Scientists come up with non-toxic blue dye - thanks to the beetroot

A cheap and safe b lue is the most elusive hue in the edible world. Any other component of the rainbow is readily available in vegetables and fruits.

But producing a low-cost blue colouring safe for consumption has stumped experts for decades.

Now an international team has come up with BeetBlue - after tweaking the structure of a natural antioxidant found in beetroot juice.

Non-toxic and cheap, it will enliven clothes, furnishings, hair dyes and many other commodities and surfaces as well as food, they say.

What is more, the plant pigment that gives beetroot its rich, purple-crimson colour is betanin - that has been shown to suppress the development of cancer.

Corresponding author Professor Erick Bastos said: "As far as safe, natural dyes with no metal content go, the colour blue has proven particularly tricky to pin down.

"BeetBlue dissolves easily in water and other solvents and maintains its colour in acidic solutions."

His researchers used a chemical cocktail that increased the wavelength of light reflected by betanin which pushed it towards the blue end of the spectrum. The colour we see is a result of which wavelengths are reflected back to our eyes.

It offers an alternative to expensive blue colourants that often contain poisonous metals - limiting their scope, Prof Bastos said.

What is more, beetroot has been hailed a 'superfood'. There has been evidence it lowers blood pressure, boosts exercise performance and even prevents dementia.

Prof Bastos, an organic chemist at the University of Sao Paulo, Brazil, explained: "Beetroots are rich in betanin, a member of the betalain class

of antioxidants.

"They are commonly used as additives to brighten foods with their yellow-orange or red-violet colours."

But naturally blue betalains do not exist. So Prof Bastos and colleagues developed the new compound - and named it 'quasibetalain.'

Since the dye, described in Science Advances, is intended for human contact, they carried out a series of safety experiments.

These showed it was non-toxic for live zebrafish embryos - as well as human

cells grown in the lab.

Prof Bastos said: "The notion natural means healthy and safe to consume has increased the demand for natural colour ingredients for food, cosmetics and drugs.

"However, finding high performance and economically viable natural colourants is difficult, especially for blue hues.

"Blue mineral pigments inspired artists to represent the blue sky and waters, but despite their usual high stability, these materials are often expensive and contain toxic metal molecules that limit their broad application."

Brightly coloured animals depend on the reflection or emission of light

their surfaces, he explained.

Examples include the blue wings of the jaybird, the Common Blue butterfly, the feathers of the male Indian peacock and the hairs of the blue carpenter bee.

Prof Bastos said: "Since the natural blue colour of most living organisms cannot be easily harnessed, there is a quest for new blue chemicals that could be converted into coloured commodities."

Blue natural pigments are rare, especially among plants, although there are highly evolved flowers that have blue-coloured petals to attract bees and wasps, which are red colour blind.

These include the blue hydrangea, the cornflower, morning glory and speedwell, said Prof Bastos.

To showcase BeetBlue's potential the prototype was incorporated into cellulose, cotton fabric, yoghurt, hair and silk.

Added Prof Bastos: "Under magnification, a uniform blue colour distribution was observed, reaffirming the applicability of BeetBlue as ametal-free blue colourant."

Beetroot was brought to Britain by the Romans. It is rich in fibre, combating constipation and lowering cholesterol levels too.

The vegetable has been shown to increase the number of white blood cells, which are responsible for detecting and eliminating abnormal cells.