Uncover the microcosm of the eggshell

Uncover the microcosm of the eggshell

Eggs are known to us as chicken eggs and food, and are mainly composed of three parts: eggshell, egg white and egg yolk. Next, let Dabai, who loves to eat eggs, use the scanning electron microscope to explore the mysteries of egg shells with everyone.

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The eggshell is relatively hard and can be used to protect the white and yolk, perform gas exchange and provide minerals for embryonic development. There will be a layer of eggshell membrane tightly attached to the inside of the eggshell. With the help of a scanning electron microscope, we can observe the thickness of the eggshell and eggshell membrane. A cross-sectional scanning electron microscope image of a common egg shell is shown in the figure below.

Figure A: SEM images of eggshell and eggshell membrane

A closer look at the eggshell reveals that it can be subdivided into three parts with varying microstructures:

1. The outer layer of the eggshell is dense and fine, with a certain strength, called cutin (as shown in 2 in the figure below).

2. The middle layer is spongy and densely covered with many small holes (as shown in 3 in the figure below).

3, The inner layer is cone-shaped, and the space between can accommodate air, this layer can be called papillary layer (shown as 4 in the figure below).

Figure B: Eggshell cross-section and three-layer structure (1-eggshell cross-section; 2-shell cutin; 3-middle layer; 4-papillary layer)

Through the energy spectrum element analysis, it is found that the eggshell mainly contains three elements: carbon, oxygen and calcium. It can be inferred that the main component of the eggshell is calcium carbonate. The energy spectrum analysis results are shown in the figure. No wonder there is a saying that egg shells can supplement calcium, but it is not a wise way to eat egg shells, and Dabai does not recommend it~

Figure C: EDS Analysis of Egg Shell Components

Observation on the surface of the eggshell reveals holes with a diameter of about 30 microns, called stomata, which are channels for gas exchange inside and outside the egg. Moisture in the egg can also be volatilized through the stomata, but they also provide channels for microbial invasion. As shown in Figure B1, air pores run through the eggshell. Figure D shows the pores on the surface of the eggshell.

Figure D: Air pores on the surface of an egg

The eggshell membrane is tightly attached to the inner wall of the eggshell. Through scanning electron microscopy, it is found that the eggshell membrane can be divided into two layers (as shown in Figure 2 below): the outer layer of the eggshell membrane and the inner layer of the eggshell membrane.

The outer layer of the eggshell membrane is a protective film formed by the interweaving of fibrous substances. It is loose and porous, and microorganisms can pass through it (as shown in Figure 3 below). The outer layer of the membrane and the papillary layer of the eggshell are tightly attached together, and the fibers on the membrane can interweave and shuttle in the space between the cones on the papillary layer, which increases the bonding connection between them (as shown in Figure 4 below).

The inner layer of the eggshell membrane is relatively dense (as shown in the upper part of Figure 2 below), which can prevent microorganisms from invading the interior of the egg, but is permeable to moisture and gas.

Figure E: The structure of the eggshell membrane under the scanning electron microscope (1-cross-section of the eggshell membrane; 2-two-layer structure of the eggshell membrane; 3-the structure of the outer layer of the eggshell membrane; 4-the outer layer of the eggshell membrane and the papilla layer interwoven in Together)

After observing the microscopic structure of eggshells, Dabai had to marvel at the magic of nature, and even a small eggshell is so wonderful. If you also have a scanning electron microscope, use it to explore the wonderful microscopic world.

Little knowledge about eggs

1. At one end of the oval egg, an air chamber is formed between the eggshell and the eggshell membrane, which can be used to judge the freshness of the egg. The larger the air chamber, the less fresh the egg. As eggs sit longer, water loss increases and the air cells become larger.

2. There is a layer of colloidal protective film on the outside of the eggshell, which can effectively prevent microorganisms from invading the egg. After fresh eggs are washed with water, the protective film will be destroyed, which is not conducive to their storage.