Effect of pH and added electrolyte on the thermal-induced transitions of egg yolk

Thermally-induced transitions of egg yolk were studied using Differential Scanning Calorimetry (DSC) and temperature-controlled Small Amplitude Oscillatory Shear (SAOS). The influence of composition (pH and electrolyte content and type) was analysed. The results obtained under DSC measurements suggest a continuous evolution in protein denaturation that depends on pH and salt content. Cure experiments performed using SAOS show dramatic increases in viscoelasticity functions. Protein gelation is affected by the pH, ionic strength and salt type. SAOS was also used to obtain the mechanical spectra of egg yolk dispersions and gels as a function of composition. The microstructures of gels were also evaluated by Scanning Electron Microscopy (SEM). SEM results reveal an increase in microstructure homogeneity and a decrease in the size of aggregates at lowered pH. The influence of pH and ionic strength on linear viscoelastic properties and microstructure may be explained in terms of the model for the formation of gel networks of globular proteins. However, the characteristic structure of native yolk must also be considered.