As nouns the difference between lecithin and cephalin

is that lecithin is the principal phospholipid in animals; it is particularly abundant in egg yolks, and is extracted commercially from soy. It is a major constituent of cell membranes, and is commonly used as a food additive (as an emulsifier) while cephalin is a phospholipid found particularly in the cells of nervous tissue; it is also the primary phospholipid in bacteria.