Red cabbage unlocks brilliant blue: Researchers closing the gap in botanical-based food colors

15 Jul 2021 --- The clean label appetite continues to steer formulators’ hunt for new hues from within nature’s color palette. But botanical sources do not account for every shade of dye – in particular, the search for an authentic blue has yielded limited options. This considerably impedes industry’s ability to bring natural pigments up to par with synthetic food dyes on the basis of performance.

FoodIngredientsFirst speaks to coloring foods specialist GNT and researchers at the University of California, Davis (UC Davis) to explore the most promising advancements in the search for brilliant blue.

The color experts discuss the existing challenges among solutions currently available, which include conventional spirulina – and now, a new blue compound sourced from red cabbage using enzymatic extraction.

“Blue colors are really quite rare in nature – a lot of them are actually reds and purples,” comments Pamela Denish, a graduate student at the UC Davis Department of Chemistry and Innovation Institute for Food and Health in the US.

Denish and her international research team have recently discovered the natural brilliant cyan blue color obtained from red cabbage. This new pigment could be an alternative to synthetic blue food colorings such as the widely used FD&C Blue No. 1.

The UC Davis scientists have founded a start-up company, Peak B, to develop the technology for their new pigment’s application. (Credit: Mars Wrigley) The “right” kind of blue
For about a decade, a team led by scientists at the Mars Advanced Research Institute and Mars Wrigley Science and Technology have been collaborating on this red cabbage project with the UC Davis and other universities in Japan, France and Italy.

So far, the UC Davis researchers have established that our blue compound works in low moisture matrices, such as the sugar matrix used for coating candies.

The scientists have founded a start-up company, Peak B, to develop the technology for the new pigment’s commercial applications.

“We’ve also found that it works in confections such as icing and ice cream,” adds Denish. “We are very interested in testing the compound in baked goods and other dough-based products.” 

Professor Justin Siegel of UC Davis, working with Denish, adds that nailing the right blue color is essential when mixing other colors, such as green. If the blue isn’t right, it will produce muddy, brown colors when mixed.

Limitations of working with anthocyanins
Red cabbage extracts are widely used as a source of natural food colorings, especially reds and purples. These dyes are called anthocyanins.

Comparisons of pigments applied in a candy coating experiment. (Credit: Mars Wrigley)

But anthocyanins are typically only blue at very high pH values, and the color intensity and stability at those values is very low, highlights Jana Reckter, product manager at GNT.

“Most products in the food and beverage industry have a much lower pH, especially confectionery and beverages,” she continues. “As a result, it is very difficult to achieve an effective and stable blue shade based on the anthocyanin pigments from fruit and vegetables.”

“There are very few naturally occurring blue shades available in fruits and vegetables,” she echoes. “A blueberry peel, for example, appears bluish but the juice is red.”

Specifics on spirulina
Spirulina is one of the few natural sources for blue and it has been a part of the human diet for centuries. “There’s evidence that it was consumed for its nutritional properties by Aztecs living around Lake Texcoco in Mexico,” says Reckter.

“Aside from being a foodstuff, spirulina contains a naturally occurring pigment called phycocyanin, which is an excellent natural food coloring and fully water-soluble.”

“Spirulina can deliver excellent results in a broad range of applications and it is also a very on-trend ingredient that is well known by consumers. As such, we consider spirulina to be the best natural solution to deliver vibrant blue shades,” she concludes.

GNT most recently launched a new natural Exberry coloring solution made from spirulina for clean label green hues in F&B applications.

Spirulina’s formulation challenges
But spirulina has a number of industry-recognized limitations, Denish highlights. “First and foremost, the blue color is paler than the vibrant cyan color of synthetic FD&C Blue No. 1.”

“Extracting the blue compound from spirulina algae is also tedious, resulting in a more expensive product that is too pricey for large F&B companies to incorporate into products for people who are not okay with paying a premium for ‘natural’ ingredients,” she explains.

“Additionally, there are textural and blending problems that result in uneven color distribution in a final product.”

Spirulina is one of the few natural sources for blue and it has been a part of the human diet for centuries. (Credit: GNT)The newly discovered natural blue pigment from red cabbage is said to mix well with yellow to produce a vibrant, consistent green. “Spirulina is very challenging to mix in this manner,” Denish points out.

Enzymes to convert colors
Denish, postdoctoral researcher Kathryn Guggenheim, graduate student Mary Riley, and Professor Siegel figured out a way to convert other anthocyanins in cabbage into the blue color compound. Their findings are published in Science Advances.

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, the researchers used computational methods to search a huge number of potential protein sequences – 10 to the power of 20, or “more than the number of stars in the universe” – to design an enzyme that would accomplish the conversion with high efficiency.

With this enzyme, the researchers 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 characterize the new blue coloring.

“We used Rosetta Design to make a mutation to the enzyme sequence that accelerated the reaction to be able to convert about 50 g red cabbage extract to our blue compound in 24 hours,” says Denish.

“This was scaled up from performing experiments at milligram levels, and we are confident that we can scale this to commercially viable levels, as the process is effectively the same as what is used in cheese and beer production.”

Advantages of extracting with enzymes
There are much simpler processes of extracting colors from fruits and vegetables. “For example, you can boil a lot of fruits and vegetables in a pot in your kitchen and get natural dyes,” Denish remarks.

“However, in these cases you’re limited to the hues naturally found in the plants, most of which are oranges, reds and purples,” she continues. “Twenty years of work went into determining which single compound gave the vibrant blue color we wanted.”

Blue-glazed donuts made with the natural spirulina-based Exberry coloring solution by GNT. (Credit: GNT)Most natural color compounds are highly similar, falling into either the anthocyanin or carotenoid class of secondary metabolites. “From there, the diversity of compounds is a result of sugar and acyl groups being attached at different positions on these compounds,” says Denish.

“Enzymes that attach or remove these sugar and acyl groups could contribute to the isolation of any number of unique compounds.”

There are already many examples of enzymes being used in food manufacturing. Enzymes are used in milk and cheese processing (rennet), beer production and meat tenderization (proteases).

They are also found in juice production, in which pectinases and amylases break down insoluble compounds to release soluble sugars that clarify the juice to produce a clearer, sweeter product.

But beyond their traditional applications, enzymes have proven their capacity to help curb off-notes in high protein beverages, maintain label-friendly dough strength, and meet sugar reduction targets in organic lactose-free dairy.

“Enzymes are a part of everything we do, so the possibilities are really endless,” concludes Denish.

For more insights on other novel functional enzymes that deliver on anti-aging, hydration and post-workout recovery, readers may be directed to the FoodIngredientsFirst-hosted report by Innova Market Insights exploring this topic.

By Benjamin Ferrer