none StationeryDear Gregg,
The book Chemistry and Biochemistry of Marine Food Products. R.E. Martin, G.J. Flick, C.E. Hebard, D.R. Ward, eds,Westport, Co. USA: Avi Publishing Co., Inc. has a chapter, Chap 20, pp 423-428, by Babbitt, 'Blueing discoloration of Dungeness crabmeat.' which discusses the chemistry of the process. You ask specifically how to stop it and I copy the last 3 paragraphs from the chapter.
"How then can the blueing discoloration be prevented? Industry, by trial and error, has developed several practices to reduce the incidence of blueing. Only crabs that are alive and in good condition are processed. Crabs that have been held in a cooler (1̊-3̊C) even for up to 4 days are edible if properly cooked. However, the chances of blueing occurring in the cooked crab are greatly increased, particularly if the cooking times and temperatures are not adequate to inactivate the phenolases. Certainly, care must be taken to properly cook the crab, since underprocessing will result in blueing.
Molting is a factor in the blueing reaction, since the phenolic compounds are involved in the formation of the new shell (sclerotization) of the crab. So, during times of molting, extra care must be used in handling and processing crab to prevent blueing.
If the crabmeat is to be thermal-processed, the cooking time and temperatures of the raw crab are not as critical. However, as soon as the crab is cooked, the meat from the shell must be removed and thermal-processed. Regardless of how long the live crab are cooked, any delay in thermal pricessing the crabmeat will result in a higher incidence of blueing. Using frozen crab sections to produce canned crabmeat will also increase the risk of blueing. Whole crab or crab sections should be thoroughly cooked before freezing to reduce the risk of blueing. Finally, avoid any contact of copper or iron with the crab since these metals can greatly intensify the blueing discoloration."
Peter Howgate
----- Original Message -----
From: Gregg Morrow
To: seafood@ucdavis.edu
Sent: Friday, May 19, 2006 2:58 PM
Subject: Bluing King Crab
Hello,
I am looking for a good explanation for what stops bluing in King Crab.
I understand that crab blood gets its blue color from the oxygen-carrying respiratory protein hemocyanin, and that there are a number of theories as to how cooking controls the ability of the blood to turn blue.
I am curious as to how cooking the crab to a certain temperature for a minimum time, stops the bluing process.
Does cooking disrupts the molecular structure of the hemocyanin?
Does cooking destroy or de-activate an oxidative enzyme naturally found in the blood?
Occasionally, we have observed slight amounts of bluing in the external surfaces shoulder and attribute this to improper bleeding and washing during the butchering process. Extensive thaw tests of these crab sections show that the crab is properly cooked and no bluing is found elsewhere within the section. I believe that blood from a freshly butchered section will turn blue when it is exposed to air and that you can not cook the blue away.
I have also observed in crab sections that were purposely undercooked, how the bluing process is slowed by maintaining a deep frozen temperature (colder than 0°F). Portions of this same undercooked crab maintained at warmer temperatures 40°-45°F will show significant signs of bluing (from the shoulder to the dactylus) within a very short period of time. This would seem to support the idea of an oxidative enzyme that has its ability diminished by the cold temperature.
Does the molting cycle of the crab have any factor?
Thank you,
Gregg Morrow
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