What Does the Egg Yolk Contain?

, Health A2Z

What is Egg Yolk?

The egg yolk is also known as vitellus is the nutrient-bearing portion of the egg that supply food for the development and growth of the embryo.

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Egg yolks are often rich in minerals, vitamins, lipids, and proteins.

In some species, the amount of the yolk in an egg cell affects the developmental processes that follow fertilization.

The yolk is not a living cell material like protoplasm, but the largely passive material called deutoplasm.

The food material and associated control structures are supplied during the process of oogenesis.

Chicken Egg Yolk:

In the avian egg, the yolk is of the yellow color, it is spherical and suspended in the egg white by one or two spiral bands of tissue known as chalazae.


The yolk mass, together with the ovum or egg cell properly (after fertilization, the embryo) are enclosed by a vitelline membrane.

Uses of Egg Yolk:

  • The developing embryo inside the egg uses the yolk as energy sustenance.
  • Egg yolk separated from the egg used in cooking.
  • Egg yolk is used for making liqueurs such as eggnog or advocaat.
  • It is also used in extracting egg oil which has various cosmetic, medicinal, and nutritional uses.

Chicken Egg Yolk Composition:

Egg yolk contains about 33% of the liquid weight of the egg, around 2.8 g protein, 0.63 g carbohydrates, 191 mg cholesterol, and 4.66 g total fat.

Fatty acids in egg yolk including;

Unsaturated fatty acids

  • Oleic acid
  • Linoleic acid
  • Palmitoleic acid
  • Linolenic acid


Saturated fatty acids

  • Palmitic acid
  • Stearic acid
  • Myristic acid

      Read more about Egg Nutrition Facts.

Yolk Proteins:

Phosvitins are known as phosphoproteins which are important in sequestering iron, calcium and other cations for the development and growth of the embryo.

Lipovitellins are used for the storage of lipid and metal.


Yolk Minerals and Vitamins:

Yolks hold more than 90% of the iron, phosphorus, calcium, zinc, vitamin B6, thiamine, folate, pantothenic acid, and vitamin B12 of the egg.

It also has fat-soluble vitamins including A, E, D, and K in the egg.


Double-Yolk Eggs:

Double-yolk eggs occur when the ovulation occurs when one yolk becomes joined with another yolk and certain eggs may be the result of a young hen’s reproductive cycle which is not yet being synchronized.

It also mentions that higher-order yolks are rare.


Yolk Color:

The color of an egg yolk is affected by the makeup of the chicken feed.
Its color is generally improved with a feed containing a large component of yellow, fat-soluble pigments like carotenes in dark green plant material.


Health benefits of Egg Yolks:

  • It provides valuable vitamins such as A, D, E and K, antioxidants, and omega-3 fats.
  • The cholesterol found in egg yolks is not affiliated with heart disease or high blood cholesterol levels.
  • The yolk is the healthiest part of the egg.

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