Blueberries might appear to be blue, but it’s all a trick of light! Photo: ShutterstockFrom blue crisps to blue candies that colour your tongue, this shade of snacks is popular online. There are even videos where people only eat blue food for 24 hours. If any of this makes you feel sick, it could be because blue food is rare in nature.
Food manufacturers use chemicals such as “brilliant blue” and “indigotine” to dye blue foods and give them their colours. However, both chemicals can have negative side effects on humans.
People allergic to these dyes can get skin rashes and stuffy noses from them. Studies also show a link between eating indigotine and tumour growth in mice.
Many fruits and vegetables are naturally coloured by four groups of pigments, or chemicals that give them their colour: yellow-orange carotenoids, red-purple anthocyanins, red betalains and green chlorophyll (see graphic).
Why is blue food so rare in nature? Because there are no known chemicals that make plants and animals a true blue colour. Most flowers or plants that appear blue are actually a mix of different pigments.
If you had to name a natural blue food, most people would probably think of blueberries. Blueberries are a popular summer treat because they are juicy and refreshing. Many assume they are blue because of their bluish-purple colour. But blueberries have no blue pigments. If you’ve ever mashed a blueberry, you will know they are dark red.
A study by the University of Bristol shows how blueberries appear blue by tricking our eyes.
The skin of blueberries is covered in a waxy coat called bloom. It is mainly used to prevent them from losing water.
Scientists looked closer at the thin coat and found tiny crystals that scatter blue and UV (ultraviolet) light.
Since human eyes cannot detect UV light, we only see the blue light. Therefore, the light from the waxy coat produces the so-called blue colour, not the blueberry itself. It’s all a trick being played on you by nature.
Then what is the actual colour of blueberries? Dark red. Blueberries contain strong pigments called anthocyanins, which have a deep reddish-purple colour. They can also be found in fruits like mulberries, black currants and black cherries.
What do pigments do in plants and animals?
Colour, or pigment, is a powerful tool in nature. It can help plants and animals hide from predators, regulate body temperature and send social signals.
Green pigment – Chlorophyll
Chlorophyll is the most important pigment for plants. It is necessary for photosynthesis, a process that makes oxygen. Chlorophyll appears green because of the green wavelengths of white light reflected from the plant.
Reddish-purple pigment – Anthocyanins
Anthocyanins provide colour to the stem, leaves, roots, fruits and flowers of plants.
Yellowish-orange pigment – Carotenoids
Carotenoids do not dissolve in water and are attached to the cell membranes. They are also helpful for promoting good vision in human eyes.
Red pigment – Betalains
Betalains give plants their colours and provide healthy nutrients.