howgate (phowgate@rsc.co.uk)
Tue, 25 Jan 2000 21:04:46 -0000
Dear Andrew
Thank you for drawing my attention to the paper by Dyer on orange-red
colour in haddock. I must get a copy as the published literature on
discolourations in fish is very sparse. It is interesting to see that Dyer
identified zeaxanthin in the fish. Chemistry textbooks give zeaxanthin as a
typical carotenoid and being responsible for the yellow colour of corn, but
that does not mean it is found only in corn. You are quite right to point
out to Verhoeven, that the yellow colour is a quality defect, though
probably, if it is a carotenoid, harmless, maybe even positively good for
you. Health food stores sell zeaxanthin. Consumers look at yellow
discolouration in chickens as a plus quality attribute, but I think you
would have a hard job persuading consumers that the same type of
colouration in haddock is a plus point. I doubt if algae would be the
source of the pigment. As far as I am aware, haddock, certainly of the size
you are referring to, are carnivores and would not browse on phytoplankton.
I can't explain the apparent increase in intensity of colour during frozen
storage. The perceived pink colour of salmon, particularly when pigmented
with canthaxanthin, is reported to decrease in intensity during frozen
storage, even though the amount of pigment as determined analytically does
not change. Carotenoids will oxidise during frozen storage, but I do not
know enough (anything) of the chemistry of carotenoids to predict if the
oxidised product will be more or less intense that the parent compound.
Peter Howgate
----------
> From: Andrew Strak <abstrak@accesswave.ca>
> To: phowgate@rsc.co.uk; 'Seafood List' <seafood@ucdavis.edu>
> Subject: Re: Haddock Flesh Discolouration
> Date: 24 January 2000 00:54
>
> Peter,
>
> Thank you for your insight. The fish was from the Barents Sea (unknown
exact
> location, though). In the meantime I have come across one old paper by
E.G.
> Bligh and W.J.
> Dyer 'Orange-red Flesh in Cod and Haddock" - J.Fish.Res.Bd. Canada,
16(4),
> 1959 not probably listed in any database anymore. Astaxanthin and
zeaxanthin
> in the proportion of 2:1 were found to be responsible for the
pigmentation
> of the flesh of Cod. Zeaxanthin was the only pigment detected in the
flesh
> of a similarly pigmented haddock. Therefore concerning the carotenoid
> identification you are probably right on the point. What strange is that
the
> colour intensity seems to be increasing with the time in frozen storage.
And
> the incidence of the number of fish affected by the phenomenum in this
case
> is also pretty high (5%), unlike your experience or reported by Blight
and
> Dyer. Apparently there must some cargo ship carrying corn went down
recently
> :-).
>
> Andrew Strak
>
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