Chromatography Identifies an Elusive Natural Blue Food Colouring

It must be said, blue foods are in something of a minority. Blueberries and blue smarties are about as far it goes. Blue is one of the most challenging colourants to get, and it is even harder to get from a natural edible source.  Of course, it is possible to make artificial colours, but chefs and consumers are demanding natural products more and more.

But help could finally be at hand. An article - Discovery of a natural cyan blue: A unique food-sourced anthocyanin could replace synthetic brilliant blue - published in the journal Scientific Advances reports on how an international team of scientists have obtained a new cyan blue from red cabbage. And chromatography was at the core of the work.

You don’t want muddy colours

Having the right blue colour is important to help produce other colours in the colour palette such as green. If the blue isn’t just right, then the subsequent colours can be muddy, brown colours when mixed. The main artificial blue colours are a brilliant blue and indigotine, these produce cyan and indigo, respectively. Naturally occurring blues are limited and have a violet colour contribution which can produce muddy green colours when mixed.

Green colours are abundant in nature, but the chlorophyll chromophore is unstable and not water-soluble meaning it has limited applications in the food industry. If scientists can find a cyan blue from natural sources, it would allow a much wider palette of naturally obtained colours to be used in the food industry. “Blue colours are really quite rare in nature – a lot of them are really reds and purples,” said Pamela Denish, a graduate student at the University of California at Davis who worked on the project.

Red cabbage – a multitude of colourants

Red cabbage is used as the starting point for many natural food colourings, particularly reds and purples. The compounds responsible for these dyes are known as anthocyanins. For over a decade a team of international researchers have been working to separate a blue anthocyanin from red cabbage. One of the problems is that the blue colouring is present in tiny amounts.

So, the team have found a method that uses enzymes to convert other anthocyanins in red cabbage into a natural blue colour compound. Enzymatic conversions are nothing new in the food industry, they are the driving force behind cheese manufacture for example. The team used chromatography to both purify the enzymes and colourant and to analyse the natural blue colour to determine it make-up. The power of chromatography is discussed in the article, Faster Time to Results for Ultra-Performance Liquid Chromatographic Separations of Metal-Sensitive Analytes.