Rheological characterization of egg yolk processed by spray‐drying and lipid‐cholesterol extraction with carbon dioxide

The present work studies the rheological properties of avian egg yolks processed by spray‐drying and by lipid‐cholesterol extraction with CO2 under near‐critical conditions. The results have been compared with those obtained from native egg products in order to analyze the effect of processing on the microstructure and rheological properties of egg yolks. The rheological study included linear viscoelasticity measurements by means of dynamic oscillatory shear and creep tests, which provided information about the unperturbed structure of the material, as well as steady‐state flow measurements. The thermal denaturation of proteins, which was produced during the spray‐drying of egg yolk, was responsible for the dramatic change from fluid to gel‐like behavior. The thermal denaturation of proteins promotes the formation of a gel‐like network, which may be attributed to exposure of internal hydrophobic groups that favor protein aggregation. Lipid (and cholesterol) extraction from yolk increased the viscoelasticity functions and flow properties due to the increased protein concentration.