Egg yolk is made up of fat, proteins, cholesterols and carbohydrates, weighing approximately 4.5 g, 2.7 g, 210 mg, and 0.61 g respectively. Compared to the white, the yolk accounts for 33 percent of the total liquid content of an egg or egg cell, in the case of non-egg-laying animals. Since it is the source of food for the developing embryo, egg yolk is rich in minerals and vitamins.
In addition to protein, fats, carbohydrates and cholesterol, egg yolk contains fat-soluble vitamins such as vitamins A, D, E and K. One of the reasons egg yolk is of great importance to the development of embryos is that it is among the few food substances that have naturally occurring vitamin D. Egg yolk also contains saturated and unsaturated fatty acids. The unsaturated fatty acids found in egg yolk are oleic acid, linoleic acid, palmitoleic acid and linolenic acid while the saturated fatty acids found in the egg yolk are palmitic acid, stearic acid and myristic acid. The other notable components of egg yolk are lecithin and egg oil. The latter is normally used in cosmetic and pharmaceutical products. Xanthophylls, which are carotenoids, are responsible for the yellow color of egg yolk. The two carotenoids found in large quantities in egg yolk are lutein and zeaxanthin.