Credit: Rox Middleton
Key points:
- The blue color of blueberries results from a layer of wax that surrounds the fruit.
- The wax layer comprises miniature structures that scatter blue- and UV-light to give the fruit a blue appearance to humans and a blue-UV appearance to birds.
- The research team removed the wax and re-crystallized it on a card to create a new blue-UV coating that may be used as a sustainable, biocompatible and edible UV and blue-reflective paint.
New research, published in Science Advances, reveals why blueberries are blue despite the dark red color of the pigment in their skin. The findings apply to many fruits that are the same color, including damsons, sloes, and juniper berries.
Researchers determined the blue color results from a layer of wax that surround the fruit. This layer comprises miniature structures that scatter blue and UV light to give the berries a blue appearance to humans and a blue-UV appearance to birds. The chromatic blue-UV reflectance arises from the interaction of randomly arranged crystal structures of the epicuticular wax with light.
Next, the research team removed the wax and re-crystallized it on a card to create a new blue-UV coating. The ultra-thin colorant they constructed was approximately two microns thick, visibly blue, and reflected UV.
“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,” said first author Rox Middleton, research fellow at University of Bristow.
In the future, the researchers plan to develop easier methods to recreate the wax coating and to apply it in multiple contexts. One possibility is to use the coating to protect plants much like its natural biological function. They also hope to create a sustainable, biocompatible, and edible UV and blue-reflective paint.