Angew. Chem. Int. Ed. http://doi.org/f2rvmx (2014)

From the early Renaissance until around the nineteenth century, egg whites were used as a varnish to glossify the surface, saturate the colours and protect pieces of art. They were popular because they are very stable and they do not turn yellow or become brittle like oils and resins. Despite their popularity, however, little is known about why they are stable. Now, researchers at the Rensselaer Polytechnic Institute show that the native structure of egg whites adsorbed on hydrophobic surfaces changes from an α-helix to β-sheet structure, which protects paintings by acting as an oxygen barrier.

Georges Belfort and colleagues soaked hydrophobic polytetrafluoroethylene membranes, which acted as a model for the surface of fresh oil paintings, in ovalbumin (the main protein in chicken egg white) and studied the protein structure using attenuated total reflection Fourier transform infrared spectroscopy. Over 24 hours, the α-helix content of the ovalbumin coating decreased by 73% whereas the β-sheet content increased by about 44%. This suggests that after extended exposure to air, the protein coating contained mostly β-sheets, which are similar to those found in amyloid fibrils associated with neurodegenerative diseases. When the coated membrane was left in a two-compartment chamber with oxygen being fed in the bottom chamber and nitrogen in the top, the rate of oxygen diffusion across the membrane decreased over time and reached zero when four layers of ovalbumin were coated on the surface. It is suggested that the β-sheets trap and prevent oxygen from diffusing to the artwork.