US researchers develop new method to produce natural colours for cosmetics

Researchers of US-based Rensselaer Polytechnic Institute (RPI) have developed a new approach to use four strains of Escherichia coli (E. coli) bacteria to convert sugar into an economical natural pigment for cosmetics and food sector applications.

The approach involves a biosynthesis method to produce the natural red anthocyanin pigment commonly found in strawberries. Anthocyanins are plant pigments with the ability to generate a wide range of colours.

RPI's chemical and biological engineering professor Mattheos Koffas said: “For the first time, we are able to completely synthesise anthocyanins in a biological system.

“We feed the bacteria glucose and they do the rest. This demonstrates that an inexpensive technology can produce these valuable compounds.”

To develop a straightforward process for transforming molecular pathways from plant to bacteria, the research team combined genes from bacteria, yeast, and six plant varieties. 

The researchers found that introduction of the complete molecular pathway into a single strain of bacteria is too long for the cell and divided the pathway among four different strains of E.coli to facilitate production of intermediates that easily diffuse out of the bacteria.

Following combination in a single flask, the first bacteria ingested sugar and produced intermediate phenylpropanoic acids that were ingested by the second strain to produce a second intermediate and so forth, leading to anthocyanin production by the fourth bacteria in the chain.

Researchers intend to further optimise each stage of the new process as hundreds of milligrams per litre are required to produce commercially viable anthocyanin.

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Image: The natural red anthocyanin pigment is found in strawberries. Photo: courtesy of Rensselaer Polytechnic Institute.