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Keeping and Processing Clams Alive
Bivalve, including clams, often are presented to the consumer in the live state; however, they are often processed for the live market. Bivalves can survive out of the
water for extended periods, which allows them to go through the processing chain.
Clams can be stored wet or dry to keep alive. Freshly harvested clams (Galatea
paradoxa) obtained from the Cross River, Nigeria were subjected to live storage for
7 days in or outside of water. It was determined that 57% of wet clams and 35% of
dry clams died in 7 days. There was no death on day 1 in wet storage, but no death
on day 1–3 in dry storage. Dry storage was found to be effective in reducing postharvest mortality and weight loss and would increase profitability in the clam industry (Ekanem and Achinewhu 2006).
Depuration of Clams
Depuration is a process in which shellfish are placed in tanks with clean seawater
and allowed to continue their natural filter feeding activities by cleaning themselves
from sewage contaminants. Many factors such as, water quality, oxygenation and
flow rates of water, temperature, water to bivalve ratio, salinity, removal, and deposition, of faecal material, purification and system design affect the depuration
process.
In a study based on microbiological indices before and after depuration, the survival rate of depurated clams (C. gallina) and meat yields were investigated. After
landing, clams harvested from offshore natural beds transported to the depuration
plant. Depuration was performed monthly for 1 year. At the end of the study,
Escherichia coli decreased by 62% and fecal coliforms decreased by 54%. The
authors reported that after 24 h of depuration, except for August, the faecal coliform
count of all samples was below the legal limits and that E. coli was above the limits
in December and January. While no decrease in E. coli in August was reported, there
was a decrease in other samples. Between March and September, Salmonella spp.
and Vibrio parahaemolyticus were not detected, while Vibrio alginolyticus was
detected. All these results showed that the effects of depuration conditions on microbiological quality were variable. On the other hand, meat yield and survival rate of
C. gallina were not affected by depuration process (Maffei et al. 2009).
In another study aimed to determine the depuration times of Donax trunculus
and Tapes decussatus, clams were contaminated with Escherichia coli, Salmonella
enterica subsp. enterica serovar Typhimurium and Vibrio parahaemolyticus. Clams
harvested from natural beds in Çanakkale Strait and Marmara Sea (Turkey) were
depurated in tanks having filtration and ozone system. As a result of the study, it was
determined that the bacteria load of both clams decreased by 40% in the first 12 h.
Depuration time for all bacteria was determined as 66 s for T. decussatus. For
D. trunculus, the situation was slightly different. Depuration time for S. typhimurium
was found to be 66 h and for E. coli was 78 h. However, V. parahaemolyticus was
detected at 1.7 Log10 cfu/g even after 72 h. Therefore, it has been proposed that
3 Molluscan Shellfish
Keeping and Processing Clams Alive
Bivalve, including clams, often are presented to the consumer in the live state; however, they are often processed for the live market. Bivalves can survive out of the
water for extended periods, which allows them to go through the processing chain.
Clams can be stored wet or dry to keep alive. Freshly harvested clams (Galatea
paradoxa) obtained from the Cross River, Nigeria were subjected to live storage for
7 days in or outside of water. It was determined that 57% of wet clams and 35% of
dry clams died in 7 days. There was no death on day 1 in wet storage, but no death
on day 1–3 in dry storage. Dry storage was found to be effective in reducing postharvest mortality and weight loss and would increase profitability in the clam industry (Ekanem and Achinewhu 2006).
Depuration of Clams
Depuration is a process in which shellfish are placed in tanks with clean seawater
and allowed to continue their natural filter feeding activities by cleaning themselves
from sewage contaminants. Many factors such as, water quality, oxygenation and
flow rates of water, temperature, water to bivalve ratio, salinity, removal, and deposition, of faecal material, purification and system design affect the depuration
process.
In a study based on microbiological indices before and after depuration, the survival rate of depurated clams (C. gallina) and meat yields were investigated. After
landing, clams harvested from offshore natural beds transported to the depuration
plant. Depuration was performed monthly for 1 year. At the end of the study,
Escherichia coli decreased by 62% and fecal coliforms decreased by 54%. The
authors reported that after 24 h of depuration, except for August, the faecal coliform
count of all samples was below the legal limits and that E. coli was above the limits
in December and January. While no decrease in E. coli in August was reported, there
was a decrease in other samples. Between March and September, Salmonella spp.
and Vibrio parahaemolyticus were not detected, while Vibrio alginolyticus was
detected. All these results showed that the effects of depuration conditions on microbiological quality were variable. On the other hand, meat yield and survival rate of
C. gallina were not affected by depuration process (Maffei et al. 2009).
In another study aimed to determine the depuration times of Donax trunculus
and Tapes decussatus, clams were contaminated with Escherichia coli, Salmonella
enterica subsp. enterica serovar Typhimurium and Vibrio parahaemolyticus. Clams
harvested from natural beds in Çanakkale Strait and Marmara Sea (Turkey) were
depurated in tanks having filtration and ozone system. As a result of the study, it was
determined that the bacteria load of both clams decreased by 40% in the first 12 h.
Depuration time for all bacteria was determined as 66 s for T. decussatus. For
D. trunculus, the situation was slightly different. Depuration time for S. typhimurium
was found to be 66 h and for E. coli was 78 h. However, V. parahaemolyticus was
detected at 1.7 Log10 cfu/g even after 72 h. Therefore, it has been proposed that
3 Molluscan Shellfish