Spoilage of fish is a process of deterioration in the quality of fish, which changes its appearance, odour and taste. The breakdown of biomolecules like proteins, amino acids and fats in the fish are the factors responsible for fish spoilage. Thus, a fish can be spoiled by either chemical or biological degradation.

1. Fish Spoilage

2. A series of complicated metabolic process
Enzymes and bacteria
Undesirable or unacceptable
Changes in sensory characteristics.
SPOILAGE CONCEPT
Fish is one of the most perishable food items
FRESH FISH???? SPOILED FISH????
Food spoilage is considered as any change that renders the product
unacceptable for human consumption

3. Fish Die
Rigor Mortis
Autolysis
Microbial Activity
Spoilage
Sequence of events during spoilage

4. RIGOR MORTIS
 Progressive stiffening of muscle shortly after death
 Starts from the tail towards the head
 Duration depends on
 Species of fish
 Size
 Catching method
 Handling of fish
 Temperature
 Physical condition of the fish

5. Why does a fish spoil?
Blood circulation stops Oxygen supply fails
Energy production stops Respiration ceases
Acid forms in muscles
Muscle stiffing
Muscle softing
Tissue breakdown
Bacterial growth
Aerial oxidation
FISH
Fig: Factors and causes of fish spoilage

6. Fish spoils for three reasons/modes of spoilage
 Action of enzymes/Autolytic enzymatic spoilage
 Action of bacteria/Bacterial spoilage
 Oxidation of lipid/Oxidative spoilage
Bacterial spoilage is the most important cause of
fish spoilage

7. Autolytic spoilage (Enzymatic)
Major changes/events during enzymatic/autolytic spoilage
 Rigor mortis
Glycolysis
 Autolytic enzyme action and flavor changes (Necleotide
degradation)
Belly bursting
 Color changes

8. The autolytic changes that occur in chilled/frozen fish (FAO, 2005)
Autolytic spoilage (Enzymatic)

9.  The subsurface flesh of live healthy fish is usually sterile and does not contain any bacteria
or other organisms.
 But, microorganisms colonize the skin, gills and the gastrointestinal tract of fish. The
geographical location, the season and the method of harvest are the reasons deciding the
number and diversity of microbes.
 The natural fish microflora tends to reflect the microbial communities of the surrounding
waters.
 Fish harvested from eutrophic and warm waters will present higher bacterial numbers than
fish from clean and cold waters.
 Gram-negative genera including: Acinetobacter, Flavobacterium, Moraxella, Shwenella and
Pseudomonas dominates the autochthonous bacteria flora of fish.
 Vibrio, Photobacterium and Aeromonas spp. are also common aquatic bacteria, and typical
of fish flora.
 Gram-positive organisms such as Bacillus, Micrococcus, Clostridium, Lactobacillus and
coryneforms can also be found in varying proportions on fish.
Pseudomonas, Flavobacteria, Acinetobacter, Aeromonas and Moroxella are
important Spoilage organisms.
Microbial spoilage

10. Major deteriorative changes brought about by microorganisms/bacteria
 Formation of ammonia
Formation of TMA
Histamine formation
 Indole production
 Other volatile sulphur compounds
Microbial spoilage

11. Substrate Product by bacterial
activity
Odor
Inosine Hypoxanthine Characteristics odor
Methionine and
Cystine
H2S
Methyl mercapton,
Characteristics odor,
Cabbage like or strong
sulphide,
Carbohydrate and
lactate
Acetic acid,
CO2+H2O
Glycine,
Sesine,
Leusine
Acetic ,
Butyric &
Propionic acid
Fruity
TMAO TMA Fishy or Ammonical
Urea/amino acid NH3 Fishy or ammonical
Substrate and off-odour/off-flavour compounds produced by bacteria
during spoilage of fish
Microbial spoilage

12. lists spoilage bacteria in descending order of spoilage activity.
The compounds formed during spoilage through microbial metabolism
Microbial spoilage

13. Involved in fish spoilage at normal temperature:
1. Escherichia coli
2. Proteus
3. Serratia
4. Sarcina
5. Clostridium
Spoilage of special kinds of fish and sea foods:
Salt fish spoiled by : Serratia, Micrococcus, Bacillus,
Pseudomonas.
Smoked fish : Molds
Marinated (Sour pickled) fish : Lactic acid bacteria.
Canned fish : Clostridium botulinum, .
Chilled Shrimp : Achromobacter , Pseudomonas.
Raw lobsters : Pseudomonas, Bacillus.
Oyesters : Asparegenous yeast.

14. Oxidative spoilage
 Lipid oxidation is a major cause of deterioration and spoilage for the pelagic fish
species such as mackerel and herring with high oil/fat content stored fat in their flesh
 Lipid oxidation involves a three stage free radical mechanism: initiation, propagation
and termination
 In fish, lipid oxidation can occur enzymatically or non-enzymatically.
 The enzymatic hydrolysis of fats by lipases is termed lipolysis (fat deterioration).
During this process, lipases split the glycerides forming free fatty acids which are
responsible for: (a) common offflavour, frequently referred to as rancidity and (b)
reducing the oil quality
The enzymes involved are the lipases present in the skin, blood and tissue. The main
enzymes in fish lipid hydrolysis are triacyl lipase, phospholipase A2 and phospholipase

15. .
Phases of spoilage

16. CHANGES IN EATING QUALITY OF FISH IN ICE
Phase 1
 The fish is very fresh and has a sweet, seaweedy and delicate taste.
 The taste can be very slightly metallic.
Phase 2
 There is a loss of the characteristic odour and taste.
 The flesh becomes neutral but has no off-flavours.
 The texture is still pleasant
Phase 3
 There is sign of spoilage and a range of volatile, unpleasant-smelling
substances is produced depending on the fish species and type of spoilage
(aerobic, anaerobic).
 One of the volatile compounds may be trimethylamine (TMA) derived from
the bacterial reduction of trimethyl-aminoxide (TMAO).
 TMA has a very characteristic "fishy" smell.
 At the beginning of the phase the off-flavour may be slightly sour, fruity
and slightly bitter, especially in fatty fish.
 During the later stages sickly sweet, cabbage-like, ammoniacal,
sulphurous and rancid smells develop.
 The texture becomes either soft and watery or tough and dry.
Phase 4
 The fish can be characterized as spoiled and putrid

17. Evidence of Fish spoilage
Factors influencing kind and rate of spoilage
How does fish spoilage accelerate?
How can we delay or stop fish spoilage

18. Evidence of Fish spoilage:
 Eyes dull and sunken
 Gills no longer red, but pale pink, brownish or grey and
putrid smell.
 Anus wet, swollen and red
 Surface of fish dull, covered with opaque slime, sour or
putrid smell.
 Flesh very soft and flabby. Abnormally grey or reddish in
color, moldy, sour or putrid smell.

19. Factors influencing kind and rate of spoilage:
1. The kind of fish:
2. The condition of the fish when caught
3. Kind and extent of contamination
4. Temperature

20. Factors influencing kind and rate of spoilage:
1. The kind of fish:
 Flat fish spoil more rapidly than round fish because they pass through rigor
mortis more rapidly.
 Certain fatty fish deteriorate rapidly because of oxidation of the
unsaturated fats of their oils.
 Fishes in high TMAO soon produce appreciable amount of the fish flavor of
TMA.
2. The condition of the fish when caught:
 Fish that are exhausted as a result of struggling , lack of O2 and excessive
handling spoil more rapidly because of the exhaustion of glycogen, hence
smaller drop pH .
 Feedy fish those full of food when caught, are more perishable than those
with an empty intestinal tract.

21. 3. Kind and extent of contamination
 Come from mudwater, handlers, and the exterior slime and intestinal content
of the fish and
The greater the load of bacteria on the fish, the more rapid the spoilage.
4. Temperature:
Chilling the fish is the most commonly used method for preventing spoilage.
Cooling should be as rapid as possible to 00-10 C. The warmer the
temperature, the shorter the storage life of the fish.
Prompt and rapid freezing of the fish is more effective in preservation.
Factors influencing kind and rate of spoilage:

22. How does fish spoilage accelerate?
Spoilage of fish is accelerated by-
 Struggle/excitation during fishing
 Rough handling, injury or damage of muscle
 Improper sanitation
 Contamination
 Delay of icing
 Exposed to sun at any stage
Delay of icing is the most important critical factor
that accelerates the spoilage

23. How can we delay or stop fish spoilage
Fish spoilage can be delayed or stopped by
 Protecting fish from physical injury or muscle destruction
 Applying proper sanitation and avoiding contamination
 Lowering temperature immediately: keeping cool during transportation and
storage
 Destroying enzyme and killing bacteria by high temperature: canning, heat
processing
 Reducing water content in fish body: drying, salting, smoking