PRINCIPLES OF FISH PRESERVATION

Post Mortem CHANGES IN FISH
On the death of the fish, processes of physical and chemical change caused by enzymes and micro-organisms begin to occur. The complete decay of the fish is the final result of those changes.
Post-mortem changes which take place in fish tissue occur in the following phases:
– slime secretion on the surface of fish
– rigor mortis
– autolysis as enzymatic decomposition of tissues
– microbiological spoilage
The duration of each phase can change or phases can overlap. This depends on storage conditions, especially the temperature which greatly influences these processes.
Slime Secretion
Slime is formed in certain cells of fish skin and the process becomes very active just after fish death. Some of the fish, for example eel, secrete more slime than, for comparison, Salmonidae and perch. Fish which secrete great quantities of slime have poorly developed scales; very often the quantity of slime reaches 2-3% of the fish mass and that in turn creates problems during processing. The secretion process stops with the onset of rigor mortis.
Slime contains large amounts of nitrogenous compounds and these provide good nourishment for micro-organisms originating from the environment. Therefore, the slime spoils quickly: first giving an unpleasant smell to the fish, and second opening the way for further and deeper bacterial penetration into the fish.

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