A natural brilliant blue colouring has been discovered by an international team of researchers including chemists at the University of California, Davis. The new cyan blue, obtained from red cabbage, could be an alternative to synthetic blue food colourings says the research team, whose findings have been published in Science Advances.

“Blue colours are really quite rare in nature – a lot of them are really reds and purples,” said Pamela Denish, a graduate student working with Professor Justin Siegel at the UC Davis Department of Chemistry and Innovation Institute for Food and Health.

Having the right blue colour is also important for mixing other colours, such as green. If the blue isn’t right, it will produce muddy, brown colours when mixed, Siegel said.

Red cabbage extracts are widely used as a source of natural food colourings, especially reds and purples. These dyes are called anthocyanins. For about a decade, a team led by scientists at the Mars Advanced Research Institute and Mars Wrigley Science and Technology, in collaboration with the UC Davis Innovation Institute for Food and Health, The Ohio State University, Nagoya University, Japan, the University of Avignon, France and SISSA University, Italy have been working on isolating a blue anthocyanin from red cabbage. But the natural blue colouring is present only in tiny amounts.

Enzymes to convert colours

Denish, graduate students Kathryn Guggenheim and Mary Riley, and Siegel discovered a way to convert other anthocyanins in cabbage into the blue colour compound. They screened public libraries of millions of enzymes for candidates that might do the job and tested a small number in the lab. based on those results, they used computational methods to search a huge number of potential protein sequences – 10 to the power of 20, more than the number of stars in the universe – to design an enzyme that would accomplish the conversion with high efficiency.

“We used these tools to search the universe for the enzyme we’re interested in,” Siegel said.

With this enzyme, they were able to convert the anthocyanin blue from a tiny fraction of red cabbage extract into a primary product, allowing the institute researchers and other collaborators to fully characterise the new blue colouring.