Post Harvest Spoilage of Fish

1. Post Harvest Spoilage
of Fish
Dr.Laximan Sawant

2. • Fish is a perishable commodity
• Spoilage of fish begins as soon as the fish dies
• In tropical countries fish spoil quite rapidly within
a few hours of landing , if not properly cooled .

3. In raw fish spoilage takes place
mainly due to
• Biological action
– Enzymatic action
– Microbial action
• Chemical action

4. Raw fish
spoilage
Biological Chemical
action action
Enzymatic Microbial
action action
Yellowing of fish
flesh

5. • Enzymes and bacteria do not cause any deteriorative
changes in the living cell because of natural defense
mechanism.
• In dead fish enzyme become involved in autolytic
changes and bacteria invade the fish muscle and
proliferate there
• Responsible for early loss of quality of fresh fish

6. Glycolysis
Flavour changes in
fish
Black
discolouration
Belly bursting
Yellowing of fish
flesh
Colour
Changes
Brown
discolouration

7. Microbial spoilage
Saprophytic
Histamine Formation of Formation of
Indole production Other compounds
formation ammonia TMA
Pathogenic
bacteria
Indigenous Non-Indigenous
bacteria bacteria

8. 1. Glycolysis
• The first enzymatic change in fish muscle is the
gradual hydrolysis of glycogen to lactic acid which
is known as glycolysis
• After death, the blood circulation stops and the cells
are no longer supplied with oxygen and hence
glycogen will not be converted into carbon dioxide
& water
• In P.M. period , glycolysis proceeds via anaerobic
pathway where end product is lactic acid, as lactic
acid accumulates pH of muscles fall .

9. • In general, fish muscles contains relatively low
amount of glycogen compared with mammalian
muscle, & the final pH is consequently higher.
This makes fish meat more susceptible to microbial
attack
• Rested fish contains more glycogen than exhausted
fish , & well fed fish more than starved fish

10. 2.Flavour changes in fish ( Nucleotide
degradation)
• The most significant enzyme deterioration are those
which affects flavour.
• Nucleotide degradation in fish muscle produces many
flavour bearing compounds
• These compounds are formed by splitting of ATP by
series of dephosphorylation and deamination
reactions

11. ATP ADP AMP IMP Inosine Ribose
Hypoxanthine
• At ambient temp. ATP breaks down rapidly and IMP
(Inosine monophosphate) accumulates in the fish
tissue
• In fresh fish IMP is very high and imparts a desirable
sweet, meaty & characteristic flavour to fish.

12. • As autolysis proceeds further , the level of IMP decreases ,
& neutral tasting inosine or bitter tasting hypoxanthine
accumulates in the tissue as a result fish becomes more
Insipid.

13. 3.Belly bursting
• Enzymatic spoilage causes belly bursting of fish,
especially during a period of high food intake.
• These fish will have large content of digestive
enzymes in digestive tract. Such fish will degrade
quickly & spoil easily soon after caught.

14. • In the dissolved gut components, bacteria proliferate
and produces gases such as Co2 & H2
• This gas production leads to belly bursting after short
storage period

15. 4.Colour Changes in fish
I. Black discolouration –
• It is due to oxidative reaction of tyrosinase on
tyrosine.
o Sulphite preservatives are used to prevent black
discolouration.
o Shrimps are dipped in 0.2-0.5 % sodium bisulphite
for one minute

16. II. Yellowing of fish flesh
• Frozen storage of some fish may result in
yellowing of flesh below skin.
• Freezing process disrupt chromatophores and
release carotenoids and their migration to the S/C
fat layers causes yellowing.

17. III. Brown discolouration
• Cause by reaction of protein or amino acid with
product of lipid oxidation
• It is observed in variety of processed products
including white pomfret, sardine etc
• Discolouration due to protein-lipid browning is
greater in fatty fish than lean fish

18. Microbial spoilage
• Fish spoilage is mainly due to action of bacteria.
Bacteria are present on the surface slime, skin, gills &
intestine of fish.
• In dead fish bacteria begin invading the tissues
causing spoilage and production of undesirable
compounds.

19. • In food processing industry two types of
micro-organism are of concern
– Saprophytic
– Pathogenic bacteria

20. Saprophytic / Spoilage Bacteria
• These are responsible for spoilage of fish
• Important class of spoilage organism are –
Pseudomonas , Acinobacter, Aeromonas &
Moraxella
• Flesh looses its qualities like juiciness, firm texture,
etc changing it into a product that becomes soft with
loss of flavour, discolouration & off flavour

21. Major deteriorative changes brought
about by microorganism in fish are
a. Histamine formation
b. Indole production
c. Formation of ammonia
d. Formation of TMA
e. Other compounds

22. Histamine formation
• Microbial spoilage of fish produces histamine in
certain species
• Dark muscle fishes contain high levels of free amino
acids, histidine in their muscle
• During spoilage histidine is converted into histamine
• Histamine increases with temperature & 37 C is the
optimum temperature
• Morganella morganii, Klebsiella pneumoniae are the
spoilage organism producting histamine

23. 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

24. Formation of ammonia
• Spoilage organism convert many nitrogen compounds
into off smelling volatile bases
• The free amino acid pool in the muscle of fish is readily
utilized by spoilage organism by the process of
deamination resulting in formation of ammonia which is
primary compound formed during decomposition.

25. • Urea present in sharks & rays is degraded to
ammonia by bacterial action. Thus high level of
ammonia in these species is an indication of spoilage

26. Formation of TMA
• Marine fish is characterized by the presence of an
odourless compound called trimethylamine oxide
(TMAO).
• Spoilage organism convert this TMAO into foul
smelling trimethylamine (TMA)

27. Other compounds
• Includes various volatile compounds like H2s,
deimethysulphide & methylmercaptan.
• Esters of lower fatty acids such as acetic, propionic,
butyric acids are also produced
• Volatile sulphur compounds influence the organoleptic
characters.

28. Pathogenic bacteria
• Pathogenic bacteria associated with sea
food are of two types
– Indigenous bacteria
– Non-Indigenous bacteria

29. Indigenous bacteria
• These are widely distributed in the aquatic environment.
• These pathogens occur in minimal numbers & are not a
serious problem in fresh fish
• However their growth & multiplication in sea food is
serious problem & can cause illness
• Eg.- Clostridium botulinum , Vibrio sp., etc

30. Non-Indigenous bacteria
• They occur in seafood as a result of contamination.
• Source include polluted aquatic environment, sewage,
workers handling as well as the surface where the sea
food is processed.
• Eg- Salmonella sp , E. coli , Shigella

31. Chemical spoilage
• The most common chemical action which causes
spoilage is the oxidative rancidity in fatty fishes.
• Fish is characterized by a high level of polyunsaturated
fatty acids (PUFA) & hence under goes oxidative
changes.

32. • With fatty fish in particular, fat oxidation give rise to
problems such as rancid flavour and odour as well as
discolouration
• At first hydro-peroxides are formed , which further
degrade to form aldehyde and ketones with typical
rancid flavour.