Greg, I am looking at a similar reaction in western rock lobster blood (Western Australia). We have found that the reaction is due to polyphenoloxidase enzymes found in the haemolymph. If the haemolymph is heated using an adequate temperature-time combination the reaction can be stopped as the protein structure of the enzyme becomes denatured. (H. Williams, J. Mamo and G. W. Davidson 2003. Heat-induced activation of polyphenoloxidase in western rock lobster (Panulirus cygnus) haemolymph: Implications for heat processing, J Food Sci, 68 (6): 1928-1932) We have also noted that many factors such as moult stage will impact on the level of PPO in the haemolymph in live lobsters but the effects of cooking temperature and time are more important than PPO level in determining whether or not the haemolymph will change colour during processing. (H. Williams, G. W. Davidson and J. Mamo 2005. "FRDC Final report: Striking a balance between melanosis and weight recovery in western rock lobster (Panulirus cygnus)" Rpt: 2001/235, Fisheries Research and Development Corporation, Canberra)
Babbitt also pointed out that when picking crab meat, washing it thoroughly and precooking to 60C before canning reduced the incidence of bluing (J. K. Babbitt, D. K. Law and D. L. Crawford 1973. Blueing discolouration in canned crab meat (Cancer magister), J Food Sci, 38 1101- 1103)
hope these comments help
Hannah Williams
Phone 08 9266 3329 MB: 0416123424 Fax: 08 9266 2958
Nutrition and Food Science Research Centre
Building 400 Room 361
School of Public Health
Curtin University of Technology
GPO Box U1987
Perth
Western Australia 6845
"Life is what happens while you are making other plans" ~ John Lennon
________________________________
From: owner-seafood@ucdavis.edu [mailto:owner-seafood@ucdavis.edu] On Behalf Of Gregg Morrow
Sent: Friday, 19 May 2006 9:58 PM
To: seafood@ucdavis.edu
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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