New natural blue food coloring from red cabbage

A natural brilliant blue food coloring has been discovered by an international team of researchers including chemists at the University of California, Davis. Natural food colorings are in demand, and the new cyan blue, obtained from red cabbage, could be an alternative to synthetic blue food colorings such as the widely used FD&C Blue No. 1. The U.S. National Science Foundation-funded work is published in Science Advances.

The researchers have developed an enzyme to make the blue color in usable quantities. "Blue colors are really quite rare in nature -- a lot of them are really reds and purples," said researcher Pamela Denish.

The discovery has importance beyond food coloring. Having the right blue color is important for mixing other colors, such as green. If the blue isn't right, it will produce muddy, brown colors when mixed, scientist Justin Siegel said.

Red cabbage extracts are widely used as a source of natural food colorings, especially reds and purples. These dyes are called anthocyanins. The collaboration to isolate a blue anthocyanin from red cabbage involved scientists at the Mars Advanced Research Institute and Mars Wrigley Science and Technology; the UC Davis Innovation Institute for Food and Health; Ohio State University; Nagoya University, Japan; the University of Avignon, France; and SISSA University, Italy.

Denish, Siegel and their colleagues figured out a way to convert other anthocyanins in cabbage into the blue color 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 were interested in," Siegel said.

With the enzyme, the scientists were able to convert the anthocyanin blue from a tiny fraction of red cabbage extract into a primary product, allowing the researchers and their collaborators to fully characterize the new blue coloring.

"This project highlights the wide-ranging benefits of investments in computing infrastructure," said Wendy Nilsen, a program director in NSF's Computer and Information Science and Engineering Directorate. "The ability to use computational methods to 'search the universe' has yielded this and many other new discoveries."