Egg whites provide several important benefits for developing chicken embryos. The key roles of egg white include:
Nutrition
Egg whites contain proteins, vitamins, and minerals that nourish the growing chick. The major proteins in egg white include ovalbumin, ovotransferrin, ovomucoid, lysozyme, and ovomucin. These proteins provide amino acids that are used to build the tissues and organs of the embryo. Egg white also contains vitamins such as riboflavin, niacin, biotin, and folate, along with minerals like zinc, iron, and copper. All of these nutrients are absorbed by the embryo to support growth and development.
Protection
Egg whites contain several antiviral, antibacterial, and antifungal substances that help protect the embryo from infection. The most notable antimicrobial components of egg white are lysozyme, ovotransferrin, avidin, and ovomucin. Lysozyme breaks down bacterial cell walls, ovotransferrin deprives bacteria of iron, avidin binds biotin to inhibit bacterial growth, and ovomucin forms complexes with certain microbes. These natural defenses are critical for keeping pathogens away from the vulnerable embryo.
Moisture and pH balance
Egg whites provide moisture that keeps the embryo hydrated. They also help maintain a proper pH environment for the embryo through buffering capacitors in the albumen proteins. The pH of thick egg white needs to stay around 7.6 to ensure the embryo develops safely. Too high or low of a pH can harm the chick.
Physical support and shock absorption
The egg white’s gel-like consistency cushions and stabilizes the yolk where the embryo is growing. It provides shock absorption against cracks and movement. Thinner egg white closest to the shell membrane specifically works as a shock absorber. Thicker egg white around the yolk suspends it at the center, keeping the embryo in the optimal position.
Gas exchange
Egg whites allow oxygen to pass through their membrane and be absorbed by the underlying blood vessels surrounding the yolk. This facilitates respiration for the developing embryo. Carbon dioxide waste produced by the embryo can diffuse back out through the egg white.
Water retention
Egg whites control moisture loss from the egg, helping retain a consistent environment for the chick. The inner thin albumen contains higher concentrations of ovomucin, which slows the outward diffusion of water. Without egg whites, excessive water loss could occur and impair embryo growth.
Nutrient transport
As the chick develops, it absorbs egg white proteins and minerals into its blood supply. Substances like antibodies and growth factors are also transferred from the egg white to support the embryo.
Storage of resources
Egg whites hold a reserve supply of nutrients and minerals that can continue providing for the chick after hatching if needed. Any unused egg white is absorbed into the chick’s body in the days after hatching.
Protection from yolk adhesion
Egg whites physically separate the embryo from direct contact with the yolk. This prevents tissues from sticking together and impairing development. It allows freer movement as the chick matures.
Temperature regulation
Egg whites work as an insulator that helps regulate heat within the egg for proper incubation. The thick albumen maintains more stable temperatures around the yolk compared to the outer thin region near the changing environmental air temperature.
Promotion of hatching
Toward the end of incubation, egg white thins and weakens around the chick, making it easier for the chick to break through. Certain enzymes may also soften the membrane between the white and air cell at the broad end of the egg. These physical changes promote the chick’s ability to pip and hatch.
Waste removal
As the chick develops, protein breakdown produces chemical byproducts like ammonia. Some waste can diffuse out through the egg white, removing toxic compounds.
Protection from bacteria
Egg whites contain numerous antimicrobial proteins that protect against bacterial infections. Lysozyme breaks down bacterial cell walls. Ovotransferrin binds and depletes iron needed by bacteria. Avidin inhibits bacterial biotin utilization. Ovomucin forms complexes that inhibit certain bacterial strains. These innate defenses are critical for an embryo developing outside the protection of its mother’s body.
Cushioning against fracture
The thick gel-like egg white cushions the yolk and encased embryo, protecting it from excessive jostling or fractures. The viscosity dampens movement and shocks that could otherwise break the yolk. Egg turning during incubation helps maintain this cushioning effect.
Properties of Egg White Proteins
| Protein | Concentration | Properties |
|---|---|---|
| Ovalbumin | 54% | Supplies amino acids, binds metal ions |
| Ovotransferrin | 12% | Binds iron, antibacterial |
| Ovomucoid | 11% | Trypsin inhibitor, antibacterial |
| Lysozyme | 3.5% | Antibacterial, breaks down cell walls |
| Ovomucin | 1.5% | Gel formation, antibacterial |
This table shows the major proteins found in egg whites and their relative abundance and functional properties. Ovalbumin makes up over half of total egg white protein and provides nutrition through its amino acids. Ovotransferrin, ovomucoid, lysozyme, and ovomucin all contribute to egg white’s antibacterial properties. The unique characteristics of each protein support the developing embryo.
Changes During Incubation
Egg whites undergo important changes during the 21 days of chicken embryo development:
- Thinning – Egg whites thin as water migrates to the embryo and thick albumen is used for nutrition.
- pH increase – pH rises from about 7.6 to 9.7 as CO2 is given off by the embryo.
- Lower antimicrobial activity – Antibacterial proteins like lysozyme decrease later in incubation.
- Gas exchange increases – The inner and outer shell membranes become more permeable to oxygen and carbon dioxide.
- Weakening of membranes – Enzymes soften the membranes attaching the egg white to the air cell and shell.
These changes promote embryo growth and prepare the chick for hatching by making it easier for the chick to pip through the egg. The thinning white and weakened membranes provide less physical resistance for the hatching chick.
Conclusion
Egg whites are a multifunctional part of the chicken egg that nurtures and protects the developing embryo. Key roles include supplying nutrition, defending against infection, regulating optimal environmental conditions like pH and moisture, providing physical support and shock absorption, facilitating respiration, controlling water loss, transporting nutrients, storing reserve nutrition, preventing yolk adhesion, insulating temperature, and promoting the hatching process. The diverse proteins in egg white each contribute unique properties that help the chick grow. Without egg whites, chicks would not have a suitable environment for proper embryonic development.