Brightest African Fruit’s Color Scheme to Inspire Replacement of Toxic Colors

The brightest fruit of all got its color not because of pigmentation, but because it uses a structural color wherein it reflects light of particular wavelengths, reveals a new study.

Researchers from the University of Cambridge studied the brightest African fruit known as Pollia condensata to find out how they got their shining metallic blue color. 

While most of the bright colors appear due to pigmentation, the research team found that the African fruit looks bright as it uses a structural color. Structural color is commonly seen in the animal kingdom, but it is not known much amongst plant species. The Pollia fruit does not provide any nutritional value, but birds get attracted to them because of their shiny color. Birds might possibly use it as a decorative item in order to attract females for mating.

The fruits that look like beads are tiny and grow on the head of the Pollia condensata plant which is usually 1ft 6in high. They are commonly found in the forests of African nations including Ethiopia, Mozambique, Angola and Tanzania, reported Daily Mail.

When experts examined the fruits, they found that their shiny color changed when the fruits' angle changed. They noticed that the fruits had iridescence similar to peacocks and butterflies. According to the researchers, the fruits' color is possibly a way to disperse seeds. While color obtained by pigmentation loses its shine after some years, the shiny color of Pollia condensata will remain the same forever.

The cellulose strands of the fruits are mounded in multi-layers in the cell wall and form an asymmetrical structure (chiral). Each cell produces color separately. Experts suggested that the shiny color is caused by the reflection of wavelengths from the multi-layers of cellulose. These strands reflect a selective wavelength of light based on the thickness of the layers. 

While thick layers either reflect green or red, the thinner layers reflect blue. As the layers' thickness change, it gives a pixelated or pointillist appearance, researchers wrote in the paper.

"This obscure little plant has hit on a fantastic way of making an irresistible shiny, sparkly, multi-colored, iridescent signal to every bird in the vicinity, without wasting any of its precious photosynthetic reserves on bird food. Evolution is very smart!" Dr Beverley Glover from the University of Cambridge's Department of Plant Sciences, one of the researchers involved in the study, said in a statement.

What is the use of the study?

"By taking inspiration from nature, it is possible to obtain smart multifunctional materials using sustainable routes with abundant and cheap materials like cellulose," said Dr Silvia Vignolini, lead author on the paper from the University of Cambridge's Department of Physics.

"We believe that using cellulose to create colored materials can lead to many industrial applications. As an example, edible cellulose-based nanostructures with structural color can be used as substitutes for toxic dyes and colorants in food. Moreover, the fact that the processes involved in cellulose extraction and manipulation are already used in the paper industry facilitates the use of such materials for industrial applications such as security labeling or cosmetics."

The findings of the study are published in the journal Proceedings of the National Academy of Sciences.