Behind the bite: why blueberries and blue cheeses are blue

Scientists have discovered what makes blueberries blue, and blue cheese blue…and the mechanisms are totally different.

If you were to squish open a blueberry you wouldn’t get blue juice. In fact, none of the pigments found in blueberries are blue! Instead, a new study has found that tiny structures in blueberries’ wax coating give them their distinctive colour.

“The blue of blueberries can’t be ‘extracted’ by squishing – because it isn’t located in the pigmented juice that can be squeezed from the fruit. That was why we knew that there must be something strange about the colour,” says Dr Rox Middleton of the University of Bristol’s School of Biological Sciences, who is first author of the paper describing the research in Science Advances.

Most plants are covered in a thin layer of wax, but scientists are only just starting to understand the multitude of functions that wax can play – including in visible colouration.

Closeup photograph of small blue-coloured berries on a bush
Juniper berries (Juniperus scopulorum). Credit: Ed Reschke/Getty Images

In this study, researchers found the layer of wax that surrounds blueberries and some other blue fruits – such as damson plums, sloes, and juniper berries – is made up of randomly arranged crystal structures that scatter blue and ultraviolet light. This scattered light is perceived by humans as blue, and as blue-UV by birds which are able to perceive ultraviolet light.

Photograph of small blue plums on a tree
Damson plums (Prunus domestica subsp. insititia). Credit: Jonathan Billinger CC BY-SA 2.0

“We removed the wax and re-crystallised it on card and in doing so we were able to create a brand new blue-UV coating,” adds Middleton.

The resulting coating is only about 2 micrometres thick – that’s about half the length of a baker’s yeast cell – and visibly reflects blue light as well as UV light, though to a lesser extent than its natural blueberry state.

Photograph of small blue-coloured berries on a shrub
Sloe berries on a blackthorn shrub (Prunus spinosa). Credit:

In different blue food science, researchers have discovered how to create different colours of blue cheese – according to a new study published earlier this week in the journal NPJ Science of Food.

The fungus Penicillium roqueforti is used to produce blue-veined cheese – such as Stilton, Roquefort and Gorgonzola. The researchers found that the distinctive hue is produced through a biochemical pathway that gradually forms the blue pigments, starting at a white colour which progressively becomes yellow-green, red-brown-pink, dark brown, light blue, and finally dark blue-green.

By inducing mutations in the fungus using UV radiation, they were then able to create a variety of strains in which this pathway was blocked at certain points. These could then be used to make cheese with colours ranging from white to yellow-green to red-brown-pink and light and dark blues.

Photo of a petri dish with 6 strains of fungus growing on it, randing from white in colour to yellow, orange, blue and green.
New strains of Penicillium roqueforti. Credit: The University of Nottingham

“The interesting part was that once we went on to make some cheese, we then did some taste trials with volunteers from across the wider University, and we found that when people were trying the lighter coloured strains they thought they tasted more mild. Whereas they thought the darker strain had a more intense flavour,” says Dr Paul Duer, a professor of fungal biology at the University of Nottingham, who led the research.

“Similarly, with the more reddish brown and a light green one, people thought they had a fruity tangy element to them – whereas according to the lab instruments they were very similar in flavour. This shows that people do perceive taste not only from what they taste but also by what they see.”

Uv muts and cheese 850
Left hand side: spectrum of colour strains produced in Pencillium roqueforti (wild type to far right). Right hand side: cross sections of cheeses made with the original (dark blue-green) or new colour (red-brow, bright green, white albino) strains of the fungus. Credit: The University of Nottingham

So what’s next?

Middleton says the dream is to build all the functionality of the natural wax into artificially engineered materials. The team now plan to look for easier ways of recreating their coating to potentially lead to sustainable, biocompatible, and even potentially edible UV and blue-reflective paint.

As for the cheese, the researchers are now looking at working with cheese makers to create new colour variants of blue cheese, with a company called Myconeos established to see if the strains can be commercialised.

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