The color blue is not very common in animals and plants, in which red, yellow and green predominate, to give three examples. Perhaps because of this uniqueness, in recent years various studies have been carried out on the bluish exceptions of the animal kingdoms (the most recent, a spider) and plants. In the vegetable section, research by experts from the University of Bristol now stands out, which has allowed us to discover why blueberries are externally blue. The results of this curious work have been published in the journal Science Advances (February 7).
Specifically, researchers show why blueberries are blue despite the dark red pigments in the fruit’s skin. Specifically, they indicate in their scientific article, the blue color of these fruits when they are completely ripe is provided by a layer of wax that surrounds the fruit and is formed by miniature structures that disperse blue and ultraviolet light.
This unique optical phenomenon gives blueberries their blue appearance, seen by human eyes, and their ultraviolet blue reflection for the sight of various birds and insects.
“Blue-UV chromatic reflectance arises from the interaction of the randomly arranged crystalline structures of the epicuticular wax with light,” details the University of Bristol.
Rox Middleton, a researcher at Bristol’s School of Biological Sciences, explained that “the blue in blueberries cannot be ‘extracted’ by squeezing one of these berries, because it is not found in the pigmented juice that can be squeezed from the fruit; so we knew there must be something strange about the color.”
“So we removed the wax and recrystallized it onto cardstock, and by doing so, we were able to create a new blue-UV coating.”
The ultra-fine dye is around two microns thick and, although less reflective, is visibly blue and reflects UV rays well, possibly paving the way for new dyeing methods.
“This shows that nature has evolved to use a really clever trick, an ultra-thin layer for an important dye,” added Rox Middleton.
Most plants are covered in a thin layer of wax that has multiple functions, many of them that scientists do not yet understand. They know that it can be very effective as a hydrophobic and self-cleaning coating. However, until now researchers did not know how important this structure was for visible coloration.
Now the team plans to look at easier ways to recreate the coating and apply it. This could lead to a more sustainable, biocompatible and even edible paint that reflects UV rays and blue. Furthermore, these coatings could have the same multiple functions as natural biological ones that protect plants. In fact, a similar effect occurs in other fruits such as the damson plum (Damascus plum) or the juniper.
The lead author of this study details: “It was really interesting to discover that there was an unknown coloration mechanism right under our noses, in popular fruits that we grow and eat all the time.
“It was even more exciting to be able to reproduce that color by collecting the wax to create a new blue layer that no one had seen before. “Building all the functionality of this natural wax into artificially engineered materials is the dream!”
