Using shrimp to keep white bread white

The Pacific Cleaner Shrimp may be the key to keeping white bread white. Due to health concerns surrounding inorganic nanoparticles such as titanium dioxide and zinc oxide, which are traditionally used as whitening agents, there is a search to find organic, bio-compatible analogues as a replacement. Dr Ben Palmer and student Tali Lemcoff at Ben-Gurion University of the Negev have discovered a material in cleaner shrimp that produces a white reflector in nature. By studying the white material found in cleaner shrimp, the researchers discovered a completely new principle in optics. The findings were published in the Nature Photonics journal.

The Pacific Cleaner Shrimp, which may otherwise be known as Jacques from Finding Nemo, uses white stripes on its cuticle and appendages to attract fish, which it then cleans by eating parasites off the fish’s body. The researchers looked into the white stripes and found that they were made of an ultra-thin layer of densely packed particles of a small molecule, isoxanthopterin. While making white materials from thick materials is easy, it is more challenging to use thin materials due to optical crowding, where reflectance decreases at higher packing densities. Despite being less than 5 microns thick, the whiteness produced by the shrimp is extremely bright, making it one of the thinnest and most efficient white materials that exist.

The arrangement of molecules in the particles is the key to the optics. They are arranged in a ‘liquid crystal’, stacked in columns which radiate from the centre of the nanospheres like the spokes of a wheel.

“At first, I thought it was not interesting because the nanospheres were not classic crystals. However, when we looked closer using cryo-SEM and TEM microscopes, we realised not only that the particles are liquid crystals, like those in LCD displays, but that they exhibit birefringence (dual refraction), which is exceedingly rare in the animal world,” Lemcoff said.

This arrangement of molecules is key to overcoming the optical crowding hurdle, allowing particles to be densely packed and reducing the thickness of the layer required to produce bright whiteness.

“It is really one of the first times we have learned an entirely new principle from studying an organism. The shrimp has overcome a seemingly fundamental hurdle in optics by creating particles with this special arrangement of molecules. Now the question is, how can we replicate this effect for creating new materials we could use as food additives in white bread, or in white paint and other applications?” Palmer said.

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