, are not acceptable.
of the Bacteria
freshly caught fish will be almost free from bacteria but the surface
slime, gills and intestine may contain considerable load of bacteria.
When the fish is dead, these bacteria start attacking the flesh
causing spoilage and produce undesirable compounds. The nature and
type of bacteria present in a fish depends upon the water from where
it is caught and methods used for handling of the fish after its
catch. The important changes brought out by the action of the
bacteria in fish are as follows.
Reduction of TMAO to TMA
Marine fish contains a small percentage of odourless TMAO which
is reduced to an offensive smelling TMA by the action of bacteria.
Breakdown of Amino Acids and formation of Primary Amines
bacterial action of amino acids present in the fish muscle leads to
formation of primary amines. Examples are formation of histamine from
histidine, arginine from glutamic acid etc. This bacterial action may
cause food poisoning in extreme cases.
Breakdown in Urea
high concentration of urea in the flesh of some fishes is degraded to
ammonia by the microorganisms. The formation of ammonia is
accompanied by an offensive odour.
most common chemical action which causes spoilage is the oxidative
rancidity in fatty fishes. The levels of peroxide value and free
fatty acid content both a measure of oxidative rancidity are
considered an index of quality of fat fishes.
spoilage in fish is accompanied by the change in physical
characteristic. Changes in color, texture, odour, color of eyes,
color of gills, softness of muscle, belly bursting are some of the
characteristics of spoiled fish.
spoilage of fish is caused by enzymatic, bacterial and chemical
action. The activity of organism can be controlled, reduced or even
retarded by proper handling and immediate lowering of the
temperature. The chilling of the fish immediately after catch and
holding the fish at 0 oC by proper icing will reduce the
spoilage. In case of shrimps, removing head immediately after catch
will reduce the rate of spoilage. In the case of big fishes,
beheading and eviscerating will reduce the enzymatic actions which
spoilage is reduced or prevented in a number of ways like drying,
salting, chilling, canning and freezing. Chilling is a means of short
term preservation of seafoods achieved by the reduction in
temperature using ice. Freezing is the most satisfactory method
currently available for a long term preservation of seafood. It is,
in fact by far the best way of preventing fish from spoilage, since
fish continues to remain in almost the same natural conditions even
after freezing. It is effective for retaining flavour, colour and
nutritive value of seafoods. Freezing is a process by which the water
in the fish muscle is crystallized into ice. The crystallization will
be complete at -40 oC.
freezing, the fish must be stored at a temperature maintained
constantly at -18 oC or below. Fluctuation in this
temperature will cause spoilage of products. If there is a wide
variation in the temperature recrystallisation takes place.
Dehydration is another important reaction of a physical nature caused
by the evaporation of ice due to differences in vapour pressure over
the product surface and in the air of the store room. Loss of the
moisture by evaporation of ice causes the product surface to dry
resulting in dull appearance and even discolouration in some cases.
The evaporated water eventually condenses and freezes on the cooling
surfaces of the store room and the transfer of moisture from the
product will be continuous. Proper glazing and packaging eliminates
of material for freezing is an important process requiring
intelligent skill, extreme precaution and careful operations. The
spoilage process can be controlled to a large extent by observing
good manufacturing practices. The most important steps involved in
the good manufacturing practices are:-
of raw material, in process material and finished products.
handling of material.
of good quality ice and water.
of high standards of personnel hygiene and cleanliness.
adherence to cleaning schedule of utensils, tables, equipments,
of entry of insects, rodents and birds into handling and processing
of correct cold stoeage temperature.
temperature and hygiene play important role in the processing of
seafoods. Speedy work, proper icing and cleanliness in processing
operations, go a long way in reducing spoilage.
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Gopakumar,K.2000. Enzymes and Enzyme products as Quality Indices.
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J.Agric and Food Chemistry. 32: 314-319.
Lima Dos Santos, C.A.M, James, D and Teutscher, F.1984. Guidelines
for chilled fish storage experiments. FAO Fisheries Technical paper,
No 210. FAO,Rome.
Putro, S.1986. Better on board handling of oil sardines in the Bali
Strait using chilled sea water.Infofish Marketing Digest. 86(1):
Seafood — Fish — Crustacea
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