Biology Reference
In-Depth Information
Marinated Fish
Safe processing is primarily based on the level of NaCl in the tissue fl uid.
When the minimum amount of acetic acid (2.5-3.0% in the tissue fl uid)
is used, the following maximum, survival time of nematodes at various
NaCl-levels was found: Maximum survival times of nematodes should
therefore also be minimum holding time of the fi nal product before sale.
Table 4.8
Survival of nematodes at different NaCl-levels
% NaCl in tissue fl uid
Max. survival time of nematodes
4-5
6-17 wk
6-7
10-12 wk
8-9
5-6 wk
Heat-treated Fish
All nematodes are killed when heated to 55°C for 1 min. This means
that hot-smoked, pasteurized, sous-vide cooked and other lightly heat-
treated fi sh products are safe. However, some normal household cooking
traditions may be on the borderline of safety.
Frozen Fish
Freezing to - 20°C and maintaining this temperature for at least 24 h will
kill all nematodes. The results listed above show that a number of fi sh
products are unsafe. This applies to lightly salted fi sh products (< 5-6%
NaCl in water phase) such as matjes-herring, gravad fi sh, cold smoked
fi sh, lightly salted caviar, ceviche and several other local traditional
products. A short period of freezing either of the raw material or the fi nal
product therefore must be included in the processing as a means of control
of parasites.
BIOTOXINS
It has been known since ancient times that certain fi sh and shellfi sh
are poisonous and can cause death when eaten. The fi rst Chinese
pharmacopoeia, dating 2800 BC, records injunctions against eating puffer
fi sh (Kao, l966).
The chemical nature and biological basis for these food-borne
intoxications have been elucidated over the last 50 yr, beginning with
the pioneering work of Meyer and Sommer on the etiology of paralytic
shellfi sh poisoning (PSP) in California (Meyer et al., l928). It is now
evident that certain microscopic algae, present in phytoplankton, produce
very potent toxins (phycotoxins, or algal toxins), which are chemical
compounds mainly of low relative molecular mass. Concentrations of
phycotoxins in the sea or in freshwater are highest during an algal bloom
