98
undergo autoxidation and polymerization to form dark pigments. PPO is responsible for the sclerotization (hardening) of the exoskeleton after moulting. Cuticle
hardening occurs when the quinones produced from diphenol oxidation form crosslinks between adjacent protein chains (Stevenson 1985). Factors affecting blackspot
in shrimps and lobsters include method of capture, catch handling, age, and sex.
polyphenoloxidase (PPO) activity was measured in cuticles of Norwegian lobsters
caught over a 7-month period. It was observed that PPO activity increased in early
August and early October, but the high PPO activity detected in May showed the
spring moulting period. Exposure to damage and stress of Norwegian lobsters was
associated with an increase in PPO activity. No correlation was observed between
initial PPO activity and black spot development during the storage of Norwegian
lobsters. This showed that biochemical events during storage were more than the
initial PPO level for black spot development. The times during the year during
which the Norway lobsters are more likely to moult are dependent on sex and maturity, but also differ from region to region. On reaching sexual maturity, male Norway
lobsters moult twice a year until they are 6–7 years old, whereas females moult
once, or not at all, in a given year. Longer trawl hauls and rough handling on board
would lead to the loss of claws, whereas, conversely, short hauls and gentle handling
of the catch on board would preserve more Norway lobsters intact. Thus, missing
claws reflect rough treatment of the Norway lobsters both during and after the haul.
A linear correlation was found between the number of remaining claws on the
Norway lobsters and PPO activity. This suggests that rough handling of the Norway
lobster catch is associated with an increase in PPO activity in the lobsters (Bartolo
and Birk 2002).
Melanosis has been reported to occur due to the presence of high levels of polyphenoloxidase (PPO) in cephalotorax of lobsters (Martínez-Alvarez et al. 2008b).
Rough handling of lobsters and other traumatic events trigger the defence mechanism of these organisms having PPO activity, resulting in increased blackening.
Even when they are alive, they can be encouraged to develop melanosis because of
any injury (Ogawa et al. 1984). The blackening of the broken clamped legs, parapods and carapax is caused by hemocyanin from PPO (Gimenez et al. 2010).
Inhibition of melanosis catalyzed by polyphenoloxidases is inhibited by bisulphites
by reaction with quinones forming sulphoquinones (Ferrer et al. 1989).
In various studies, different inhibitors were used for inhibition of melanosis in
lobsters and positive results were obtained. Brack et al. (2008) found that Mimosine
inhibits monophenol and diphenoloxidase activity of European spiny lobster
(Palinurus elephas). Opoku-Gyamfua et al. (1992) reported inhibition effect of
EDTA (ethylenediamine tetra acetic acid) on PPO from lobster (Homarus americanus). In another study, it was reported that dusting of Norwegian lobster (Nephrops
norvegicus) with sulphides delayed the formation of melanosis in the chilled storage
for at least 7 days (Martínez-Alvarez et al. 2007, 2008b). The combination of
organic acids and chelating agents and 4-hexyresorcinol was found to inhibit the
PPO activity of Norwegian lobster (Nephrops norvegicus) (Lopez-Caballero
et al. 2006).
In addition to being valuable and delicious, lobsters are products that can easily
undergo quality changes and therefore easily perish. Biogenic amines can be formed
2 Crustacean Shellfish
undergo autoxidation and polymerization to form dark pigments. PPO is responsible for the sclerotization (hardening) of the exoskeleton after moulting. Cuticle
hardening occurs when the quinones produced from diphenol oxidation form crosslinks between adjacent protein chains (Stevenson 1985). Factors affecting blackspot
in shrimps and lobsters include method of capture, catch handling, age, and sex.
polyphenoloxidase (PPO) activity was measured in cuticles of Norwegian lobsters
caught over a 7-month period. It was observed that PPO activity increased in early
August and early October, but the high PPO activity detected in May showed the
spring moulting period. Exposure to damage and stress of Norwegian lobsters was
associated with an increase in PPO activity. No correlation was observed between
initial PPO activity and black spot development during the storage of Norwegian
lobsters. This showed that biochemical events during storage were more than the
initial PPO level for black spot development. The times during the year during
which the Norway lobsters are more likely to moult are dependent on sex and maturity, but also differ from region to region. On reaching sexual maturity, male Norway
lobsters moult twice a year until they are 6–7 years old, whereas females moult
once, or not at all, in a given year. Longer trawl hauls and rough handling on board
would lead to the loss of claws, whereas, conversely, short hauls and gentle handling
of the catch on board would preserve more Norway lobsters intact. Thus, missing
claws reflect rough treatment of the Norway lobsters both during and after the haul.
A linear correlation was found between the number of remaining claws on the
Norway lobsters and PPO activity. This suggests that rough handling of the Norway
lobster catch is associated with an increase in PPO activity in the lobsters (Bartolo
and Birk 2002).
Melanosis has been reported to occur due to the presence of high levels of polyphenoloxidase (PPO) in cephalotorax of lobsters (Martínez-Alvarez et al. 2008b).
Rough handling of lobsters and other traumatic events trigger the defence mechanism of these organisms having PPO activity, resulting in increased blackening.
Even when they are alive, they can be encouraged to develop melanosis because of
any injury (Ogawa et al. 1984). The blackening of the broken clamped legs, parapods and carapax is caused by hemocyanin from PPO (Gimenez et al. 2010).
Inhibition of melanosis catalyzed by polyphenoloxidases is inhibited by bisulphites
by reaction with quinones forming sulphoquinones (Ferrer et al. 1989).
In various studies, different inhibitors were used for inhibition of melanosis in
lobsters and positive results were obtained. Brack et al. (2008) found that Mimosine
inhibits monophenol and diphenoloxidase activity of European spiny lobster
(Palinurus elephas). Opoku-Gyamfua et al. (1992) reported inhibition effect of
EDTA (ethylenediamine tetra acetic acid) on PPO from lobster (Homarus americanus). In another study, it was reported that dusting of Norwegian lobster (Nephrops
norvegicus) with sulphides delayed the formation of melanosis in the chilled storage
for at least 7 days (Martínez-Alvarez et al. 2007, 2008b). The combination of
organic acids and chelating agents and 4-hexyresorcinol was found to inhibit the
PPO activity of Norwegian lobster (Nephrops norvegicus) (Lopez-Caballero
et al. 2006).
In addition to being valuable and delicious, lobsters are products that can easily
undergo quality changes and therefore easily perish. Biogenic amines can be formed
2 Crustacean Shellfish