Thermostability of hen egg yolk granules: Contribution of native structure of granules

To understand why protein granules resist heat treatment, we measured denaturation, viscosity, and solubility of heated native and disrupted granules and estimated the effect on their emulsifying ability. Granule disruption by sodium chloride caused protein solubility to drop dramatically and viscosity to rise sharply above 72 degrees C. Solubility of native granules was unaffected by heat, and viscosity increased slightly. Electrophoresis revealed that, whatever the granules structure, low-density lipoproteins (LDL) and alpha-high-density lipoproteins (alpha-HDL) were denatured, whereas phosvitin and beta-HDL were resistant to heat. Disrupted granules provided weaker emulsifying ability than native granules. The structure of native granules cannot prevent protein denaturation but can avoid aggregation of LDL and alpha-HDL from different granules.