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Bivalve molluscs, such as clams, oysters, scallops and mussels, have two main
shells or valves which are joined together by a hinge and held shut by adductor
muscles which function to open and close the valves which, when open, pump in sea
water containing food. One class of bivalve, which includes oysters and scallops,
contains one adductor muscle and is known as monomyrian. Another class, which
includes clams and mussels, contain two adductor muscles and is known as dimyrian (Hanks Jr and Grieb Jr 1971). The muscles are strong enough to close the valves
of the shell when they contract, and they are what enable the animal to close its
valves tightly when necessary, such as when the bivalve is exposed to the air by low
water levels, or when it is attacked by a predator. When the adductor muscles relax,
the valves of the shell are automatically pulled open to some extent by a ligament,
which joins the valves together and which is usually located on the hinge line
between the umbos of the shell. The resiliency of the ligament is what causes the
valves of the bivalve mollusc to open when the adductor muscles relax
(Wikipedia 2019f).
Heat shocking of molluscan shellfish is defined as a process that uses any form
of heat treatment such as hot water, water-saturated air, or dry heat for a short time
to facilitate detachment of meat from the shells. Heat treatment is not a cooking
process, but a method of removing only meat (FAO/WHO 2000). Opening the shells
with heat shock and removing the meat from the shell is done by steaming or dipping into boiling water. During this process, there is a loss of moisture in the meat,
protein degradation and a decrease in the juiciness of the meat which causes the
tissue to become rubber-like. At the same time, the original shape and structure of
mussels are lost during cooking. The mussels should first be washed and then either
steamed for about 4 min at 115.5 °C or for about 6 min in boiling water at 100 °C
or steam at atmosphere pressure; some processors prefer boiling to steaming since
the meats shrink less. Mussel meats immersed in boiling water are sterilized after
about 2½ min; additional processing time should be just sufficient to cook the meats
and no more, since overcooking causes excessive shrinkage of the meats. The liquor
produced can be kept if required for use in bottling or canning. The mussels should
be quickly cooled by water spray to prevent toughening of the meat (Waterman
1963). In the previous study, live green mussel (P. viridis) was subjected to heat
treatment by three different methods (hot water baths, water-saturated air, or dry
heat). Various time temperature combinations were used for this. The most effective
method for shucking was water bath followed by water-saturated air or dry heat. Hot
water bath treatment at 100 °C gave 100% open mussels (Azanza and Ventura 2005).
High pressure (HP) processing is a useful technology for shucking the raw meat
from the rigid shell of crustaceans and molluscs without cooking, thus meat removal
significantly more efficient without changing the size and shape of the meat retaining nutritional qualities. In a study, mussel meat treated at 100 MPa, was found
difficult to be shucked and remained attached to the shells by the adductor muscle
and at the edges of the mantle. In mussels treated at 200 MPa, the meat was easily
removed, but the adductor muscles remained on the shells. The meat got easily
detached from the shell, when subjected to 300 and 400 MPa pressure treatment.
Application of HP increased the hardness of mussel tissue. The author stated that
this increase in the texture may be due to the protein-protein interactions which
3 Molluscan Shellfish
Bivalve molluscs, such as clams, oysters, scallops and mussels, have two main
shells or valves which are joined together by a hinge and held shut by adductor
muscles which function to open and close the valves which, when open, pump in sea
water containing food. One class of bivalve, which includes oysters and scallops,
contains one adductor muscle and is known as monomyrian. Another class, which
includes clams and mussels, contain two adductor muscles and is known as dimyrian (Hanks Jr and Grieb Jr 1971). The muscles are strong enough to close the valves
of the shell when they contract, and they are what enable the animal to close its
valves tightly when necessary, such as when the bivalve is exposed to the air by low
water levels, or when it is attacked by a predator. When the adductor muscles relax,
the valves of the shell are automatically pulled open to some extent by a ligament,
which joins the valves together and which is usually located on the hinge line
between the umbos of the shell. The resiliency of the ligament is what causes the
valves of the bivalve mollusc to open when the adductor muscles relax
(Wikipedia 2019f).
Heat shocking of molluscan shellfish is defined as a process that uses any form
of heat treatment such as hot water, water-saturated air, or dry heat for a short time
to facilitate detachment of meat from the shells. Heat treatment is not a cooking
process, but a method of removing only meat (FAO/WHO 2000). Opening the shells
with heat shock and removing the meat from the shell is done by steaming or dipping into boiling water. During this process, there is a loss of moisture in the meat,
protein degradation and a decrease in the juiciness of the meat which causes the
tissue to become rubber-like. At the same time, the original shape and structure of
mussels are lost during cooking. The mussels should first be washed and then either
steamed for about 4 min at 115.5 °C or for about 6 min in boiling water at 100 °C
or steam at atmosphere pressure; some processors prefer boiling to steaming since
the meats shrink less. Mussel meats immersed in boiling water are sterilized after
about 2½ min; additional processing time should be just sufficient to cook the meats
and no more, since overcooking causes excessive shrinkage of the meats. The liquor
produced can be kept if required for use in bottling or canning. The mussels should
be quickly cooled by water spray to prevent toughening of the meat (Waterman
1963). In the previous study, live green mussel (P. viridis) was subjected to heat
treatment by three different methods (hot water baths, water-saturated air, or dry
heat). Various time temperature combinations were used for this. The most effective
method for shucking was water bath followed by water-saturated air or dry heat. Hot
water bath treatment at 100 °C gave 100% open mussels (Azanza and Ventura 2005).
High pressure (HP) processing is a useful technology for shucking the raw meat
from the rigid shell of crustaceans and molluscs without cooking, thus meat removal
significantly more efficient without changing the size and shape of the meat retaining nutritional qualities. In a study, mussel meat treated at 100 MPa, was found
difficult to be shucked and remained attached to the shells by the adductor muscle
and at the edges of the mantle. In mussels treated at 200 MPa, the meat was easily
removed, but the adductor muscles remained on the shells. The meat got easily
detached from the shell, when subjected to 300 and 400 MPa pressure treatment.
Application of HP increased the hardness of mussel tissue. The author stated that
this increase in the texture may be due to the protein-protein interactions which
3 Molluscan Shellfish