Electrophoretic and Chromatographic Changes in Egg Yolk Proteins Due to Heat

Polyacrylamide gel electrophoresis and diethylaminoethyl-cellulose ion-exchange chromatography were used to observe changes in egg yolk products which were heat treated at 3°C intervals from 54 to 84°C for 3.5 min. The USDA pasteurization temperatures of 61.0, 63.3°C for plain, 10% sugared, and 10% salted egg yolk, respectively, had little effect on their electrophoretograms. Only the γ-livetins in plain yolk were slightly affected. Higher temperatures progressively altered these proteins until they disappeared from the electrophoretograms from plain yolk ca 73°, sugared yolk ca 76°, and salted yolk ca 79°C. The lipovitellin fraction and phosvitins were similarly affected by increasing temperatures. Sugar and salt at 10% levels had a protective effect against heat, allowing respectively ca 3° and 6°C higher temperatures before heat damage occurred. The chromatograms from plain and sugared yolk were little affected by pasteurization. However, major changes were noted between unheated and pasteurized (63.3°C) salted yolk. Patterns for salted yolk, pasteurized at 63.3 and 68.0°C were similar, which further indicated that this product can be pasteurized at 68.0°C without significant damage.