Glossary of Fats and Oils

There is a lot of misunderstanding when the conversation turns to supplemental fat in your livestock or poultry diet. This glossary will acquaint you with some of the terms we regularly use when talking about fats and oils.

Active Oxygen Method (AOM)

AOM is a measure of the ability of a fat to resist oxidative rancidity during storage. An oil or fat is subjected to conditions known to accelerate degradation to help gauge the sample’s resistance to oxidation. Oxygen is bubbled into a fat to cause oxidation of the fatty acids. The peroxide value test is used to monitor oxidation after the sample is stressed under controlled conditions for a long time or until a specific peroxide value is achieved.


Antioxidants are molecules that slow or prevent the oxidation of other chemicals. Oxidation is a redox chemical reaction that transfers electrons from a substance to an oxidizing agent. Oxidation reactions can involve the production of free radicals, which can form dangerous chain reactions. Antioxidants can terminate these chain reactions by removing radical intermediates and can inhibit other oxidation reactions by being oxidized

Extra Caloric Effect

A term used to describe the increased calories available for utilization by animals when fats and oils are added to the diet. The addition of fats and oils to feed diets increases the amount of time it takes for the diet to make its way through the animals digestive tracking, allowing more time for all of the diet to be absorbed for utilization by the animal.

Fatty Acid Profile (FAP)

The FAP is used to determine the quantities of each individual fatty acid, which make up the overall composition of the oil. It can be used as an identification aid and also to determine the composition of vegetable oil or animal fat mixtures.

Free Fatty Acids (FFA)

A nonesterified fatty acid released by the hydrolysis of a triglyceride. An FFA test measures the acidity and then expresses it on a fatty acid basis. The presence of high concentrations of free fatty acids in feed-grade fat, particularly whole animal fats, may mean the fat is rancid. However, some fat sources such as acidulated soapstocks can contain high amounts of free fatty acids without being rancid.

Garrett Formula

A metabolizable energy formula developed by Dr. Roger Garrett through extensive research at Cornell University. Dr. Garrett proved that the factors of moisture, insolubles, unsaponifiables, long-chain fatty acids, phospholipids, oxidized fatty acids, and oligomers reduce the metabolizable energy of fatty acids while total fatty acids and unsaturated fatty acids increase the metabolizable energy.

Insoluble Matter (I)

Contaminants found in used oils due to dust, dirt, wear particles or oxidation products are called insoluble matter. It is often measured as pentane, toluene or benzene insolubles to characterize the nature of the insoluble material.

Iodine Value (IV)

Iodine value is a measure of unsaturation in fats and oils. While not a specific measure of fat stability, iodine number measures can indicate the potential of a fat to be oxidized. The method ensures the reaction of iodine with double bonds of unsaturated fatty acids. Fats with a great number of double bonds provide more sites for oxidation.

Metabolizable Energy

The net energy available to an animal after the utilization of some energy in the processes of digestion and absorption and the loss of some of the material as being undigested or indigestible.


MIU is an abbreviation for the tests moisture, insoluble impurities, and unsaponifiable matter. This value provides information about non-fat and oil components of food and feed grade fats and oils and is used primarily to screen incoming materials for feed or industrial applications.

Moisture (M)

The amount of moisture in a material is determined under prescribed conditions and expressed as a percentage of the weight of the moist specimen, that is, the original weight comprising the dry substance plus any moisture present. Moisture can be determined using moisture balance or Karl Fischer Titrator.

Peroxide Value (PV)

Peroxide value is the measure of the present state of rancidity of a sample. It is also called initial peroxide value (IPV) because it is determined on a sample as submitted. Fresh non-rancid fats have a low PV — usually less than 5. The PV of unstabilized fat can change quickly. For this test, peroxides are indirectly measured under standardized conditions. The result is called the peroxide value, expressed as milliequivalents of peroxide per kilogram of fat.


pH is a measure of the activity of hydrogen ions (H+) in a solution and, therefore, its acidity or alkalinity. The pH value is a number without units, usually between 0 and 14, which indicates whether a solution is acidic (pH 7).

Saponification Value

The saponification value is the weight in milligrams of potassium hydroxide needed to completely saponify one gram of fat. It can give additional indication of the average molecular weight of the fatty acids in a fat, but this test provides less useful information than the fatty acid composition determined by gas chromatography.

Total Fatty Acids (TFA) Content

TFA is considered the sum of fatty acids expressed as triglycerides, which takes into account all sources of fatty acids in a food. This would include the fatty acids from mono-, di-, and triglycerides, other fatty acids, phospholipids and sterol esters.

Unsaponifiable (U)

Unsaponifiable matter includes those substances frequently found dissolved in fatty acids that cannot be saponified by caustic treatment but are soluble in normal fat solvents. Included are the higher aliphatic alcohols, sterols, pigments, tocopherols, and hydrocarbons.