163
V. parahaemolyticus should be considered when classifying bivalve production
beds (Arik-Colakoglu et al. 2014). Other researchers have reported that 4-day depuration is sufficient for clams containing Salmonella in the category B limits, while
the C limits may be reduced by 50% over the same period (El-Shenawy 2004).
In a study to determine the depuration capacity of clams, Venus gallina were
contaminated with Vibrio parahaemolyticus and Vibrio vulnificus to determine
accumulation capacities in weak, medium, and highly contaminated waters. All
clams were exposed to contamination for 72 h. Depuration trials were performed in
close-circuit seawater-disinfection system that uses filtration, Ultraviolet and ozone.
Most of the depuration trials with V. parahaemolyticus showed a decrease in initial
bacterial loads after36–48 h, but in subsequent periods, the trend remained stationary. In V. vulnificus tests, clams showed a scarce depuration capacity instead (Barile
et al. 2018).
Depuration is not only effective on microbial contamination. The effects of depuration on heavy metals accumulation were also investigated. El-Shenawy (2004)
investigated clams (Ruditapes decussatus) harvested from two sites Timsah Lake,
Ismilia, Egypt and found that the bioaccumulation of metals varied strongly according to the sampling site. After 48 h of depuration, it was found that Fe, Ni, Co, Cu,
and Mn reduced significantly compared with the initial concentrations in clam tissue at the two stations.
Shucking of Clams
Most clams are shucked by hand. The hard clam is held in the palm of the hand with
the shell hinge against the palm. A strong, slender knife is inserted between the
valves and the shell is pried open, the abductor muscles cut, and the meat removed
from the shell. Other clams are also shucked by hand (Hackney 1990).
Surf clams, ocean quahogs, and occasionally large hard clams are shucked
mechanically. The clams are either placed on a flat conveyor belt and passed through
an open gas flame or are steamed at high temperature in pressure vessels. The heating, which often partially cooks the meat, greatly weakens the muscle shell bond,
and the meat is removed from the shell by tumbling. The meat and shells are separated in a brine tank. Surf clams, ocean quahog and large hard clams are often frozen after mechanical shucking. After the clams are removed from the shell, the
viscera are removed. The meats are then washed and cut or diced for packaging and
freezing (Hackney 1990).
Freshly harvested clams (Galatea paradoxa) from the Cross River, Nigeria, were
subjected to heat treatment (steam and water at 60, 70, 80, 90, 100 °C) for 1–6 min
after 24 h depurations. The effects of level of heat treatment on opening were evaluated. Some chemical shucking aids (NaOH, NaHCO 3 , Na 2 CO 3 , NaCl) in 60 °C
water was also used. According to the results boiling water was found most effective
in opening the clams. Shucking was achieved in 1 min as 100%. Steam was least
effective. For 100% opening needed 6 min in case of steam. In general, shucking
3.1 Bivalves
V. parahaemolyticus should be considered when classifying bivalve production
beds (Arik-Colakoglu et al. 2014). Other researchers have reported that 4-day depuration is sufficient for clams containing Salmonella in the category B limits, while
the C limits may be reduced by 50% over the same period (El-Shenawy 2004).
In a study to determine the depuration capacity of clams, Venus gallina were
contaminated with Vibrio parahaemolyticus and Vibrio vulnificus to determine
accumulation capacities in weak, medium, and highly contaminated waters. All
clams were exposed to contamination for 72 h. Depuration trials were performed in
close-circuit seawater-disinfection system that uses filtration, Ultraviolet and ozone.
Most of the depuration trials with V. parahaemolyticus showed a decrease in initial
bacterial loads after36–48 h, but in subsequent periods, the trend remained stationary. In V. vulnificus tests, clams showed a scarce depuration capacity instead (Barile
et al. 2018).
Depuration is not only effective on microbial contamination. The effects of depuration on heavy metals accumulation were also investigated. El-Shenawy (2004)
investigated clams (Ruditapes decussatus) harvested from two sites Timsah Lake,
Ismilia, Egypt and found that the bioaccumulation of metals varied strongly according to the sampling site. After 48 h of depuration, it was found that Fe, Ni, Co, Cu,
and Mn reduced significantly compared with the initial concentrations in clam tissue at the two stations.
Shucking of Clams
Most clams are shucked by hand. The hard clam is held in the palm of the hand with
the shell hinge against the palm. A strong, slender knife is inserted between the
valves and the shell is pried open, the abductor muscles cut, and the meat removed
from the shell. Other clams are also shucked by hand (Hackney 1990).
Surf clams, ocean quahogs, and occasionally large hard clams are shucked
mechanically. The clams are either placed on a flat conveyor belt and passed through
an open gas flame or are steamed at high temperature in pressure vessels. The heating, which often partially cooks the meat, greatly weakens the muscle shell bond,
and the meat is removed from the shell by tumbling. The meat and shells are separated in a brine tank. Surf clams, ocean quahog and large hard clams are often frozen after mechanical shucking. After the clams are removed from the shell, the
viscera are removed. The meats are then washed and cut or diced for packaging and
freezing (Hackney 1990).
Freshly harvested clams (Galatea paradoxa) from the Cross River, Nigeria, were
subjected to heat treatment (steam and water at 60, 70, 80, 90, 100 °C) for 1–6 min
after 24 h depurations. The effects of level of heat treatment on opening were evaluated. Some chemical shucking aids (NaOH, NaHCO 3 , Na 2 CO 3 , NaCl) in 60 °C
water was also used. According to the results boiling water was found most effective
in opening the clams. Shucking was achieved in 1 min as 100%. Steam was least
effective. For 100% opening needed 6 min in case of steam. In general, shucking
3.1 Bivalves