Types of
Spoilage in Fish
Fish is a highly perishable
commodity. The Spoilage of fish being as soon as fish dies. In tropical
conditions, fish spoils quite rapidly, within a few hours of landing, if not
properly cooled. The spoilage rate of fish may be reduced by good handling
practices and effective temperature control from very beginning.
In raw fish,
spoilage takes place mainly due to three reason viz.,
1)
Enzymic
action
2)
Microbial
action
3)
Chemical
action
Enzymes and bacteria do not cause any
deteriorative changes in the living cell because of the natural defensive
mechanism. In dead fish, enzyme become involved in the autolytic changes and
bacteria can invade the fish muscle and proliferate there. The fish gut is rich
in proteolytic enzymes and in dead fish it digests the gut and belly region
making the fish very soft. Bacteria that are present on the surface, gills and
gut of the fish invade the dead fish, decompose the tissue and bring about
undesirable changes. Off odor and off flavor, slime, gas production,
discoloration and soft texture are the obvious signs of spoilage. Component
involved in spoilage process are protein, lipids, carbohydrates, nucleotides
and other non-protein nitrogen compounds. The rate of spoilage is temperature
dependent and lowering the temperature will reduce the rate of spoilage.
A) Autolytic spoilage (Enzymatic):-
Autolytic spoilage is responsible for early loss of quality of fresh
fish. The first enzymatic change in fish muscle is the gradual hydrolysis of
glycogen to lactic acid which is known as glycolysis.
1)
Glycolysis:-
After death, the blood circulation stops and the cells longer supplied
with oxygen and hence glycogen will not converted into the carbon dioxide and
water unlike in the case of living cells. In the postmortem period, glycolysis
proceeds via the anaerobic pathway where the end product is lactic acid. As the
lactic acid accumulates, the pH of the muscle falls. In fish, glycolysis will
continue until the supply of glycogen is completely used up. In general, fish
muscle contain relatively low amount of glycogen compared with mammalian muscle
and the final postmortem pH is consequently higher. This makes the fish meat more
susceptible to microbial attack.
2)
Flavor changes in fish ( Nucleotide
degradation):-
The most significant enzyme
deterioration is those that alter flavor. The nucleotide degradation in fish
muscle produces many flavor bearing compounds. These compounds are formed by
the splitting of ATP by series of dephosphorylation and deamination reaction.
Progressively it is hydrolyzed to ADP
(Adenosine diphosphate), AMP (Adenosine monophosphate) and to IMP (Inosine
monophosphate) and ammonia. At ambient temperature, ATP breakdown occurs
rapidly and IMP accumulates in the fish tissue. In fresh fish, the rate of IMP
is very high and it imparts a desirable sweet, meaty and characteristic flavor
to fish. As autolysis proceeds further, the level of IMP decreases and neutral
tasting Inosine or bitter tasting hypoxanthine accumulates in tissue. As a
result, fish becomes more insipid. Some of these compounds increases with time
and have been used as indices of fish freshness.
3)
Belly bursting:-
Enzymic spoilage causes belly
bursting in fish, especially during a period of high food intake. These fishes
will have a large content of digestive enzymes in the digestive tract. Such
fish will degrade quickly and spoil easily soon after they are caught. In the
dissolve gut components, bacteria proliferate and produce gases such as CO2, and H2. This gas production leads to belly bursting after short storage
period. Keeping the fish live for some time will retards this.
4)
Color changes in the fish:-
Color is an important factor in
seafood quality. Color change in seafood is caused by Enzymic or non-enzymic
action such as fat oxidation or by pigments. Color change in the seafood is an
indication of spoilage. The important discoloration in seafood caused by
enzymes or fat oxidation is illustrated below:
a. Black /blue discoloration
i)
Shrimp:-
The development of black spot in shrimp is due to the presence of an enzyme,
polyphenol oxidase (PPO). The black spot (melanin) is formed by the oxidative
reaction of tyrosinase on tyrosine. Different species of shrimp undergoes
postmortem discoloration to different extents. The pigment is formed on the
internal shell surfaces, or in advanced stages, on the underlying shrimp meat.
This makes the shrimp unattractive for marketing. The shrimp phenol oxidase
differs from that found in mussel or lobster in that it is not activated by
trypsin. Sulphite preservatives can be used to prevent black discoloration
resulting from phenolase reaction. Dipping shrimp in 0.2 – 0.5 % sodium
bisulphite for one minute is usually adopted in industrial practice.
ii)
Lobster:-
Black spot occurrence during icing
and frozen storage of lobster is serious problem which has resulted in
significant commercial losses. Tyrosinase activity was identified in the blood
with lesser amounts in other tissue. Discoloration at the butt of the tail,
black spot between the segments and other deteriorations are more pronounced in
moribund lobster. The tendency for blackening is also influenced by moulting
cycle.
iii)
Crab:-
Phenolase has been implicated in blue
– black coloration of crab. The enzyme is present in the blood. Various
additives have been shown to prevent blue discoloration (e.g. organic acid,
sodium bisulphite and EDTA). The haemocyanin induced blacking is also prominent
in crab and is non-enzymic.
b) Yellowing of fish flesh:-
Frozen storage of some fish may
result in yellowing of flesh below the skin. Freezing or other processes
disrupt chromatophores and release Carotenoids and their migrations to the
subcutaneous fat layer causes yellowing. Yellowing associated with lipid
oxidation and carbonyl –amine reaction is observed during frozen storage.
c)
Brown discoloration:-
Brown or yellow discoloration is
caused by the reaction of the protein or the amino acids with product of lipid
oxidation. Brown discoloration is observed in verity of processed products
including white pomfret, sardine, jack mackerel, salted shark, marine eel, etc.
Discoloration due to protein – lipid browning is greater in fatty fish than
lean fish.
B) Microbial spoilage:-
Fish spoilage is mainly due the
action of bacteria. Bacteria are present on the surface slime, skin, gills and
intestine of fish. In dead fish bacteria begin to invade the tissues causing
spoilage and production of undesirable compound. The type of bacteria on the
fish is very much depending on the microbial flora of the environment. However,
in the fish processing industries two types of micro-organism are of
concern.
1)
Saprophytic or spoilage type
bacteria:-
These organisms are responsible for
the spoilage of the fish. The important classes of spoilage organisms found in
tropical species are Pseudomonas,
Flavobacteria, Acinetobacter, Aeromonas and Moroxella. The spoilage
bacteria are characterized by their ability to produce H2S, reduce Trimethlyamine
oxide (TMAO) to Trimethlyamine (TMA) and convert urea to ammonia. Many volatile
sulphur compounds are also produced by Pseudomonas.
A quantitative measurement of these
compounds indicates the degree of spoilage. Fish flesh starts visibly to spoil
when bacterial level rises to above 107 organisms per gram.
The flesh losses its culinary
qualities like juiciness, firm texture, etc. changing it into a product that
becomes soft with loss of flavor, discoloration and off flavor. The major
deteriorative changes brought about by microorganisms in fish are the
following.
a) Formation of ammonia:-
Spoilage organisms convert many
nitrogen compounds into off smelling volatile bases. Non-protein compound
present in fish are good substrate for spoilage organisms. The free amino acid
pool in the muscle of fish is readily utilized by typical spoilage organism by
the process of deamination. This result in the formation ammonia which is the
primary compound produced during decomposition of fresh fish. Ammonia is the
major component in the total volatile nitrogen (TVN) fraction which often is
used as a quality indicator for fresh fish. Area present in elasmobranches like
shark and rays is degraded to ammonia by bacterial action. Thus, high level of
ammonia in these species is an indication of spoilage.
b) Formation of TMA:-
Marine fish is characterized by the
presence of an odorless compound called Trimethlyamine oxide (TMAO). Marine
flat fish and teleost contain low level of this compound (0.1-0.5%) while elasmobranches
(shark, rays, etc.) and gadoids contain very high level (1 to 1.5%). Spoilage bacteria convert this substance into foul
smelling Trimethlyamine (TMA). TMA is produced in fish muscle slowly at first
then at greater speed in fish stored at ambient temperature, in ice or in
refrigerated seawater. The fishy odor is produced when it reacts with fat.
c) Histamine formation:-
Microbial spoilage of fish produces
the toxin, histamine in certain fishes. Histamine poisoning or scombroid fish
poisoning is very frequent in many countries. Scombroid fishes and other dark
muscle fishes contain high level of free amino acid, histidine in their muscle.
During spoilage histidine is converted into histamine by bacteria. Over fifty
species including popular species such as Tuna, Bonito, Mackerel, Blue fish, Dolphin
fish (Mahi mahi), sardine, carangids,
herring, and anchovies were shown to be potential threat of histamine
poisoning. Histamine production increases with temperature and 370 C
is the optimum temperature for the microbial activity. Morganella morganii, Hafnia alvei, etc. are the main spoilage
organisms producing histamine. Low temperature storage, right from catch,
reduces histamine production.
d) Indole production:-
Conversion of tryptophan to indole is
another result of amino acid decomposition by bacteria. The FDA uses indole
level along with sensory evaluation for measurement of shrimp decomposition.
e) Other compounds formed during bacterial spoilage:-
A number of extractives are available
in fish for bacterial action such as free amino acids, sugars, peptides, creatine,
as well as lipid and proteins. Chemical examination of spoiling fish muscle as
shown that organoleptically the most important constituents are the volatile
sulphur compounds such as hydrogen sulphide (H2S), dimethyl sulphide(CH3)2S
and methylmercaptan (CH3SH). Ester of lower fatty acid such as
acetic, Propionic, butyric, hexaenoic acid etc. are also produced. Volatile
sulphur compounds influence the organoleptic characters, especially odors; in
spoiling fish. The overall qualitative chemical picture of spoiling fish in summarized
below:
|
Substrate
|
Compounds produced by bacterial action
|
|
Inosine
|
Hypoxanthine
|
|
Carbohydrate and
lactate
|
Acetic acid, CO2
& H20
|
|
Methionine & Cysteine
|
H2S, CH3SH
and (CH3)2S
|
|
Tryptophan
|
Indole
|
|
Glycine, Leucine
& Serine
|
Esters of acetic,
Propionic, butyric and hexaenoic acids
|
|
Trimethlyamine
oxide
|
Trimethlyamine
|
|
Urea
|
Ammonia
|
|
Lipids
|
Carbonyls
|
|
Proteins
|
Tyrosine, Indole,
skatole, putrescine, cadaverine
|
|
Histidine
|
Histamine
|
Some of the spoilage bacteria
proteolytic and undoubtedly contribute to the ammoniacal odor by producing
ammonia from the protein breakdown.
2)
Pathogenic bacteria:-
The pathogenic bacteria associated
with seafood’s are of two types:
a) Indigenous bacteria:-
They are widely distributed in the
aquatic environment. These pathogens occur in minimal numbers and are not a
serious problem in fresh fish. However, their growth and multiplication in
seafood is a serious problem and can cause illness.
Eg. Clostridium botolinum, Vibrio sp., Aeromonas sp.
b) Non-indigenous bacteria:-
They occur in seafood as
a result of contamination. The source include polluted aquatic environment,
sewage, excreta from animals, birds, human being, workers handling the material
as well as the surface and environment where the seafood is processed.
Example Salmonella sp, Shigella sp., E. coli, and Staphylococcus aureus
C)
Chemical spoilage (oxidation of the
fish lipids):-
Fish lipid is characterized by a high level of
polyunsaturated fatty acids (PUFA) and hence undergoes oxidative changes. With
fatty fish in particular, fat oxidation give rise to problem such as rancid
flavour and odor as well as discoloration. Lipid oxidation is by two process (a)
Auto oxidation – action of O2 on the unsaturated fatty acids and (b)
Lipid hydrolysis – an enzymatic hydrolysis with free fatty acids (FFA).
Oxidative rancidity is of great concern in the fatty fish storage. In pelagic
species like sardine, mackerel and herring, rancidity has been detected during
spoilage. At first hydro peroxide are formed, which further degrade to form
aldehyde and ketones with typical rancid flavor. The oxidation is initiated and
accelerated by heat, light (UV radiation), presence of several organic or
inorganic compounds (e.g. Cu and Fe), moisture content, large surface area,
presence of air etc. Antioxidant such as tocopherols, ascorbic acid, citric
acid or Carotenoids can inhibit oxidation.
Factors affecting
spoilage:-
The rate at which spoilage occur
varies with species of fish, sanitary conditions, methods of handling and
storage. The rate of spoilage is highly temperature dependent. Increase the
temperature from 0 to 50 C doubles the spoilage rate of many species
of fish. So, chilling the fish immediately after catch (rapid chilling),
careful handling, gutting and maintaining good hygiene will retard the spoilage
rate.
General Aspect of Sea Food Quality
Definition of Quality:-
Quality is generally considered as degree of excellence. It also related
to the price of the commodity, its composition nutritive value, degree of
freshness, hazards to health and satisfaction on eating.
Quality Assurance:-
At the
implementation level of quality assurance may be divided into two parts,
firstly “Quality Assurance” and secondly “Quality Control”.
Quality Assurance: -
This includes the following points.
1) Establish
good manufacturing practices suitable for unit.
2) Establish
product specifications.
3) Design
quality control programme.
4) Identify
critical control points for inspections.
5) Establish
laboratory procedure.
6) Ensure
regulatory compliance and safety in the plant.
7) Divide
programmes and procedures to improve yield.
8) Develop
effective market and product recall system.
Quality control:-
Quality
control in case of seafood is necessary steps, taken to protect the quality of
final product.
Uniqueness of seafood quality control
Quality
control of seafood differ that of any other food. Agricultural product can be
harvested under ideal condition that is right time food is harvested at right
time and right place. This meant that it is possible even to select the right
species to rare them at desire level of growth and harvest them in a predetermine
place as per predetermine scheduled. In the case of seafood harvesting is from
sea, rivers and other water areas from the stocks of unknown identity. Hence
the intrinsic quality varies in all possible variations. Another phenomenon
which complicates quality of seafood is unpredictability of catch. At time
catches may exceed the handling capacity. Sometimes catches are very poor and
processing unit may remain idol together. Another problem of tropical fishery
is presence of large number of spp.
Quality control setup
Depending
on size of production unit quality control is the responsibility of single
individual or department. The quality control unit should include
representative from all important section from seafood processing unit.
e.g.
Pre-processing , production, machine room, quality control room, packing.
Responsibilities of quality control
department
1. Formulation of
specification of raw materials, plant process, container and finish products.
2. Development of test procedure and testing of
quality of products.
3. Development of
sampling schedule.
4. Preparation of form
for recording and reporting.
5. Attending to any
problem during production and suggesting suitable solution.
6. Maintenance of
personal hygiene and sanitation.
7. Assuring the increase
customer satisfaction.
8. Training of personal
of labor.
9. On line inspection
with special reference to CCP.
10. Inspection and proper
storage packaging material.
11. Inspection and proper
storage of ingredients, cleaning agents and sanitizers.
12. Maintenance of
production and processing equipments also ensuring the proper maintenance of
cold storage.
13. Maintenance of the
laboratory and analysis of the same.
14. Checking the records
of the machine including log book of cold storage and freezers.
Quality problem in sea food industry-
Sea food
product can be broadly divided in to two groups,
1. Export
products
2. Domestic
product
The quality of product in both
cases has to be good. Some of the most common quality problems usually
encountered in these products are described below,
1. Poor
quality raw material- one can notice wild variations in quality of raw material
received in sea food plant.
2. This
problem is dependent on size of the fishing craft, facility for icing and
storage of fish onboard of fishing vessel. Facilities for further preservation
and storage at landing center. Sanitary condition onboard vessel, preprocessing
and processing vessel.
3. Following
pre-cautions need to be taken to maintain the quality of raw material.
a. Sand
adhering to fish or shrimp is washed off before starting any processing.
b. Dressing
should be carried out properly.
c. Broken
pieces should be kept separately in case of shrimp.
d. The raw
material temperature should be never being allowed to exceed 20C.
e. Good
quality ice and water should be used in processing.
f.
Strict hygienic and sanitation condition should
be maintained in processing.
Black spot in
shell on shrimp-
A black
spot formation in shrimp processing industry is enzymatic reaction and requires
access to oxygen addition to the presence of heavy metal like cupper and iron. The
pigments are produced by an oxidative reaction on tyrosine (amino acid). By
this discolourizition eating quality is not loosed but it mass appearance which
affect the marketing of shrimp. Melanosis can be prevented by cutting down
oxygen contact, lowering temperature or by using sodium metabisulphide or
potassium metabisulphide.
Inspection certification:-
Three systems of inspection
& certification have been recognized under the fish & fishery products.
They are,
1. Quality Control & Inspection in Approved
Units: -
QCIA unit should have the prescribed programme
supports and processing control. They also keep the necessary records. The
final product is subjected to regulatory agency such as EIA, to check whether
they meet to the all standards as prescribed or lay down. Standards are issued
with certificate for export. Regular
monitoring of the unit is also done to ensure the prescribed sanitary standards
are maintained or not and hygiene requirement are of complete satisfactory
levels.
1. In Process Quality Control: -
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