8/12/2019 FAO Fisheries & Aquaculture - Post-harvest Changes in Fish

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Fish spoiling in a port

FAO/FIIU Photo Library

Food and Agriculture Organization of the United Nations

for a world without hungerFisheries and

Aquaculture Department

Post-harvest changes in fish

Immediately after capture, several chemical and biological

changes take place in dead fish which can ultimately lead

to rejection for human consumption because of spoilage.

Fish post-harvest losses are significant, especially in

developing countries. Estimated at 10 to 12 million tonnes,

they account for around 10 percent of global capture and

cultured fish. Therefore, understanding the post-harvest

changes that occur in fish is very important in developing

appropriate measures to reduce losses and preserve the

quality and safety of the finished products.

The most obvious changes fish undergo after capture are

sensory, the foremost being the onset of rigor mortis due

to a loss of the limp elastic texture of the muscle which

contracts before becoming hard and stiff. This condition usually lasts for a day or

more in iced fish, then rigor resolves. Other changes relate to the appearance,

odour, texture and taste.

Sensory changes of fish are due to the enzymatic breakdown of major fish

molecules. These reactions are catalysed either by autolytic or bacterial enzymes,

as summarized in the table below.

Summary of Autolytic Changes in Chilled or Frozen Fish

Enzyme(s) Substrate Changes Encountered Prevention

glycolytic enzymes Glycogenproduction of lactic acid, pH of

tissue drops, loss of water-holding

capacity in musclehigh temperature rigor may result

in gaping

fish should be allowed to pass through

rigor at temperatures as close to 0C as

practically possiblepre-rigor stress must be avoided

autolytic enzymes

involved in

nucleotide

breakdown

ATP

ADP

AMP

IMP

loss of fresh fish flavour, gradual

production of bitterness with Hx*

(later stages)

same as above

rough handling or crushing accelerates

breakdown

cathepsins proteins,

peptides softening of tissue making

processing difficult or impossible

avoid rough handling during storage

and discharge

chymotrypsin,

trypsin, carboxy-

e tidases

proteins,

peptides autolysis of visceral cavity in

pelagics (belly-bursting)

problem increased with

freezing/thawing or long- term chill

Related topics

HACCP

Reducing post-harvest

losses

Related documents

Quality and changes in

fresh fish

A Study of the Options

for Utilization of

Bycatch and Discards

from marine capture

Fisheries

Related links

Fisheries and food

security: Post-harvestlosses in artisanal

fisheries

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8/12/2019 FAO Fisheries & Aquaculture - Post-harvest Changes in Fish

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storage

calpain Myofibrillar

proteins softening

molt-induced softening, in

crustaceans

removal of calcium thus preventing

activation

collagenases Connective

tissue gaping of filletssoftening of muscle tissue

connective tissue degradation related totime and temperature of chilled storage

TMAO demethylase TMAOformaldehyde

induced toughening of frozen

gadoid fish

store fish at temperatures less than or

equal to -30C

physical abuse and freezing/thawing

accelerate formaldehyde-induced

toughening

*: Hx: Hypoxanthine. TMAO: Trimethylamine oxide

Microbially induced changes result from bacteria found on all the outer surfaces (skin and gills) and in the

intestines of live and newly-caught fish. These bacteria invade the muscle and cause gradual degradation of

several of its constituents (carbohydrates, nucleotides, amino acids and other NPN molecules), producing

undesirable volatile compounds such as trimethylamine, volatile sulphur compounds, aldehydes, ketones, esters

and hypoxanthine, as well as other low molecular weight compounds.

The last cause of fish spoilage is lipid oxidation and hydrolysis that leads to the development of rancidity, even

with storage at subzero temperatures. This is due to the large amount of polyunsaturated fatty acid moietiesfound in fish lipids. In fact, this is a major cause of spoilage of frozen fish.