It makes up about 33 percent of the liquid mass of the egg and contains about 60 kcal. It consists of proteins, carbohydrates (mainly glycogen), lipids (mainly phospholipids), mineral salts, and some vitamins. All fat-soluble vitamins (A, D, E, and K) are found in the yolk. It is one of the few foods that naturally contains vitamin D.
The fats of the yolk show particularly high biological value, as they have a good ratio of unsaturated to saturated fatty acids (2:1) and contain a lot of valuable phospholipids (about 30 percent of total lipids, 70 percent of which are phosphatidylcholine or lecithin).
Chicken egg yolk has a yellow color, which is due to the presence of lutein and zeaxanthin (xanthophylls).
