Chemical composition

Triglycerides are the predominant component of most food fats and oils.

The minor components include mono- and diglycerides, free fatty acids, phosphatides, sterols, fatty alcohols, fat-soluble vitamins, and other substances.

A triglyceride is composed of glycerol and three fatty acids. When all of the fatty acids in a triglyceride are identical, it is termed a "simple" triglyceride. The more common forms, however, are the "mixed" triglycerides in which two or three kinds of fatty acids are present in the molecule.

Mono- and diglycerides are mono- and diesters of fatty acids and glycerol.
They are used frequently in foods as emulsifiers. They are prepared commercially by the reaction of glycerol and triglycerides or by the esterification of glycerol and fatty acids.

Free fatty acids are the unattached fatty acids present in a fat. Some unrefined oils may contain as much as several percent free fatty acids. The levels of free fatty acids are reduced in the refining process. Refined fats and oils ready for use as foods usually have a near to nil free fatty acid content.

Phosphatides consist of alcohols (usually glycerol), combined with fatty acids, phosphoric acid, and a nitrogen-containing compound.
For all practical purposes, refining removes the phosphatides from the fat or oil.

Although sterols are found in both animal fats and vegetable oils, there is a substantial difference biologically between those occurring in animal fats and those present in vegetable oils. Cholesterol is the primary animal fat sterol and is only found in vegetable oils in trace amounts. Vegetable oil sterols collectively are termed "phytosterols." Sitosterol and stigmasterol are the best-known vegetable oil sterols. The type and amount of vegetable oils sterols vary with the source of the oil.

Long chain alcohols are of little importance in most edible fats.
A small amount esterified with fatty acids is present in waxes found in some vegetable oils.
Larger quantities are found in some marine oils.

Fats and oils are very good sources of vitamin E.
The fat-soluble vitamins A and D sometimes are added to foods which contain fat because they serve as good carriers and are widely consumed.

Tocopherols are important minor constituents of most vegetable fats. They serve as antioxidants to delayrancidity and as sources of the essential nutrient vitamin E. There are four types of tocopherols varying in antioxidation and vitamin E activity. Among tocopherols, alpha-tocopherol has the highest vitamin E activity.

Carotenoids are colour materials occurring naturally in fats and oils.
Most range in colour from yellow to deep red. The levels of most of these colour bodies are reduced during the normal processing of oils to give them acceptable colour, flavour, and stability.