howgate (phowgate@rsc.co.uk)
Sun, 23 Jan 2000 21:36:17 -0000
Andrew
On 21 January you showed two pictures of haddock, one discoloured. I assume
you were referring to the bright yellow fillet.
Carotenoids can be taken up from the diet of animals and can colour the
flesh. A common example, in the USA at least, is the yellow colour of
corn-fed chickens. I assume this is due to the carotenoid, zeaxanthin, that
imparts the yellow colour to corn. Nearer to home, the pink colour of
salmon, in the wild, is due predominately to the carotenoid astaxanthin,
and other carotenoids in minor amounts, from crustacea in the diet. I can
only write from experience of haddock landed in Britain. I have come
across light pink colouration in haddock, and in cod, which is assumed to
come from crustacea in the diet, but I have not come across the yellow
colour shown in your picture. A number of carotenoids other than the pink
astaxanthin and canthaxanthin are found in marine animals. Polychaete worms
are sources of a variety of carotenoids and, as I recollect, are described
in: Simpson K.L. Katayama T. Chichester C.O., 1981, Carotenoids in fish
feeds. In: Carotenoids as Colorants and Vitamin A Precursors, J.C.
Bauernfeind, ed., Academic press, New York, pp 463-534. I write 'recollect'
because I do not have a copy of this chapter, but I consulted the book in
one of the academic libraries in Aberdeen and I no longer live in that
city). Chemical analysis - not too difficult - will be able to identify if
the colour is a carotenoid, and its nature.
Let me put forward as a hypothesis that the haddock in question have been
feeding on polychaete worms that contain a yellow carotenoid. If you know
the catching ground of the haddock, you might be able to confirm from a
marine laboratory if polychaete worms are likely to be an item of the
haddock diet. Unless they had been feeding on corn!
Given the known free-radical scavenging properties of carotenoids, and the
benefits to health of carotenoids in the diet, the yellow colour should
perhaps be seen as a benefit, not a defect.
Peter Howgate
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