What you are describing is the "greening" phenomenon that has been
extensively written about in the Japanese literature and some research in
the United State (about 10 to 20 years ago). I have seen photos of greened
tuna loins (albacore) that were a bright green. This sometimes shows up
after the pre-cook, but sometimes shows up after the final retort. For the
consumer who opens a can, this discoloration can be quite alarming, or at
least unsettling. This appears to be only a visual defect that renders some
tuna unsightly, thereby commanding a lower price. It does not, at least to
current knowledge, present any health hazard to consumers of the fish.
Nevertheless, it is considered a defect.
Basically this is a reaction between fish hemoglobin and trimethylamine
oxide present in the tissues. This involves the iron in the heme and its
oxidation state forming a complex with the nitrogen of the TMAO. The
presence of greening does not necessarily imply anything about the handling
of the fish, i.e., in terms of microbiological safety or the addition of
some chemical additives. It has to do with the native concentration of TMAO
and tuna blood.
You should search the food chemical literature and look under "greening"
reactions.
John C. Wekell, Ph.D.
NMFS-Seattle
ph. (206) 860-3388
fax (206) 860-3335
http://www.nwfsc.noaa.gov/hab/
-----Original Message-----
From: owner-seafood@ucdavis.edu [mailto:owner-seafood@ucdavis.edu]On
Behalf Of Binoy E.B
Sent: Friday, October 12, 2001 10:27 AM
To: seafood@ucdavis.edu
Subject: Green tint in Tuna
Dear Group,
Could you please advise me the reason for the
develpment of green tint in Frozen Yellowfin Tuna
Loins on prolonged cold storage since we have observed
this problem after keeping 5 month cold storage along
with dehydration and yellowing.
An immediate response is highly appreciated.
Kind regards
Binoy.
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This archive was generated by hypermail 2b29 : Mon Oct 15 2001 - 13:07:52 PDT