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Oyster-friendly microalgae may colour food blue-green

By Stephen Daniells , 21-Jul-2008
Last updated on 30-Jul-2008 at 11:45 GMT

The blue-green pigment from microalgae responsible for the greening of oyster gills may also provide a natural blue-green colouring for food, says new research.

The compound called marennine, produced by the microalgae Haslea ostrearia, not only has potential to act as a pigment, but it also “exhibit[s] significantly higher antioxidative and free radical scavenging activities than natural and synthetic antioxidants commonly used in food,” said a new study in the Journal of Agricultural and Food Chemistry.

The pigment shows excellent properties for use in foods, including high water solubility, high resistance to heat and light, and stability at the pH range 6 to 8, according to researchers from five French universities and institutes.

“Of course, further metabolic and toxicological investigations are needed to demonstrate that marennine could be used as a food grade supplement, but no toxicity related to the pigment has ever been reported during all the time marennine-greened oysters have been eaten by humans,” wrote lead author Jean-Bernard Pouvreau from the University of Nantes.

The market for natural colourings is growing, buoyed by consumers’ concerns regarding artificial food colourings and flavourings.

The issue of artificial colourings came to a head with the FSA-funded study conducted at Southampton University and published in The Lancet last September. It concluded that cocktails of food colourings commonly used in confectionery and beverages, and sodium benzoate, can aggravate hyperactivity in children.

For many consumers, particularly in Europe, blue colourings in food are mostly associated with Nestle Rowntrees’ Smarties brand. The company stopped producing blue Smarties when it promised to remove all artificial colourings from the confectionery amid concerns that they are linked to hyperactivity and may pose other health risks.

The blue Smartie was replaced by a white one, while a suitable natural alternative was found to the colouring Brilliant Blue (E133). After an extended period of development, the blue Smartie is now back thanks to Spirulina, which is produced from two species of cyanobacteria (blue-green lake algae).

New study

Pouvreau and co-workers evaluated marennine from Haslea ostrearia using two kind of antioxidant tests –antioxidant capacity assays, such as beta-carotene and thymidine protection assays, and iron reducing power assay, and assays scavenging DPPH, superoxide, and hydroxide free radicals.

The results showed that the pigment had a higher activity that other natural and synthetic antioxidants commonly used in food, said the researchers. These included ascorbic acid, butylated hydroxyanisole (BHA), and Trolox.

“The apparent antioxidant properties of marennine might be beneficial to the antioxidant system of the human body and also raise the possibility of it being used as a protective agent against the oxidative damage of food products,” wrote the researchers.

“Because of its blue-colouring property and water solubility, it could also be used as a natural food-colouring additive,” they added.

A rosy future for the blue-green pigment

The researchers noted that cultivation of the microalga would need to be optimised if marennine was to be produced industrially. Moreover, purification of the pigment would also need optimised.

Previous research by the same scientists, however, has already proposed how this could be done. The technique includes semipreparative technical procedures, like ultrafiltration through membranes, which could easily be scaled up to a larger production system,” they said.

Source: Journal of Agricultural and Food Chemistry Published online ahead of print, ASAP Article, doi: 10.1021/jf073187n“Antioxidant and Free Radical Scavenging Properties of Marennine, a Blue-Green Polyphenolic Pigment from the Diatom Haslea ostrearia (Gaillon/Bory) Simonsen Responsible for the Natural Greening of Cultured Oysters”Authors : J.-B. Pouvreau, M. Morancais, F. Taran, P. Rosa, L. Dufosse, F. Guerard, S. Pin, J. Fleurence, P. Pondave

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