3D structure of protein networks and lipid globules in heat-treated egg yolk revealed by X-ray holo-tomography

Upon heating, egg yolk transforms from a liquid to a grainy gel due to a combination of lipid aggregation, protein denaturation–aggregation–gelation and other processes. This heat-induced solidification of egg yolk can serve as a useful model system for the investigation of protein denaturation and gelation in biological systems in general. Using X-ray holographic tomography, we studied the heat-induced changes in egg yolk on the micron to sub-micron length scale. In contrast to electron microscopy, X-ray holography does not require sample staining, fixation, or drying, which potentially alter the sample and harm sample fidelity. Our results reveal a developing separation between proteins and lipids with fatty components rapidly aggregating into large globules around 40 μ m in diameter. • X-ray holo-tomography offers 3D resolution better than 0.5 μ m for soft biosamples. • Heating egg yolk causes growing separation between proteins and lipids. • Fatty components in cooked egg yolk rapidly aggregate into 40 μ m large globules.