To Seafood HACCP Discussion List:
You may want to consider and test for malachite green (MG) and leucomalachite green (LMG) as a source of the coloration. MG is an effective topical fungicide used by the aquaculture industry. MG and the metabolite, leucomalachite green are suspected mutagens. For this reason, MG is NOT APPROVED as an aquaculture veterinary drug in many countries including the United States, Canada and the European Union.
Drug and chemical residue methodology for malachite green and leucomalchite green are featured on the US Food and Drug Administration's "Seafood Information and Resources" web site: http://www.cfsan.fda.gov/seafood1.html .
(Note: analytical methods for flouroquinolones, Nitrofuran and Chloramphenicol are also posted at this site.)
A publication on greening of catfish by MG was written years ago by two scientists at Mississippi State University:
"Absorption of Malachite Green by Channel Catfish" by William E. Poe and Robert P. Wilson (Mississippi Agriculture and Forestry Experiment Station Publication Number 5303), printed in Prog. Fish-Cult. 45(4) October 1983, P. 228-229.
Poe and Wilson cited a publication (by Werth, V.G. and A. Boiteux. 1968. Zur biologischen wirkung von malachitgrün. 6. Mitteilung: die entgiftung des malachitgrün im organismus durch die bildung von leucomalachitgrün. Arzneimittel Forschung 18(1):39-42.) and noted that MG is detoxified in rats to a colorless, nontoxic fat soluble, reduced form called LMG. Subsequent injection of peroxide enzyme oxidized the LMG back to the toxic MG. Poe and Wilson noted that by assuming a similar detoxification mechanism in the catfish, this mechanism could explain the observations in their study: "MG is apparently absorbed into the fish by the gills or through the skin, detoxified to the colorless LMG, and stored in the fat. Subsequent to freezing and storage the LMG is slowly oxidized to MG on the surface of the frozen tissue." The publication results showed that treated catfish abosrb MG and retain it in their tissues and indicate that ample time must be allowed for residues to be eliminated." The green color was only observed in frozen fish after prolonged storage. The earliest appearance of green color was at 13 days in the visceral fat and the longest appearance was 60 days in the muscle of treated catfish that was frozen in a chest-type freezer. The storage temperature is not indicated in the publication.
Pamela Tom
University of California
Sea Grant Extension Program
________________________________
From: owner-seafood@ucdavis.edu [mailto:owner-seafood@ucdavis.edu] On Behalf Of Janani Tulasendrapuram
Sent: Monday, January 08, 2007 12:45 PM
To: seafood@ucdavis.edu
Subject: Farmed Tilapia Discoloration
Hello everyone,
I was wondering if it is possible for farmed tilapia to have green coloration without any off-odors or flavors or any other signs of decomposition. Are there any enzymatic reactions that could trigger this coloration? Or is this a sign of decomposition?
Thanks and Best wishes for the upcoming year!!!
Janani
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