Why are blueberries blue?

Blueberries have an intense dark blue color, researchers have discovered where they come from

Blueberries are dark in color with shades of blue, but when crushed their juice is red, not blue. What happens?

Researchers at the University of Bristol have discovered that the blue color of blueberries is due to tiny external structures in the natural wax layer that covers them. The same applies to many fruits of the same color such as plums, sloes and juniper berries.

In the study published today in Science Advances, researchers show why blueberries are blue despite the dark red pigments in the fruit’s peel. Its blue color comes from a waxy layer that surrounds the fruit and is made up of miniature structures that scatter blue and ultraviolet light. This gives blueberries their blue appearance to humans and their UV blue appearance to birds. Chromatic blue-UV reflection is due to the interaction of the randomly arranged crystalline structures of the epicuticular wax (from the peel of the blueberry) with light.

Rox Middleton, a researcher at the School of Biological Sciences in Bristol, explains: “The blue in blueberries cannot be ‘extracted’ by crushing, as it is not contained in the pigmented juice that can be squeezed from the fruit.” That’s why we knew that there had to be something strange about the color. “So we removed the wax and recrystallized it on cardboard and were able to create a completely new blue UV coating.”

An ultra-thin layer of paint

The ultrafine dye is about two micrometers thick and although less reflective, it is visibly blue and reflects UV rays well, potentially paving the way for new dyeing methods.

“It shows that nature used a really clever trick, an ultra-thin layer for an important dye,” Rox added.

Most plants are covered with a thin layer of wax that has several functions, many of which scientists do not yet understand. “They know it can be very effective as a hydrophobic and self-cleaning coating, but only now are they realizing how important the structure is to the visible coloration.”

Now the team plans to look for easier ways to recreate and apply the coating. This could lead to more sustainable, biocompatible and even edible UV and blue reflective paints.

Furthermore, these coatings could have the same diverse functions as natural biological coatings that protect plants.

Rox added: “It was really interesting to discover that right under our noses there was an unknown color mechanism in popular fruits that we grow and eat all the time.”

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“Even more exciting was being able to reproduce that color by collecting the wax to create a new blue coating that no one had ever seen before.”

Blueberries: Nutrients, Calories and Benefits

Blueberries have numerous health-promoting properties that have been scientifically proven. These properties include:

  1. High antioxidant content: Blueberries are rich in antioxidants, especially anthocyanins, which give them their characteristic blue color. These antioxidants can help fight oxidative stress and reduce the risk of chronic diseases such as heart disease, diabetes and cancer.
  2. Low in calories and high in fiberNote: Blueberries are low in calories, 100 grams have just 57 kcal and they contain 2.5 grams of fiber. In addition, blueberries provide vitamin C, vitamin K and manganese, among other things.
  3. Improved heart health: Eating blueberries has been linked to a reduction in heart disease risk factors such as LDL cholesterol (or “bad” cholesterol), blood pressure, and artery stiffness. Studies suggest that regular consumption of blueberries can improve endothelial function (the inside of blood vessels), which is crucial for cardiovascular health.
  4. Diabetes prevention and control: Blueberries have a low glycemic index, meaning they cause a smaller and slower rise in blood sugar levels compared to other foods. Additionally, studies suggest that blueberries may improve insulin sensitivity, which is important for preventing and treating diabetes.
  5. Support for brain health: Research shows that the antioxidants in blueberries have positive effects on the brain and can improve memory and cognitive function. One study found that regular consumption of blueberries and strawberries was associated with a delay in cognitive decline in older women.
  6. Anti-inflammatory properties: Chronic inflammation is a fundamental factor in many diseases. The bioactive compounds in blueberries have anti-inflammatory properties that may reduce the risk of inflammatory diseases.
  7. Support for urinary health: Eating blueberries has traditionally been associated with preventing urinary tract infections (UTIs). Certain compounds in cranberries are believed to prevent bacteria from attaching to the walls of the urinary tract. However, further studies are needed to confirm this effect.
  8. Benefits for the skin: Thanks to their high antioxidant content, blueberries can help protect skin from sun damage, pollution, and premature aging.

Science continues to research the benefits of blueberries and it is likely that even more beneficial properties of this fruit will be discovered in the future.

REFERENCE

Self-organized, disordered structural color from fruit wax flowers

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