19
Nucleotide Degradation
Adenosine-5′-triphosphate (ATP) is available in muscle of shrimp in postmortem
period acts as an energy source for muscle contraction. During storage, adenosine
diphosphate (ADP) forms by depleting of ATP via endogenous enzymes. Adenosine
triphosphate (ATP) degrades to adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP), Inosine (Ino) and hypoxanthine
(Hx). Hypoxanthine is a quality indicator in cold storage and is characterized by
bitter taste in the product (Huss 1995). Creatine phosphate is a reservoir of energyrich phosphate in the muscle cells and ATP is formed by the reaction between creatine phosphate and ADP in the live organism. After depletion of creatine phosphate,
ATP is produced from ADP via phosphorylation. When regeneration is over after
death, ATP rapidly degrades, and rigor-mortis develops (Huss 1988).
Enzymatic Browning
After catching/harvesting, colour changes occur in the shell segments of shrimp,
especially at the place where the head part is removed, by the effect of environmental factors (sun, temperature, etc.). In this formation, as well as environmental factors, the late removing of the head after in harvesting, the application of no or
insufficient cooling accelerates the colour change. This colour change is called
“melanosis”, “darkening”, “browning” and “black spot” (Erkan et al. 2007). Shortly
after catching, darkening is the main problem of those dealing with shrimp trade.
This darkening is one of the industry’s biggest problems, because the negative
changes occur in the sensory characteristics of shellfish creatures. It results in
shorter shelf life and lower product quality, thus reducing the acceptability of consumers and thus causing financial losses (Kim et al. 2000; Nirmal and Benjakul
2009a). The melanosis event in crustaceans is often seen before the onset of deterioration during storage after death. It is reported that melanosis begins within a few
hours after catching. Especially in autumn and winter, they are more sensitive due
to moulting and nutritional deficiencies (Montero et al. 2004). This change has a
significant effect on quality and is caused by enzymatic degradation due to the effect
of oxygen and light in air. Melanosis develops very rapidly in shrimps stored in cold
without any preservatives and can lose its market value within 24 h (Rotllant et al.
2002). Melanosis is a biochemical process and occurs by the enzyme polyphenoloxidase. In living crustaceans polyphenoloxidase enzyme is stored as proenzyme in
the blood and lymphas and in the cuticle (epiderm). Stimulation of the immune
system, the scarification of the cuticle and the process of wound healing is responsible for activation of the enzyme polyphenoloxidase (Martínez-Alvarez et al.
2005a, 2008a). After harvest and death, PPO systems are still active and can promote the development of black pigments around the shell and on the meat surface
(Thepnuan 2007). The enzymatic browning reaction is a reaction that catalyses the
phenoloxidase, monophenoloxidase, diphenoloxidase and tyrosinase, called the
polyphenoloxidase enzyme. The phenoloxidase enzyme converts the phenolic
2.1 Shrimps/Prawns
Nucleotide Degradation
Adenosine-5′-triphosphate (ATP) is available in muscle of shrimp in postmortem
period acts as an energy source for muscle contraction. During storage, adenosine
diphosphate (ADP) forms by depleting of ATP via endogenous enzymes. Adenosine
triphosphate (ATP) degrades to adenosine diphosphate (ADP), adenosine monophosphate (AMP), inosine monophosphate (IMP), Inosine (Ino) and hypoxanthine
(Hx). Hypoxanthine is a quality indicator in cold storage and is characterized by
bitter taste in the product (Huss 1995). Creatine phosphate is a reservoir of energyrich phosphate in the muscle cells and ATP is formed by the reaction between creatine phosphate and ADP in the live organism. After depletion of creatine phosphate,
ATP is produced from ADP via phosphorylation. When regeneration is over after
death, ATP rapidly degrades, and rigor-mortis develops (Huss 1988).
Enzymatic Browning
After catching/harvesting, colour changes occur in the shell segments of shrimp,
especially at the place where the head part is removed, by the effect of environmental factors (sun, temperature, etc.). In this formation, as well as environmental factors, the late removing of the head after in harvesting, the application of no or
insufficient cooling accelerates the colour change. This colour change is called
“melanosis”, “darkening”, “browning” and “black spot” (Erkan et al. 2007). Shortly
after catching, darkening is the main problem of those dealing with shrimp trade.
This darkening is one of the industry’s biggest problems, because the negative
changes occur in the sensory characteristics of shellfish creatures. It results in
shorter shelf life and lower product quality, thus reducing the acceptability of consumers and thus causing financial losses (Kim et al. 2000; Nirmal and Benjakul
2009a). The melanosis event in crustaceans is often seen before the onset of deterioration during storage after death. It is reported that melanosis begins within a few
hours after catching. Especially in autumn and winter, they are more sensitive due
to moulting and nutritional deficiencies (Montero et al. 2004). This change has a
significant effect on quality and is caused by enzymatic degradation due to the effect
of oxygen and light in air. Melanosis develops very rapidly in shrimps stored in cold
without any preservatives and can lose its market value within 24 h (Rotllant et al.
2002). Melanosis is a biochemical process and occurs by the enzyme polyphenoloxidase. In living crustaceans polyphenoloxidase enzyme is stored as proenzyme in
the blood and lymphas and in the cuticle (epiderm). Stimulation of the immune
system, the scarification of the cuticle and the process of wound healing is responsible for activation of the enzyme polyphenoloxidase (Martínez-Alvarez et al.
2005a, 2008a). After harvest and death, PPO systems are still active and can promote the development of black pigments around the shell and on the meat surface
(Thepnuan 2007). The enzymatic browning reaction is a reaction that catalyses the
phenoloxidase, monophenoloxidase, diphenoloxidase and tyrosinase, called the
polyphenoloxidase enzyme. The phenoloxidase enzyme converts the phenolic
2.1 Shrimps/Prawns