Q How does frozen salmon lose its pinkish colour?
A What you are observing may be temporary colour loss because of light scattering by ice crystals.
Researchers in Norway have used microscopy to study the size of ice crystals in frozen salmon at varying temperatures.
The study measured the size of the voids in cell tissue left by the ice crystals. The freezing temperatures thought best to ensure quality caused a substantial loss in colour, the researchers found.
The temperatures left many small ice crystals in the flesh of the fish, which increased the scattering of light and the absorption of visible wavelengths.
Most of the coloration in pinkish fish comes from astaxanthin, a red, fat-soluble carotenoid.
Normal levels were still present in properly frozen fish, the scientists found. The colour loss is temporary.
The researchers said their methods could be used to distinguish between temporary colour loss and the washed-out appearance of truly bad fish.