Complaint Casebook Decoloration of Crab

When I tried to eat crabs, I was black.

Photograph of crab (whole)

• Appearance: The inside of the shell is also black. The meat on the feet is fresh.
• ｐＨ： 8.1
• Smell: No decay odor
• Volatile base nitrogen (*): 18mg%

（※） Volatile base nitrogen…When the freshness of food such as seafood decreases, ammonia and amine are produced. Nitrogen-containing compounds produced by this transformation are called volatile base nitrogen. This volatile nitrogen is considered to be one of the indicators for determining freshness, and is considered to be an initial rot when it reaches 30 mg per 100 g of specimens.

The actual product is black as if it were covered with heavy oil, but it did not smell heavy oil. This phenomenon is thought to have produced melanin by oxidizing the tyrosine contained in crab meat by the action of oxidative enzyme tyrosiegenase. Crabs may turn black in about 3 hours after landing. This melanin is a black pigment component such as skin, retina, and hair.

Melanin: It is a brown or purple polymer pigment that is biosynthesized by the enzymatic and non-fermental oxidation, decarboxylic, and coupling reaction of phenols, whose exact composition is unknown. It is widely found in flora and fauna, including humans and hair crabs, and is thought to help absorb excessive light in the body, but its other roles are unknown. It is a substance that usually binds firmly to proteins and dissolves in warm concentrated sulfuric acid and alkali, but is insoluble in water and organic solvents, and is extremely difficult to handle. Tyrosine, an aromatic amino acid, is considered to be the most common biosynthesis precursor, and it is said that the melanin generation pathways go through dopa, dopaquinone, and door quinone.

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Published on March 8, 2007