Study reveals why blueberries are blue

Researchers at the University of Bristol have solved the mystery behind the blue color of blueberries. The study reveals fascinating insights into the natural world and potentially paves the way for innovative color technologies. 

The study was led by Rox Middleton, a research fellow at Bristol’s School of Biological Sciences. 

Wax coating 

The team has discovered that the blue hue of blueberries, along with several other fruits such as damsons, sloes, and juniper berries, is not due to the pigmentation within the fruit itself but rather the result of tiny structures within the wax coating that covers the fruit.

The research delves into the specifics of how blueberries exhibit their characteristic blue despite the dark red color of the pigments in the fruit skin. The experts found that the blue appearance is created by a layer of wax enveloping the fruit. 

Blue-UV coloration 

The wax layer contains miniature structures that scatter blue and ultraviolet (UV) light, producing the blue-UV coloration visible to both humans and birds. 

This chromatic blue-UV reflectance stems from the interaction between the randomly arranged crystal structures of the epicuticular wax and light, a mechanism previously unknown.

Finding the blue of blueberries 

“The blue of blueberries can’t be ‘extracted’ by squishing – because it isn’t located in the pigmented juice that can be squeezed from the fruit. That was why we knew that there must be something strange about the color,” explained Middleton.

“So we removed the wax and re-crystallized it on card and in doing so we were able to create a brand new blue-UV coating.”

This ultra-thin colorant, which is about two microns thick, is visibly blue and reflects UV light – hinting at the possibility of new colorant methods inspired by nature’s design.

“It shows that nature has evolved to use a really neat trick, an ultrathin layer for an important colorant,” said Middleton.

Broader implications 

The research adds to our understanding of the functional complexity of the wax coatings found on most plants. These coatings are known to serve various purposes, including acting as a hydrophobic, self-cleaning layer, but the study highlights their critical role in visible coloration as well.

Looking forward, the research team aims to explore simpler methods of recreating and applying this coating, which could lead to the development of sustainable, biocompatible, and even edible UV and blue-reflective paints. Such coatings could emulate the multifunctional capabilities of natural biological coatings that protect plants, offering promising applications in various fields.

Exciting results

“It was really interesting to find that there was an unknown coloration mechanism right under our noses, on popular fruits that we grow and eat all the time,” said Middleton.

“It was even more exciting to be able to reproduce that color by harvesting the wax to make a new blue coating that no-one’s seen before. Building all that functionality of this natural wax into artificially engineered materials is the dream!”

More about blueberries 

Blueberries are small, round fruits that are known for their sweet and slightly tart flavor, making them a popular choice for use in a variety of culinary dishes like pies, muffins, and jams. 

Health benefits

Blueberries are also celebrated for their health benefits; they are rich in vitamins C and K, dietary fiber, and particularly high in antioxidants, which are compounds that protect your body from free radicals, molecules that can damage cells and contribute to aging and diseases like cancer.

Cultivation

These berries are native to North America but are now grown in many parts of the world, including Europe, South America, and Asia. 

The cultivation of blueberries involves two main types: highbush blueberries, which are the most commonly cultivated variety and stand about 4-7 feet tall, and lowbush or “wild” blueberries, which are smaller, more intensely flavored, and grow closer to the ground.

Harvesting

The harvesting season for blueberries varies by geographical location, but generally, in the Northern Hemisphere, it runs from April to September. Blueberries can be enjoyed fresh, frozen, or dried and have become a staple ingredient in health-conscious diets due to their nutrient-rich profile. 

In addition to their dietary benefits, blueberries play a role in cultural traditions and festivals in some regions, celebrating the harvest and heritage of blueberry cultivation. Whether enjoyed as a snack or used as a key ingredient in recipes, blueberries continue to be a beloved fruit around the world.

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