The term lecithin came from the Greek word lekithos, meaning “egg yolk”. This name was coined by the discoverer, French scientist Maurice Gobley, in 1850.  He found the nutrient when he separated it from the egg yolk. By the 1930s, most of lecithin sold in the market was from soybean oil. It was a by product of the degumming process of soybean oils. 

There are several differences in the structure of lecithin derived from egg yolk and those derived from plants, such as soy lecithin. To begin with, the structure of lecithin derived from egg yolk is essentially composed of triglycerides and phospholipids, which differs considerably from plant lipid mixtures. 

Egg yolk lecithin contains long chain polyunsaturated fatty acids known as LC-PUFAs, or Arachidonic Acid and Docosahexaenoic Acid. Both are bound phospholipids, the former occurring exclusively in cell membranes, while the latter is found in high amounts in optic nerve membranes. 

Arachidonic acid is involved in signal transduction, and ensures high membrane fluidity. It is important for body weight development. On the other hand, docosahexaenoic acid is required for normal development of the brain, nervous system, and visual acuity. 

Consequently, both these important components of the structure of lecithin in egg yolk play a vital role during pregnancy and infancy. Since babies have only limited capacities, they need arachidonic acid and docosahexaenoic acid to synthesize fatty acids from their precursors. 

On the other hand, the structure of lecithin derived from soy actually consists of three types of phospholipids: phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). Since soy lecithin is obtained in the process of degumming crude soy oil, it contains minimal amounts of hydratable compounds (1.8%), comprised primarily of phosphatides. After going through the synthesizing process, the resulting structure of lecithin is 30-35% crude soy oil and 65-70% phosphatides. Oil can then be removed completely with the addition of acetone. 

In the structure of lecithin derived from soy, the phosphatides consist of glycerides, which are the basic components of soy oil. However, instead of one fatty acid radical, this has been replaced with phosphoric acid. Now, this is different in the case of pure, or chemical lecithin, or phosphatidylcholine, where the phosphoric acid is further changed with choline. But commercially, the structure of lecithin is mostly fatty acids, with roughly the same proportion as that of soy oil, which is 50-57% linoleic acid and 5% linolenic. 

There are different types of lecithin derived from soy: unrefined or natural (including bleach varieties), refined, and chemically modified. All of these have different chemical structures and compositions. For instance, unrefined lecithin contains 17.5% phosphatidylcholine, 15% phosphatidylethanolamine, 10% phosphatidylinositol, 14-18% other phospholipids, 31-34% unrefined soy oil, 13-16% glycolipids, and 2-4% neutral lipids (mostly triglycerides). 

There are actually two meanings to the term “lecithin.” Commercially, the structure of lecithin consists of a mixture of neural and polar lipids that act as emulsifiers and/or lubricants. In biochemistry, it refers to phosphatidylcholine, a phospholipid composed of glycerol, two fatty acids, a phosphate group and choline.