One of a family of yellow, orange and red pigments made by plants and algae: the colour of carrots, tomatoes, peppers, egg yolk, salmon and autumn leaves.
Fat-soluble pigments built on a long chain of alternating single and double bonds, which absorbs blue and violet light. The longer the conjugated chain, the redder the pigment. They are degraded mainly by oxygen, light and prolonged heat.
Animals cannot make carotenoids. The pink of salmon and flamingos and the red of a cooked lobster all come from carotenoids in the diet.
β-carotene makes carrots orange, lycopene makes tomatoes red and lutein makes egg yolk yellow.
Carotenoids are the food colours that survive cooking, and several are authorised colourants in their own right.
Carotenoids are measured in an extract by absorbance. They absorb blue and violet light, so a solvent extract is read with a spectrophotometer at a wavelength in that region and the figure is scaled to the weight of the sample. Paprika's trade colour value is exactly this: the ASTA method reads an acetone extract at 460 nm in a 1 cm cell. Individual carotenoids are separated and quantified by chromatography when the total is not enough. The link to colour is structural: the longer the run of alternating double bonds in the molecule, the further the absorption moves towards longer wavelengths and the redder the pigment.
Paprika, dried apricots or a carotene-coloured drink are stored in clear packaging under shop lighting.
Oxygen and light break the chain of double bonds and the colour fades. Opaque or tinted packaging and limited headspace are how producers protect it.
A buyer assumes that deeper colour means more pigment.
In one study paprika samples differing by about 30% in total carotenoid showed no corresponding difference in ASTA colour units. Extractable colour is a trade measure of appearance, not an assay of content.