From blue Dorito crisps to blue candies that colour your tongue, this shade of snacks is popular online – there are even video trends where people only eat blue food for 24 hours. If any of this makes you feel a bit nauseous, it could be because blue food is actually quite rare in nature.
Food manufacturers use chemicals such as “brilliant blue” and “indigotine” as food colourants. However, both dyeing chemicals can have negative side effects on human bodies.
People allergic to brilliant blue dyes can get skin rashes and nasal congestion after consuming them. Studies also show a linkage between indigotine consumption and tumour growth in mice.
Many fruits and vegetables are naturally coloured by four groups of pigments: yellow-orange carotenoids, red-purple anthocyanins, red betalains and green chlorophyll (see graphic).
Then why is the colour blue so rare in nature? Because there is no known chemical compound that makes plants and animals a true blue colour. Most flowers or plants that appear blue are actually a mix of different pigments and colourants.
If you had to name a blue food that exists naturally and without any artificial colouring, 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 unique and vibrant bluish-purple colour.
Nevertheless, blueberries have no blue pigments – if you’ve ever mashed a blueberry, you will know they are dark red.
A study conducted by the University of Bristol shows how blueberries masquerade as blue using an optical illusion.
There is a waxy coat called bloom on the skin of blueberries. The hydrophobic waxy layer is mainly used to prevent the berries from losing water.
When scientists looked closer at the thin and flexible coat, they found tiny and randomly-arranged crystals that scatter blue and UV (ultraviolet) light.
Since human eyes cannot detect UV light, only blue light is reflected into our eyes. Therefore, the light scattering on the waxy coat produces the so-called blue colour, not the blueberry itself. It’s all a trick being played on you by nature.
The same theory applies to other ‘blue-coloured’ food such as damsons, sloes and juniper berries.
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 organisms like plants?
Colour, or pigment, is a powerful communication tool in the macroscopic world. Apart from serving its specific functions, pigments can also give organisms a distinct colour to camouflage, regulate body temperature and send social signals.
Green pigment – Chlorophyll
Chlorophyll is the most crucial and essential pigment for plants. It is necessary for photosynthesis, a process that produces oxygen. Chlorophyll appears green because the green wavelengths of white light are reflected from the plant.
Reddish-purple pigment – Anthocyanins
Anthocyanins provide colour to the stem, leaves, roots, fruits and flowers of plants. It may also change its colour at different pH values.
Yellowish-orange pigment – Carotenoids
Carotenoids are insoluble in water and are attached to the cell membranes. They are also antioxidants that can promote good vision in human eyes.
Red pigment – Betalains
Betalains give plants their colours and are a powerful antioxidant.
