Researchers at the University of Bristol have discovered that tiny external structures in the wax coating of blueberries are responsible for their blue color. This principle applies to many fruits of the same color, including ebony, blackthorn and juniper berries. In the study, published today in Science Advances, researchers show why pigments in blueberry peels appear dark red but blueberries appear blue.
The blue color of blueberries is caused by a layer of wax surrounding the fruit, which is made up of microscopic structures that scatter blue and ultraviolet light. This makes blueberries appear blue to the human eye and blue ultraviolet to the eyes of birds. The blue ultraviolet color reflection of blueberries is produced by the interaction of randomly arranged epidermal wax crystal structures with light.
Rox Middleton, a researcher at Bristol's School of Biological Sciences, explained: "The blue color of blueberries cannot be 'extracted' by squeezing - because it is not in the pigment juice that can be squeezed out of the fruit. That's why we knew there must be something strange about the colour. So we removed the wax and recrystallized it on a card, which allowed us to create a completely new blue UV coating."
The ultra-thin colorant is about two microns thick and, while less reflective, has a distinct blue color and reflects UV rays well, which could pave the way for new colorant methods.
Rox added: "This shows that nature used a very clever trick during evolution - adding ultra-thin layers of an important colorant."
Most plants are coated in a thin layer of wax that serves a variety of functions, many of which scientists still don't understand. They knew wax was very effective as a hydrophobic, self-cleaning coating, but only now did they realize how important the structure of the wax is to visible color.
Now, the team plans to investigate easier ways to recreate and apply this coating. This could result in UV- and blue-light reflective coatings that are more sustainable, biocompatible and even edible. In addition, these coatings can serve the same multiple functions as natural biocoatings that protect plants.
Rocks added: "It's really interesting to have an unknown coloration mechanism discovered right under our noses, on a fruit we regularly grow and eat. What's even more exciting is to recreate this color by harvesting the wax to create a new, never-before-seen blue coating. It's our dream to incorporate all the functionality of this natural wax into an artificially engineered material!"
Compiled source: ScitechDaily