Chemical rancidity

Rancidity is associated with characteristic off-flavor and odor of the oil. Rancidity could be as a result of microbial decomposition of fats, oils and other lipids. When these processes occur in food, undesirable odors and flavors can result.

There are two major causes of rancidity. One occurs when oil reacts with oxygen and is called oxidative rancidity.

Fish are the main source of polyunsaturated fatty acids that, unfortunately, are highly susceptible to degradation process, such as oxidation. Oxidative rancidity is a chemical reaction catalyzed by heat, ultraviolet light, heavy metals and oxygen.

Oxidation of fats is caused by a biochemical reaction between fats and oxygen. In this process the long-chain fatty acids are degraded and short-chain compounds are formed. Oxidative rancidity is best controlled by the addition of antioxidants and ‘oxygen scavengers’.

The other cause of rancidity is by a combination of enzymes and moisture. Enzymes such as lipases liberates fatty acids from the triglyceride to form di and/or monoglycerides and free fatty acids and such liberation of free fatty acids is called hydrolysis.

Hydrolysis is also caused by chemical action that is prompted by factors such as heat or presence of water. Rancidity caused by hydrolysis is called hydrolytic rancidity.
Chemical rancidity