Microstructural changes in stored hen egg yolk

摘要

Microstructural changes in hen egg yolk stored at room temperature (20 deg C +- 1 deg C) for 0, 5, 10, 20, and 30 days were investigated. Yolks frozen with liquid nitrogen were cut into outer, middle, and inner layers, and immersed in the fixation solution. The yolk samples (5mm X 5mm) were dehydrated by ethanol and embedded in epoxy resins. Ultra thin sections were observed with transmission electron microscopy. Other yolk samples were dried with critical point drying methods and observed with scanning electron microscopy. Yolks at day 0 had polyhedral spheres which were closely packed at the vitelline membrane. The ground substrate of yolk spheres was uniform and protein granules were evenly distributed. Vesicles appeared in the ground substrate of eggs stored for ,5 days. After storage, interstitial spaces between yolk spheres in outer layers were broadened and had oval shaped particles released from the yolk spheres. The protein granules within these spheres were unevenly distributed and many of them were fused. Fine spots appeared in the granules. These changes were observed throughout every layer from the eggs stored for 20 days. These results clearly show that the microstructure in the yolk spheres changed with storage.