Albumin, al BYOO muhn, also spelled albumen, is a sticky, gelatinlike substance. Its best-known form is the white of an egg. Albumin belongs to the class of foods called proteins (see Protein). The word is spelled albumen when it refers to egg whites, but albumin when referring to the general substance. The albumin of egg white is called ovalbumin. The albumin in milk is called lactalbumin. Serum albumin is the albumin in blood serum. It makes up over half of the protein in blood serum and helps stabilize other serum proteins. Some albumin is found in vegetable matter. All albumins contain carbon, hydrogen, nitrogen, oxygen, and sulfur.