New kind of blue found in cabbage could replace synthetic food dye

A long search for a natural alternative to artificial blue food colouring may have come to an end, with scientists discovering a blue pigment in cabbage that can do the job.

Blue pigments are rarely found in natural resources like plants and rocks, meaning that most blue products – including sweets, drinks, drug tablets, cosmetics and clothing – have to be made using synthetic blue dyes.

These synthetic dyes are typically made from petrochemicals, leading to concerns about their environmental impact and safety as food additives.

Scientists have spent decades searching for natural alternatives. Now, Pamela Denish at the University of California, Davis, and her colleagues have found a pigment in red cabbage similar to the artificial food colouring Brilliant Blue FCF or E133.

This natural blue pigment – a type of anthocyanin molecule – is only present in small amounts in red cabbage.

However, the researchers found they could make larger quantities by treating the dominant red-coloured anthocyanins present in red cabbage with a specially designed enzyme that turned them blue.

The team used the new blue pigment to make blue ice cream, doughnut icing and sugar-coated lentils. These products maintained their blue colour while being stored for 30 days in ambient conditions.

Safety testing must be performed before the natural blue dye can be used in foods, but Kumi Yoshida at Nagoya University in Japan, one of the study authors, says it is unlikely to have adverse health effects. “Red cabbage anthocyanins have a long, long history in our diets,” she says.

The reason why the colour blue is so uncommon in nature is because complex molecular structures are required to absorb the right wavelengths of light to give a blue appearance, says Rebecca Robbins at the Mars Wrigley Global Innovation Center in the US, who was also involved in the study. “It takes quite a [few] specific molecular features,” she says.