Nature|The surface color is created in the same way as the blue of the sky.
The summary is made by artificial intelligence and checked by a human.
The blue color of the blueberry is due to the structure of its wax layer, not the pigment.
The wax layer reflects blue and ultraviolet wavelengths.
The blue color attracts birds and mammals.
Blue pigments are rare in nature because their production requires a lot of energy.
Like every blueberry picker can see from their hands and maybe even their clothes, blueberry dyes are red. Still, the surface of the berry looks blue.
The blueness is really just the surface, researchers from Britain, Germany and Finland confirm. The color is not due to pigment, but to the play of light in the structures of the wax layer covering the blueberry skin.
If the wax is rubbed off, the rind of the blueberry can appear almost black because its dark red pigments absorb light so strongly.
The same red anthocyanins color the blueberry flesh. As with dyes in general, their hue depends on the proportion of light wavelengths they let escape.
Instead, structural colors are formed when some repeating, very small structures reflect different wavelengths of light in different ways. This is how the blueberry wax layer behaves.
The layer consists of tiny wax particles that most widely reflect the blue and ultraviolet wavelengths of light, the researchers say In Science Advances.
Similarly, blue and ultraviolet wavelengths are also scattered from sunlight when it hits atmospheric particles. The blue of the blueberry is therefore similar to the blue of the sky.
I’m ripe the visibility of blueberry blueness is promoted by the darkness of the rind under the wax layer, the researchers noticed.
The anthocyanins that produce the darkness contribute to making the blueberry attractively nutritious, but without the blueness of the wax, herbivores would not find the berries so easily.
The blueberry wants to be found, because when its berries are swallowed by birds and mammals, the seeds can pass intact through the intestines and, when pooped, reach new places of growth.
Although blue is a good attractor, it is quite rare as a dye in nature. Perhaps it is due to the difficulty of building blue pigments, the researchers speculate. They are large molecules that require a lot of energy to produce.
As structural colors, blue is more common. They are also formed in the waxy surface of, for example, plums and juniper berries.
The wax surface is clever anyway, because it slips off dirt and raindrops and shields many insect pests and pathogens.
Published in Science in Nature 5/2024
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