A recent study published in Science Advances sheds some (blue) light on why blueberries are blue—and the advantages of a futuristic edible blue paint.
There are small “structures” on the wax on the outside of a blueberry that gives it its blue colouring, according to the researchers at the University of Bristol, and authors of the paper. This applies to many other fruits that are the same colour (damsons, sloes, and juniper berries).
When you picture yourself biting into a forkful of blueberry pie or maybe a fresh buttery blueberry muffin, you can see that the inside pigmentation of the berry is actually dark red.
The blue comes from the layer of wax surrounding the berry, which is made of tiny structures that actually scatter blue and UV light. “This gives blueberries their blue appearance to humans and blue-UV to birds. The chromatic blue-UV reflectance arises from the interaction of the randomly arranged crystal structures of the epicuticular wax with light,” according to a press release from Bristol University.
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Rox Middleton, a research fellow at Bristol’s School of Biological Sciences, explains in the release: “The blue of blueberries can’t be ‘extracted’ by squishing—because it isn’t located in the pigmented juice that can be squeezed from the fruit. That was why we knew that there must be something strange about the colour.”
Strange glaze indeed—Middleton notes that when the researchers removed the wax coating and “re-crystalised it on a card” they were able to recreate blue-UV coating. The ultra-thin coating created is about two microns thick. Although it is less reflective, it’s visibly blue and also reflects UV light well. “It shows that nature has evolved to use a really neat trick, an ultrathin layer for an important colorant,” says Middleton.
Many plants naturally have a wax coating, which the researchers indicated is effective as a hydrophobic, self-cleaning function. What they did not understand was the wax’s importance for showing coloration.
Do humans dream of edible paint? Seems like the group feels there’s merit in further research—the team plans to look at improved ways of creating the coating for various applications, including edible UV and blue-reflective paint.
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“It was really interesting to find that there was an unknown coloration mechanism right under our noses, on popular fruits that we grow and eat all the time,” explains Middleton in the recent research announcement. “It was even more exciting to be able to reproduce that colour by harvesting the wax to make a new blue coating that no one’s seen before. Building all that functionality of this natural wax into artificially engineered materials is the dream!”
We can imagine it now: disclaimers that a blueberry-blue paint is delicious! Ordinary blue paint from the paint store? Not so much.
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