Scientists Unravel the Mystery Behind the Blue Color of Blueberries

The University of Bristol has released a study, revealing that the blue hue of blueberries originates from minute structures embedded in their wax coating, and not from the fruit skin's pigments. This opportunity opens doors for the development of sustainable and biocompatible colorants and coatings influenced by nature.

The research team at the University of Bristol found that minuscule structures inherent in blueberries' wax coating cause their blue coloration.

This finding is applicable to many similarly colored fruits, such as damsons, sloes, and juniper berries.

The study, unveiled in Science Advances, demonstrated why blueberries are blue, despite the deep red pigments present in their skin. Their blue hue is attributed to a wax layer surrounding the fruit. This wax contains tiny structures that reflect blue and UV light, giving blueberries their blue and blue-UV appearance to humans and birds, respectively. Interaction between sunlight and the randomly positioned crystal structures in the epicuticular wax results in the chromatic blue-UV reflectance.

Rox Middleton, a Research Fellow at the School of Biological Sciences at Bristol, clarified: “The blue color of blueberries cannot be obtained by 'extraction' - as it does not reside in the pigmented juice that can be pressed from the fruit. This fact motivated us to believe there was something extraordinary about the color.”

“We eliminated the wax and re-crystallized it on a card, and we managed to formulate a novel blue-UV coating as a result," stated Rox.

The ultra-slim colorant measures approximately two microns in thickness. Its reflectivity is lower, but it is noticeably blue and efficiently reflects UV, arguably bringing about novel colorant methodologies.

Illustration demonstrating light reflection by wax structure. Rox Middleton provides the credit.

Rox further added, “This reveals that evolution in nature incorporates a clever ploy - a highly thin layer for a significant colorant."

Many scientists remain in the dark about the multiple functionalities of the thin wax layer that coats most plants. They are aware that it serves as a superb hydrophobic, self-cleaning cover. However, they have just recognized the structure's importance for visible coloration.

The team's future goal is to explore simpler methods to replicate this coating and apply it. This endeavor could result in the creation of a more sustainable, biocompatible, and possibly edible UV and blue-reflective paint. The coatings might encompass the numerous functionalities of natural biological ones that offer protection to plants, mirroring them in exactitude.

“Identifying an unknown coloration mechanism on fruits that we frequently grow and consume was indeed fascinating," stated Rox, “It was doubly thrilling to be able to mimic that color by using the harvested wax to develop a fresh blue coating that is uniquely unprecedented."

Rox further expressed, “Transposing all the existing qualities of this natural wax into synthetically engineered materials is what we aspire to!”