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Solubility, electrophoresis, viscosity and emulsifying properties of heated solutions of yolk, plasma and granules were determined. Plasma and yolk were not affected when heated under 69ЊC. Above 69ЊC, protein solubility dropped sharply and apparent viscosity rose sharply because of aggregation of proteins. For granules, protein solubility and apparent viscosity were not modified up to 76ЊC. The constituents of granules were not denatured. Emulsifying activity of yolk and plasma decreased after heating at 72ЊC but remained steady for granules. Emulsion stabilization properties of yolk, plasma and granules were not influenced up to 76ЊC. Results suggested that intact granules withstood more severe heat treatments than egg yolk without lessening their emulsifying properties.

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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°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 ␣-high-density lipoproteins (␣-HDL) were denatured, whereas phosvitin and ␤-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 ␣-HDL from different granules.