Composition and structure of hen egg yolk

Abstract

Unlike mammals, the embryos of birds are not fed by the mother during their development and have no possibility of elimination of metabolic waste. Consequently, the egg yolk provides vital nutrients (proteins, lipids, vitamins, and minerals) that are extremely well metabolized by the chicken embryo. Egg yolk is also a very attractive source of nutrients for humans: Its coefficient of digestive use is comparable to that of milk, and the biologic value of proteins in the egg is even superior to that of milk proteins (Bourgeois-Adragna 1994). Besides, hen egg yolk is a multifunctional ingredient widely used in many food products such as mayonnaise, salad dressings, cakes, pasta, creams, etc. Indeed, it possesses emulsifying, gelling, coloring, aromatic, and antioxidant properties. Each constituent of yolk possesses peculiar physical and chemical characteristics responsible for its own functional properties. Environmental conditions (pH, ionic strength, competition) and preservative treatment (heating, freezing, drying) can influence and modulate these functional properties. Finally, due to its original role as an embryonic chamber, yolk contains many constituents essential for life. Thus yolk represents a major source of active principles usable in medical, pharmaceutical, cosmetic, nutraceutical, and biotechnological industries. © Springer-Verlag Berlin Heidelberg 2007.