Sit down and brace yourself, for we have disturbing news. Blueberries – the fruits that dedicate 36-44 percent of their name to telling you they are blue – don't actually contain any blue pigment.
"Blueberries are observably blue; however, the pigments found in blueberries are not," as a team from the University of Bristol put it in a new study. "The color variation of blueberries does not predominantly depend on pigmentation. The anthocyanins, contained in high concentrations in these fruits, generally have dark red scattering profiles."
Simply put, you would not be able to extract that nice blue color through normal methods.
"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," Rox Middleton, research fellow at Bristol’s School of Biological Sciences, explained in a statement. "That was why we knew that there must be something strange about the colour."
Taking a closer look, the team found that the answer lay in the thin layer of wax that coats blueberries. Removing this layer – just two microns thick – and then recrystallizing it, they found it was made of miniature structures that scatter blue and UV light. Rather than appearing blue because of blue pigments within the fruit, it appears blue (and blue/UV to birds) because of the way light interacts with the randomly arranged crystal structures of the wax, according to the researchers.
Most plants have a wax covering, but its prominent role in the coloration of blue fruit was unknown until now. The team hopes to find easier methods of recreating the coating.
“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," Middleton added.
“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."
The study is published in Science Advances.