Many synthetic dyes are still used in the food industry, but after the EU demanded warnings against certain synthetic dyes on packaging, the demand for natural dyes has risen. 

"Previous research has shown unwanted side effects in particular in children when consuming certain synthetic dyes," says professor and section leader Henrik Brinch-Pedersen from the Department of Agroecology at Aarhus University.

Together with a group of researchers, he has for a number of years investigated the possibilities of replacing synthetic dyes with natural dyes from carrots. The dye found in purple carrot varieties is called anthocyanin, and is available in shades of orange to red and blue to purple.

Will make orange carrots purple

The orange carrots that we know from the kitchen gardens and dinner tables do not contain anthocyanins, but the purple carrots do. The problem is just that they are far harder to grow.

"These purple carrots are very exotic, and they do not give a particularly large yield. And this is problematic, since you have to use the dye in very large quantities. It is therefore obvious if we could get the common orange carrot to produce anthocyanins. And that is what we have found a way to do,” says Inger B. Holme from the Department of Agroecology. 

The common orange carrot is relatively resistant, so it does not need to be sprayed very much, it gives a great yield and does not bloom prematurely. Therefore, it was precisely the orange carrot that caught the researchers' attention. Here was an opportunity to grow carrots for the extraction of natural and plant-based dyes for food.

Possibility to replace chemistry with plant-based material

It has taken the researchers several years to find at the right way to do it. In an article published in the summer of 2020, the researchers explained that they had found a method that would be able to make ordinary orange carrots purple. 

"When you look at the history of the carrot, you can see that it has not always been orange, like we know it today. It was actually purple to begin with, but through a selection process, the carrots have simply lost the ability to produce anthocyanins, and therefore they have lost the purple color,” explains Henrik Brinch-Pedersen.

By comparing purple and orange carrots, the researchers found that orange carrots still have the genes for anthocyanins - that is, parts of the machinery lying latent in them, but that they simply lack what it takes to kickstart the process of reading them. In other words, they found that orange carrots have the potential to turn purple and produce anthocyanins that can be used as a natural dye.

Two missing genes

But the research did not stop here, because even though the researchers managed to find the mechanism of the orange carrots, it was still a matter of finding what was missing to get the carrots to produce the dye themselves.

“In our initial research, we were able to point out the transcription factors (for, among other things, reading the genes) that cause the carrots to develop anthocyanin color, and we showed that they are missing in the orange varieties. Now, we have actually found the purple carrots' own genes for regulation and transcription, i.e., those that are missing in orange carrots. And it also means that we can recreate them, put them in place in the orange carrot and make it purple,” explains Henrik Brinch-Pedersen. 

It is a step towards being able to create a high production of a stable, natural, and plant-based dye, which can replace the synthetic and chemically produced dyes, which have been much debated. 

Shows the way forward

As a summary of two previous and above-mentioned publications from the researchers, in a third publication they show the way towards a greater production of natural anthocyanin dyes in carrots. 

“Now we have the results, we know how to change the carrots' production of dye. Thus, we have made great strides in identifying genes involved in the biosynthesis of anthocyanin. Therefore, it is now possible for us to modulate the color, stability, and yield of anthocyanin in purple carrots through genetics, and in our latest peer reviewed roadmap article we show different approaches to how to optimise the gene composition to achieve this, just as we shows how we have reached this point. This paves the way for in the future to be able to modify orange carrots to produce anthocyanin with different color shades and in large enough quantities to be used in the food industry,” explains Inger Holme.