143
of filtration activity requires that the animals be not subjected to undue stress prior
to the depuration process. It means that the harvesting method and subsequent handling should not shock the animals too much and that they should not be exposed to
temperature extremes. Once placed in the system, the physiological conditions
should be such as to maximise the activity of the animals.
The sea water to be used in the depuration process must be disinfected during the
entry into the tanks and after being used in the tanks without being returned to the
system. Sea water used in depuration is disinfected with chlorine, UV light, ozone
and iodophors. Chlorine was one of the earliest means used to disinfect seawater for
depuration. When used with seawater of low to moderate sediment and organic
loads, it is an effective bactericide. However, there are concerns with its effectiveness against viruses (FAO 2008). In a study, three types of depuration methods were
tried for mussels (P. viridis) collected manually from natural beds. In the first one,
the mussels were washed thoroughly and filtered and then kept in filtered sea water
for 24 h. The second was kept in filtered and aerated water for 24 and 48 h. In the
third, the mussels were kept in filtered seawater and washed in filtered seawater
thoroughly after 2 h of chlorination at levels of 2.0, 2.5 and 3.0 ppm. According to
the results the bacterial load of the mussels was lowered effectively, either by washing in filtered sea water for 24 h or by keeping them in aerated sea water for 48 h.
Chlorination yielded the best results (Malarvanan and Edward 2002). Ren and Su
(2006) reported reduces in V. parahaemolyticus and V. vulnificus by application of
30 ppm chlorine. The advantage of ultraviolet light treatment is that it does not
change the chemical and physical properties of water while it purifies water. UV
light has been used for decontaminating seawater for shellfish purification. In one
study, it was reported that the levels of coliforms decreased in sea water, which was
subjected to UV treatment for 72 h (Vasconcelos and Lee 1972), and in another
study, it was reported that 2 h of UV treatment decreased the V. parahaemolyticus
population (Greenberg et al. 1982). Ozone has been shown to be effective in inactivating both bacteria and viruses by affecting their genetic material (RNA or DNA).
A decrease in Escherichia coli and V. parahaemolyticus populations was found in
mussels after being depurated in sea water containing 0.139 ppm ozone for 44 h
(Croci et al. 2002). A 2-log reduction in V. vulnificus has been reported after 24 h of
depuration in seawater containing 0.6–3.1 ppm ozone (Schneider et al. 1991). In
another study, a decrease in E. coli and coliforms was reported after ozone application (Maffei et al. 2009).
Shucking of Mussels
Shucking is the processing step that removes the edible portion of the mollusc from
the shell. It is usually done by hand, mechanically or through heat shock with steam
or hot water. This step may expose the product to microbiological or physical contamination. Physical removal of shellfish meat from the shell will often expose the
product to dirt, mud and detritus that should be removed before further processing
through washing (FAO 2008).
3.1 Bivalves
of filtration activity requires that the animals be not subjected to undue stress prior
to the depuration process. It means that the harvesting method and subsequent handling should not shock the animals too much and that they should not be exposed to
temperature extremes. Once placed in the system, the physiological conditions
should be such as to maximise the activity of the animals.
The sea water to be used in the depuration process must be disinfected during the
entry into the tanks and after being used in the tanks without being returned to the
system. Sea water used in depuration is disinfected with chlorine, UV light, ozone
and iodophors. Chlorine was one of the earliest means used to disinfect seawater for
depuration. When used with seawater of low to moderate sediment and organic
loads, it is an effective bactericide. However, there are concerns with its effectiveness against viruses (FAO 2008). In a study, three types of depuration methods were
tried for mussels (P. viridis) collected manually from natural beds. In the first one,
the mussels were washed thoroughly and filtered and then kept in filtered sea water
for 24 h. The second was kept in filtered and aerated water for 24 and 48 h. In the
third, the mussels were kept in filtered seawater and washed in filtered seawater
thoroughly after 2 h of chlorination at levels of 2.0, 2.5 and 3.0 ppm. According to
the results the bacterial load of the mussels was lowered effectively, either by washing in filtered sea water for 24 h or by keeping them in aerated sea water for 48 h.
Chlorination yielded the best results (Malarvanan and Edward 2002). Ren and Su
(2006) reported reduces in V. parahaemolyticus and V. vulnificus by application of
30 ppm chlorine. The advantage of ultraviolet light treatment is that it does not
change the chemical and physical properties of water while it purifies water. UV
light has been used for decontaminating seawater for shellfish purification. In one
study, it was reported that the levels of coliforms decreased in sea water, which was
subjected to UV treatment for 72 h (Vasconcelos and Lee 1972), and in another
study, it was reported that 2 h of UV treatment decreased the V. parahaemolyticus
population (Greenberg et al. 1982). Ozone has been shown to be effective in inactivating both bacteria and viruses by affecting their genetic material (RNA or DNA).
A decrease in Escherichia coli and V. parahaemolyticus populations was found in
mussels after being depurated in sea water containing 0.139 ppm ozone for 44 h
(Croci et al. 2002). A 2-log reduction in V. vulnificus has been reported after 24 h of
depuration in seawater containing 0.6–3.1 ppm ozone (Schneider et al. 1991). In
another study, a decrease in E. coli and coliforms was reported after ozone application (Maffei et al. 2009).
Shucking of Mussels
Shucking is the processing step that removes the edible portion of the mollusc from
the shell. It is usually done by hand, mechanically or through heat shock with steam
or hot water. This step may expose the product to microbiological or physical contamination. Physical removal of shellfish meat from the shell will often expose the
product to dirt, mud and detritus that should be removed before further processing
through washing (FAO 2008).
3.1 Bivalves