Buzz
The popular nutritional advice to ‘eat the rainbow’ becomes tricky when it comes to blue foods. While we find an abundance of red, yellow, and green foods in nature, blue ingredients are significantly rarer. Even the most well-known ‘blue’ fruit in the grocery store, blueberries, doesn’t quite live up to its name. As a recent study published in the journal Science Advances reveals, blueberries lack blue pigments, making them not truly blue in the purest sense.
In their research, published on February 7, 2024, a team of scientists from Germany and the UK examined how blueberries achieve their distinctive color without using pigments. Most fruits owe their colors to pigments found in their juices (a fact anyone who's ever sliced cherries for a pie knows all too well). However, blueberries don’t follow this pattern, leading the researchers to investigate a more unusual mechanism at work.
The breakthrough came when the scientists turned their attention to the berry’s waxy surface. This layer, which helps keep the fruit clean and protected, also plays a key role in its unique color. By using an electron microscope to study the wax, they uncovered nanostructures that scatter blue and ultraviolet light while absorbing other wavelengths. This phenomenon, known as 'structural color,' is responsible for the blue and indigo shades in plums and juniper berries. A similar effect creates the iridescent greenish-blue of peacock feathers, showing that some natural colors stem from physical structures rather than pigments.
The researchers were also able to recreate these structures in a laboratory setting. By extracting the wax from the blueberry's outer layer, they managed to recrystallize it and isolate the blue-scattering agent, which is only two microns in width. Their findings suggest that this colorant could be used to develop new blue paints and dyes in the future.
'It was fascinating to discover an entirely new color mechanism right beneath our noses, found in common fruits we grow and consume regularly,' said Rox Middleton, study co-author and research fellow at the University of Bristol’s School of Biological Sciences, in a press release.
Blue is an uncommon color in the plant world. Positioned at the high-energy end of the light spectrum, plants cannot afford to reflect it away from their surfaces, as they depend on sunlight for nourishment. Instead, they absorb the blue light while reflecting lower-energy wavelengths, like reds and greens. This accounts for the absence of true blue pigments in nature. Fruits and flowers that appear blue often use a combination of non-blue pigments or, as seen in blueberries, a special colorant in their outer coating.
If you’ve ever wondered why a blue raspberry doesn’t exist in nature, the answer is simple: it’s not a real fruit. Red is so prevalent in nature’s fruits that ice pop manufacturers had to find a way to differentiate between flavors. Their solution was to market the raspberry as blue, taking advantage of the surplus artificial blue dye and the lack of any real blue fruit flavor to pair it with.
