Fish degradation
From the moment of capture to its food use, fresh fish must necessarily be refrigerated. Storing the fish in ice at 0 ° C (constant temperature) does not alter its composition for about 4 - 7 days.
In addition to chemical transformations, fish can also be affected by contamination of biological origin. In particular, the fish is attacked mainly by bacteria belonging to the genera Pseudomonas, Moraxella And Flavobacterium-Cytophage.
Freshness assessment: how do you know if a fish is fresh?
Sensory methods
FRESH FISH
MISTER FISH
Smell
Soft and pleasant
Acre, acid, ammoniacal
General appearance
Brilliant, metallic, iridescent
Dull, dull
Body
Stiff
Soft (if you press the meat with a finger, the imprint remains)
Consistency
soda
Scales
Strongly adherent
They are easily removed
Skin
Tense, colorful
Flabby, faded
Eye
Clear, lively
Dull, glassy
Gills
Pink-red, united
Gray, lifted
Anus
Locked down
Protruding
Viscera
Smooth, clean, shiny
Soften
Plug
Adherent to the flesh
Relieved
Meat
Solid, white / red
Crumbly
Physical methods
Determination of the electrical conductivity of fabrics: as the fresh product deteriorates, the electrical conductivity increases.
Chemical methods
Determination of trimethylamine, volatile basic nitrogen, formaldehyde, histamine, peroxides and thiobarbituric acid.
Biochemical methods
Search for specific enzymes that escape from the cells during thawing; if they are present, it means that the fish has been frozen and refrozen.
Microbiological methods
They are based on the development of cultures of microorganisms, but they are too long to be applied to the evaluation of the freshness of fish.
When buying frozen fish, remember that the cold chain must be kept as intact as possible; for this reason:
put the frozen fish in the cart only when the shopping is finished (the seriousness of a supermarket is also evaluated on the basis of the position of the frozen food counter, which must be close to the cash desks and on the opposite side from the entrance).
In addition to evaluating the temperature of the thermostat in the refrigerated cabinet, preference must be given to the packages on the bottom, as those closest to the opening door are more subject to thermal changes.
Fish contaminants
They mainly derive from the environment in which they live. They can be divided into:
chemical contaminants:
- heavy metals: lead, cadmium, mercury
- pesticides
- organic chlorine and bromine compounds
and biological contaminants:
- toxins produced by algae and some fish species, such as puffer fish, can cause: poisoning with PSP paralysis; NSP neurotoxic poisoning; ASP amnesic poisoning; DSP diarrheal poisoning.
- parasites and microorganisms (they are more common in farmed fish).
storage
The best method for keeping fresh fish is refrigeration at 0 ° C, which can take place in cold rooms or on flake ice. In this case the commercial life of the fish is 7-8 days; 9-10 if it is vacuum packed.
Freezing (-18 -30 ° C), on the other hand, must take place in a maximum time of 2 hours and for this reason it is often done directly in the fishing boats. Other conservation processes, even if now used only to impart particular organoleptic characteristics, are:
- salting, in which the fish is alternated with layers of salt or immersed in concentrated brines (10-30% NaCl);
- l "smoking;
- drying (the "final humidity" must be less than 15% and its effectiveness is acceptable only for the conservation of lean fish, such as cod which is used to make stockfish);
- marinating (using vinegar and salt as preservatives);
The canning, very widespread in the industrial field, is used above all for tuna, mackerel and anchovies). By law, the addition of additives with antioxidant, antifungal, antibacterial action is allowed in canned fish:
- Sorbic acid and its salts
- Benzoic acid
- Paroxybenzoate of ethyl and propyl
- Sulfur dioxide (cod and shrimp and shellfish preserves)
- Ascorbic acid
The fish that remains unsold or the species caught with no commercial value are used for the production of fish meal and oil intended mainly for animal husbandry.
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