25
derivatives, and phenolic compounds such as coumarins. In recent years, interest
has been focused on natural antioxidants due to the toxicity of synthetic antioxidants. Natural antioxidants are the ingredients that people have consumed for hundreds of years or mixed into foods. Therefore, it is seen as safe by consumers.
Fruits, vegetables, cereals, teas, wines, and some spices are natural antioxidant
sources (Buricova and Reblova 2008). Natural antioxidants are primarily plant phenolics, which occur in all parts of plants such as fruits, vegetables, seeds, leaves,
nuts (nuts, walnuts), roots and shells. Plant phenolics serve as reducing agent, free
radical scavenger, metal chelating agent and singlet oxygen scavenger (Jayathilakan
et al. 2007). In a study investigating the effect of natural antioxidants on melanosis
in shrimps, it has been found that the extract of the grape seed is effective in delaying the melanosis in the shrimp for a short time (Gokoglu and Yerlikaya 2008).
Green tea and rosemary extracts were found effective to delay melanosis in shrimp
(Aristerus antennatus) (Yatmaz and Gokoglu 2016). Nirmal and Benjakul (2009a)
also reported that green tea extract prevented melanosis. The extract obtained from
edible enokitake mushroom tried as melanosis inhibiting agent and was found to be
successful (Jang et al. 2003).
Chelating and Complexing Agents
Enzymes generally have metal ions in their active parts. Removal of these ions with
chelating agents may inactivate the enzyme. Chelating agents can form compounds
via non-dispersive electron pairs in their molecular structure by pro-oxidative agents
such as copper and iron ions (Kim et al. 2000). The chelators used in the food industry include sorbic acid, polycarboxylic acids (citric, malic, tartaric, and succinic
acids), polyphosphates (ATP and pyrophosphates), macromolecules (proteins) and
EDTA (Ethylenediaminetetraacetate). It is stated that the enzyme activity of PPO,
which needs copper ions for its activation, can be prevented or reduced by chelating
agents or by the formation of compounds. Kojic acid are reported as a potential
antimelanotic agent (Chen et al. 1991). Kojic acid was found to inhibit PPO activity
in shrimp (Benjakul et al. 2006).
Acidulants
Acids are generally used to maintain the optimum pH for the catalytic activity of the
enzyme. Polyphenoloxidase enzyme is inactivated by decreasing pH. Acids are
often used in combination with other antimelanotic agents (Gomez-Guillen et al.
2005). Acidifiers, such as citric, malic, and ascorbic acids, can lower the pH of a
system, and thus may inactivate PPO (Montero et al. 2001a).
Citric acid is one of the acidifiers commonly used in the food industry. The citric
acid has inhibitory effect on melanosis by lowering the pH as well as chelation of
copper in the active part of the enzyme. However, it has no antimelanotic effect
alone. Citric acid is often used in combination with other agents used to prevent
melanosis. Combination of l-lactic acid and 4-hexylresorcinol in brown shrimp
(Penaeus aztecus) has been reported to be effective in preventing melanosis (Benner
2.1 Shrimps/Prawns
derivatives, and phenolic compounds such as coumarins. In recent years, interest
has been focused on natural antioxidants due to the toxicity of synthetic antioxidants. Natural antioxidants are the ingredients that people have consumed for hundreds of years or mixed into foods. Therefore, it is seen as safe by consumers.
Fruits, vegetables, cereals, teas, wines, and some spices are natural antioxidant
sources (Buricova and Reblova 2008). Natural antioxidants are primarily plant phenolics, which occur in all parts of plants such as fruits, vegetables, seeds, leaves,
nuts (nuts, walnuts), roots and shells. Plant phenolics serve as reducing agent, free
radical scavenger, metal chelating agent and singlet oxygen scavenger (Jayathilakan
et al. 2007). In a study investigating the effect of natural antioxidants on melanosis
in shrimps, it has been found that the extract of the grape seed is effective in delaying the melanosis in the shrimp for a short time (Gokoglu and Yerlikaya 2008).
Green tea and rosemary extracts were found effective to delay melanosis in shrimp
(Aristerus antennatus) (Yatmaz and Gokoglu 2016). Nirmal and Benjakul (2009a)
also reported that green tea extract prevented melanosis. The extract obtained from
edible enokitake mushroom tried as melanosis inhibiting agent and was found to be
successful (Jang et al. 2003).
Chelating and Complexing Agents
Enzymes generally have metal ions in their active parts. Removal of these ions with
chelating agents may inactivate the enzyme. Chelating agents can form compounds
via non-dispersive electron pairs in their molecular structure by pro-oxidative agents
such as copper and iron ions (Kim et al. 2000). The chelators used in the food industry include sorbic acid, polycarboxylic acids (citric, malic, tartaric, and succinic
acids), polyphosphates (ATP and pyrophosphates), macromolecules (proteins) and
EDTA (Ethylenediaminetetraacetate). It is stated that the enzyme activity of PPO,
which needs copper ions for its activation, can be prevented or reduced by chelating
agents or by the formation of compounds. Kojic acid are reported as a potential
antimelanotic agent (Chen et al. 1991). Kojic acid was found to inhibit PPO activity
in shrimp (Benjakul et al. 2006).
Acidulants
Acids are generally used to maintain the optimum pH for the catalytic activity of the
enzyme. Polyphenoloxidase enzyme is inactivated by decreasing pH. Acids are
often used in combination with other antimelanotic agents (Gomez-Guillen et al.
2005). Acidifiers, such as citric, malic, and ascorbic acids, can lower the pH of a
system, and thus may inactivate PPO (Montero et al. 2001a).
Citric acid is one of the acidifiers commonly used in the food industry. The citric
acid has inhibitory effect on melanosis by lowering the pH as well as chelation of
copper in the active part of the enzyme. However, it has no antimelanotic effect
alone. Citric acid is often used in combination with other agents used to prevent
melanosis. Combination of l-lactic acid and 4-hexylresorcinol in brown shrimp
(Penaeus aztecus) has been reported to be effective in preventing melanosis (Benner
2.1 Shrimps/Prawns