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Blueberries: Blue, even without color pigments
Photo: Kativ / Getty Images
With blueberries, the color is even in the name. Not with plums or grapes, they are still blue. What they have in common is that none of the fruits have blue color pigments. Researchers at the University of Bristol have therefore taken a closer look at them. They come to the conclusion: Tiny structures in the wax coating give them their color. The group published the results in the journal “Science Advances”. The magazine “Scinexx” first reported this.
For the study, the group led by first author Rox Middleton examined fruits with a wax coating, which lies like a fine, dusty layer around the fruits. According to them, the pigments in the peel are dark red, even if the fruit is not. This becomes apparent when you press the fruit into juice: grape juice, for example, is dark red. "That's why we knew there had to be something strange about the color," Middleton said, according to a statement.
The researchers removed the wax layer from various blue fruits in order to examine them. They found “that a structural color mechanism is responsible for their appearance,” says the study. The scientists measured this using a method that examines the reflection of light.
The result: The wax layer that surrounds the fruit consists of tiny structures that scatter blue and ultraviolet light. This causes the fruits to look blue to humans. The researchers write that it is probably because these structures are arranged randomly that the fruits have different shades of blue.
The wax layer has various functions that have not yet been fully developed, it goes on to say. But this also includes a self-cleaning or water-repellent function. However, the fact that the layer would also play such a large role in the coloring is new. "It was really interesting to find out that there is an unknown coloration mechanism right under our noses in popular fruits that we grow and eat all the time," Middleton said.
The group now wants to continue research and look for ways to recreate the coating and make it usable. For example, to create a more sustainable and even edible UV and blue reflective paint.
ani