Nutritional and Functional Properties of Egg Proteins

Egg Protein Composition and Quality

Eggs contain proteins that are of the highest quality. It is necessary to distinguish between the white and the yolk, both in terms of quality and quantity.

The Egg White

The egg white, or Clara, consists of clear proteins and almost corresponds to a protein solution. Most of these proteins are biologically active as enzymes, inhibitors, or antibodies. Their functional foaming capacity may diminish or disappear due to heating, freezing, dehydration, mechanical strength, and also by adding some chemicals such as NaCl.

Primary Egg White Proteins

• Ovalbumin: It is the most abundant protein (54%). It has a molecular weight of 45,000. It easily denatures and has many SH groups.
• Conalbumin: Represents 13% of the total. It is the one that has antibacterial activity. It is able to bind iron and other metal ions; this is one of the mechanisms of action against organisms that require this metal for their development.
• Ovomucoid (11%): It is a glycoprotein, being mainly hexosamines. It inhibits the proteolytic activity of trypsin. It is heat resistant, though this resistance decreases as pH increases.
• Lysozyme (3.5%): It is an enzyme. It causes the lysis of some organisms by the cleavage of cell wall polysaccharides.

Fractions of the Yolk

• A. Low-density lipoprotein: Contains 90% of lipids. Represents approximately 2/3 of the dry matter.
• B. Higher density: Contains two types of protein. It sediments in the form of granules.
• C. Soluble proteins.

Yolk Protein Classifications

• Lipoproteins: Lipovitelin (found in fraction B) and lipovitelinin (found in fractions B and C).
• Phosphoprotein: Phosvitin (found in fraction B).
• Soluble fraction: Livetin (found in fraction C).

Functional Properties of the Egg

The properties of the egg include acting as a thickener, agglutinant, coloring, flavoring, and emulsifier, as well as providing protection via protective enzymes.

• Thickener: This is a quality of both the white and yolk. Egg albumin protein coagulation occurs by heat. Examples include boiled eggs used in baking and tortillas.
• Foaming (Sparkling): A quality of the egg white. The major protein, ovalbumin, forms a water-air foam used in pastry and meringue formation.
• Agglutinate: A characteristic of the white and yolk, resulting in the formation of gels to unite various foods, such as pâté.
• Coloring: A property of the yolk that provides characteristic color pigments, used in pasta.
• Flavoring: Brings specific scents to pasta and pastries.
• Emulsifier: Enabled by lecithin, which contains hydrophobic and hydrophilic areas in the yolk, used in mayonnaise.