Egg whites are one of the most versatile foods because they can foam, gel and also act as emulsifiers. Very little is known about how the proteins inside egg whites bind together to achieve these properties – but X-ray analysis has now given us a better idea.

Nafisa Begam at the University of Tübingen in Germany and her colleagues have used a technique called X-ray photon correlation spectroscopy to understand how proteins form into networks when an egg white is cooked.

“The egg white itself is transparent, but when you cook it, it becomes white and so you can’t use conventional light scattering techniques [to study it],” says team member Fajun Zhang, also at the University of Tübingen. “X-rays can penetrate it much easier.”

The team placed a small sample of egg white on a heated plate in the laboratory and, as it cooked at 80°C, zapped it with an X-ray beam. When the beam hits proteins of different sizes moving at different speeds, it bounces off and scatters at varying wavelengths. Capturing these scatter patterns every 40 milliseconds to produce a total of 20,000 pictures allowed the team to reconstruct the movement of the proteins.

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“The tiny proteins are moving really fast so we need a high-quality detector,” says Begam. X-ray photon correlation spectroscopy has a high resolution, which allowed the team to record small and subtle changes occurring rapidly.

When an egg is heated, the proteins – which have a tangled three-dimensional shape – unfold and form bonds with each other. We knew this happened at a molecular level, but this work shows the network structure developing on a larger, micrometre scale over the first 160 seconds of cooking.

During this time, the team saw an exponential growth in the movement of the proteins. Then movement slowed as the egg white solidified into a gel. This suggests that the egg white forms a mesh-like network of proteins within the first 3 minutes of cooking.

This technique could be used to understand the motion dynamics of other soft systems, says Aurora Nogales at the Institute of Structure of Matter in Madrid, Spain.

Next, the team is interested in investigating how the egg protein network develops when during cooking at different temperatures and with different techniques.

Journal reference: Physical Review Letters, DOI: 10.1103/PhysRevLett.126.098001