Scientists reveal why blueberries are blue

Researchers at the University of Bristol have revealed that tiny external structures in the wax coating of blueberries give them their blue color. This is true for many fruits of the same color, such as damsons, sloes, and juniper berries.

In a study published in scientific progress, researchers showed why blueberries are blue despite the dark red pigment in their skins. The blue color of the fruit is provided by a layer of wax that surrounds the fruit, which is made up of small structures that scatter blue light and ultraviolet light. This makes blueberries appear blue to humans and provides blue ultraviolet light to birds. The chromatic blue-UV reflectance results from the interaction of light with the randomly arranged crystal structure of epicuticular wax.

Rox Middleton, a researcher in the School of Biological Sciences at the University of Bristol, said: ‘The blue color of blueberries cannot be ‘extracted’ by crushing them, as they are not contained in the pigmented juice that can be squeezed out of the fruit. Yes, that’s why.” We knew there must be something strange about that color.

“So we removed the wax and recrystallized it on the card. In doing so, we were able to create a completely new blue UV coating.”

This ultra-thin colorant is about 2 microns thick, has a low reflectance, but is visibly blue and reflects UV well, potentially paving the way for new colorant methods.

“This shows that nature has evolved to use a very clever trick: an extremely thin layer of a vital colorant,” Rox added.

Most plants are covered with a thin layer of wax, which has multiple functions, many of which are still unknown to scientists. They know that it is highly effective as a hydrophobic, self-cleaning coating, but only now have they realized how important this structure is for visible coloration.

The team now plans to look at easier ways to recreate and apply the coating. This could lead to the development of more sustainable, biocompatible, and even edible UV- and blue-reflecting paints.

Additionally, these coatings may have multiple functions similar to natural biological coatings that protect plants.

Rox continued, “It was very interesting to discover that there is an unknown coloring mechanism so close to the popular fruit that we grow and eat all the time.

“It was even more exciting to be able to recreate that color by taking wax and creating a new blue coating that no one had ever seen before.

“Our dream is to incorporate all the functionality of this natural wax into a man-made material.”