It may seem strange that there are no more blue fruits, as many fruit-eating animals, especially those that rely on vision, are particularly sensitive to the color blue. However, some fruits appear blue, although they do not have a blue pigment.
Scientists at the University of Bristol studied dark-colored fruits such as blueberries, plums, and juniper berries and found that their appearance is determined by structural color mechanisms.
In a new study, researchers have revealed why blueberries have a dark red color, but they still look blue. It turns out that the blue color comes from a layer of wax around the fruit, which contains tiny structures that scatter blue and ultraviolet light.
This gives blueberries a blue color to the human eye and a blue ultraviolet light to the bird's eye. Blue UV reflection occurs because of the interaction between the crystal structure of the wax and the light.
Middleton, a researcher at the Bristol School of Biological Sciences, explained that the blue color of blueberries cannot be extracted by pressing because it is not in the pigment juice.
The researchers removed the wax and recrystallized it to understand this, resulting in a completely new blue UV coating.
This ultra-thin colorant, which is about two microns thick, is distinctly blue and reflects UV rays well, which may open up new possibilities for colorant methods.
Nature often uses a thin layer of wax on plants, and it has a variety of functions, including hydrophobicity and self-cleaning. However, until now, scientists have not realized the importance of the structure of this wax for visible color.
The researchers plan to explore more readily available ways to rebuild and apply this coating, which could result in more sustainable, biocompatible, and even edible UV and blue reflective coatings. These coatings also offer a variety of functions, similar to natural bio-coatings that protect plants.
Middleton highlighted the excitement of discovering an unknown coloring mechanism in common fruits such as blueberries and being able to propagate this mechanism to produce a new blue coating. The goal is to integrate all the functions of this natural wax into an artificially engineered material.
Why are blueberries blue?