34
the animal to move in water. Due to biological growth, the animal should change its
shell several times in its life. This phenomenon is called moulting (Dang et al.
2018a). Shrimps should replace their shells to larger ones for growing. The physiology, morphology, and biochemistry of shrimp change during moulting process (Dall
et al. 1990). The connection of the shell to the muscle occurs via a collagen-like
connective tissue protein. The continuity of this attachment makes peeling difficult.
Shrimps can be peeled mechanically and manually. A typical shrimp peeling
machine has rubber coated adjacent piston cylinders. This machine operates according to the friction principle. A cylinder is strengthened and uses friction to rotate
other adjacent rollers. When the shrimp falls between the two rolls rotating in opposite directions, the rollers grasp the shells and pull them out of the meat (Lapeyre
et al. 2004). The machines are efficient in terms of time and labour, but sometimes
meat can break or not being fully peeled. Loss in tail segments due to strong adherence to the muscles during the peeling is an important problem of mechanical peeling (Linton and Gordon 1992). Mechanical shrimp peelers press down on shell
during peeling process and therefore it can break the meat. Due to these problems
of mechanical peelers, hand peeling is used as an alternative method. Compared to
mechanical peeling, hand peeling has advantageous such as keeping meat integrity
and reducing shell residues in the meat. However, hand peeling is costly, laborious,
time-consuming, and hazardous for food safety due to contamination.
Because of the negative effects of mechanical shell peelers on shrimp meat,
researchers have developed several methods to loosen shrimp shells before going to
the peeling machine. One of these methods is pre-cooking. In the peeling process
with the machine, it is reported that in pre-cooked shrimps more meat yield is
obtained and even the loss of the tail meat is reduced, and the shape and colour are
preserved. This is attributed to the expansion of the shell or the contraction and
compression of the meat or by a combination of both (Dang et al. 2018a).
However, thermal process is not suitable for every situation. Sometimes cookers
need raw shrimp meat. Another method applied is maturation when the cooking
process does not fully weaken the connection between the shell and the meat. Ice or
brine curing process was tried by the researchers before cooking. The maturation,
which is a traditional method, also has the characteristics of easy application and
cheapness. It has been reported that loosening in maturation method occurs via
enzymatic degradation of the connective tissue between the meat and the shell
(Taylor 1993).
Recent studies have focused on emerging methods to loosen shrimp shell. Thus,
it is aimed to perform mechanical peeling with less loss in shrimp meat. With the
idea that the connection between the shell and the meat can be broken by protein
denaturation, the studies are directed towards high hydrostatic pressure (HHP)
applications. Hansen and Nielsen (1988) developed a patented method. In this
method, the sudden pressure drop caused the water in the shell to warm up, causing
the loosening of the shell. Then, Yang et al. (2010) found that the pressure application of 200 MPa for 3 min was sufficient for peeling in shrimps (Penaeus vannamei). In another patented study, pressure application of between 224 and 327 MPa
2 Crustacean Shellfish
the animal to move in water. Due to biological growth, the animal should change its
shell several times in its life. This phenomenon is called moulting (Dang et al.
2018a). Shrimps should replace their shells to larger ones for growing. The physiology, morphology, and biochemistry of shrimp change during moulting process (Dall
et al. 1990). The connection of the shell to the muscle occurs via a collagen-like
connective tissue protein. The continuity of this attachment makes peeling difficult.
Shrimps can be peeled mechanically and manually. A typical shrimp peeling
machine has rubber coated adjacent piston cylinders. This machine operates according to the friction principle. A cylinder is strengthened and uses friction to rotate
other adjacent rollers. When the shrimp falls between the two rolls rotating in opposite directions, the rollers grasp the shells and pull them out of the meat (Lapeyre
et al. 2004). The machines are efficient in terms of time and labour, but sometimes
meat can break or not being fully peeled. Loss in tail segments due to strong adherence to the muscles during the peeling is an important problem of mechanical peeling (Linton and Gordon 1992). Mechanical shrimp peelers press down on shell
during peeling process and therefore it can break the meat. Due to these problems
of mechanical peelers, hand peeling is used as an alternative method. Compared to
mechanical peeling, hand peeling has advantageous such as keeping meat integrity
and reducing shell residues in the meat. However, hand peeling is costly, laborious,
time-consuming, and hazardous for food safety due to contamination.
Because of the negative effects of mechanical shell peelers on shrimp meat,
researchers have developed several methods to loosen shrimp shells before going to
the peeling machine. One of these methods is pre-cooking. In the peeling process
with the machine, it is reported that in pre-cooked shrimps more meat yield is
obtained and even the loss of the tail meat is reduced, and the shape and colour are
preserved. This is attributed to the expansion of the shell or the contraction and
compression of the meat or by a combination of both (Dang et al. 2018a).
However, thermal process is not suitable for every situation. Sometimes cookers
need raw shrimp meat. Another method applied is maturation when the cooking
process does not fully weaken the connection between the shell and the meat. Ice or
brine curing process was tried by the researchers before cooking. The maturation,
which is a traditional method, also has the characteristics of easy application and
cheapness. It has been reported that loosening in maturation method occurs via
enzymatic degradation of the connective tissue between the meat and the shell
(Taylor 1993).
Recent studies have focused on emerging methods to loosen shrimp shell. Thus,
it is aimed to perform mechanical peeling with less loss in shrimp meat. With the
idea that the connection between the shell and the meat can be broken by protein
denaturation, the studies are directed towards high hydrostatic pressure (HHP)
applications. Hansen and Nielsen (1988) developed a patented method. In this
method, the sudden pressure drop caused the water in the shell to warm up, causing
the loosening of the shell. Then, Yang et al. (2010) found that the pressure application of 200 MPa for 3 min was sufficient for peeling in shrimps (Penaeus vannamei). In another patented study, pressure application of between 224 and 327 MPa
2 Crustacean Shellfish