A team from the University of Bristol has uncovered the reason behind the characteristic blue color of blueberries, despite the dark red pigment found in their skin. Researchers explained that their findings also shed light on the coloring mechanisms of various other fruits, including prunes, sloe berries, and juniper. According to the data obtained, the blue hue of blueberries is attributed to tiny structures in the waxy coating of the berries.
As reported by the Independent, the color results from the interaction of chaotically arranged crystalline structures in the waxy coating with light. Despite the dark red pigment in the skin of blueberries, it is the wax layer surrounding the fruit that gives it its blue appearance. This layer consists of miniature structures that scatter blue and ultraviolet light. Researchers noted that this is why the fruit appears blue to humans and some birds.
“The blue color of blueberries cannot be ‘extracted’ by crushing them, as it is not present in the pigmented juice that can be squeezed from the fruit. That’s why we suspected there was something unusual about this color,” said Dr. Rox Middleton, a research fellow at the Bristol School of Biological Sciences. To investigate further, the scientists removed the wax and recrystallized it on cardboard, creating an entirely new blue UV coating in the process. They expressed that incorporating all the functionality of this natural wax into artificially created materials is a dream.
“It was truly fascinating to discover an unknown coloring mechanism right under our noses in popular fruits that we grow and consume regularly. Even more exciting was reproducing this color by collecting the wax and creating a new blue coating that no one had seen before,” Dr. Middleton commented on the experiment’s results. This colored layer is extremely thin—about two microns thick. It exhibits a noticeable blue color and effectively reflects UV radiation, potentially paving the way for new dyeing methods.
As Dr. Middleton pointed out, this indicates that nature has learned to use a truly clever trick: an ultrathin layer for an important dye. Most plants are covered with a thin layer of wax that serves multiple functions, many of which scientists still cannot explain. These coatings, for example, can be very effective for self-cleaning and retaining water. Until recently, the team was unaware of how crucial the structure of the coating is for the visible coloring of berries. Now, researchers plan to explore ways to reproduce the coating and apply it, which could lead to the creation of a more sustainable, biocompatible, and even edible paint that reflects ultraviolet and blue light. The findings of this research were published in Science Advances.