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Oxidation is an irreversible process by which molecular oxygen combines with nutrients in food, a process which will decrease the quality of the food by creating rancidity. Oxidation occurs in different rates depending on factors such as moisture, light, oxygen availability, temperature and presence of metals.

Different types of oils have different susceptibility rates of oxidation. Marine oil, which has a high number of polyunsaturated fatty acid (PUFA), is more susceptible to oxidation than vegetable oil. A variety of chemical compounds such as peroxides, aldehydes and free fatty acids are created as oil oxidizes. Therefore, measuring oxidation involves testing all the breakdown of the chemical components. The tests listed below are the most commonly used to monitor oxidative degradation.

Peroxide Value (PV) measures the amount of primary oxidation products in fresh oil. Generally, the lower the PV, the better the quality of the oil. The result is expressed as milliequivalents of peroxide per kilogram of fat.

Anisidine Value (AV) measures aldehydes, which are secondary products of oxidation and are more stable than peroxides. Aldehydes are responsible if a rancidity smell is present in oil. The lower the AV, the better the quality of the oil. The AV test should be used together with the PV test.

Totox Value is calculated by the formula AV + 2PV to indicate the overall rancidity state of the oil.

Free Fatty Acid (FFA) Value measures the amount of free (unbound) fatty acids, which are cleaved from the parent molecules such as triglycerides or phospholipids. When fats and oils become rancid, individual fatty acids are liberated and make the material slightly acidic. The FFA test measures this acidity and then expresses it on a fatty acid basis.

TBA Rancidity monitors the secondary oxidative aldehyde products. These aldehydes react with 2-Thiobarbituric Acid (TBA) forming a condensation product that is easily measured. However, the test is unsuitable for complex food because the reagent would interact with samples containing carbohydrates or proteins.

Iodine Value measures the unsaturated linkages in oil and fat. It is expressed in terms of percentage of iodine that is absorbed. The decline in iodine value can be used to monitor lipid oxidation.

SGS scientists and technicians can expertly conduct the tests listed above as well as other relevant tests to determining the quality and physical properties of fats and oils. For more information, please contact:

Foong Ming Koh
Agricultural Services
SGS North America, Inc.
900 Georgia Avenue, Ste 1200
Deer Park, TX 77536
t: 281-478-8271
f:  281-478-4793
Website: www.sgs.com/us-agriculture

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