Rancidity – Types, Mechanism, Prevention

Rancidity is a common problem in rendered animal products. It can have detrimental effects on both the quality and safety of the product.

It is caused by the oxidation of fats and oils, leading to the formation of harmful compounds such as free radicals and hydroperoxides.

The best way to prevent rancidity is through proper storage, packaging, and handling techniques, as well as the use of antioxidants to slow down the oxidation process. It is important for manufacturers and consumers to be aware of the potential for rancidity in rendered animal products and take the necessary precautions to ensure the safety and quality of the product. 
Rancidity testing is essential in the feed industry, as a key indicator of product quality and shelf life.

It is conducted to determine the level of oxidation in samples of feed or feed ingredients
Rancidity is a chemical change that results in an unpleasant odour and taste in a fat or oil.

Types of Rancidity
Hydrolytic rancidity
Oxidative rancidityOil becomes rancid due to the decomposition of fats it contains

Milk turns rancid due to not heating it in the humid atmosphere.

Butter changes its smell and taste when it is kept in an open atmosphere for a longer duration.
Hydrolytic rancidity develops due to the presence of moisture and by growth of microorganisms in the fat.

The microorganisms secrete lipases which split the triglycerides into glycerol and fatty acids.

Hydrolytic rancidity of butter releases volatile butyric acid which gives the bad odour and taste.
Oxidative rancidity occurs in oils and fats containing unsaturated fatty acids due to exposure to air.

Unsaturated fatty acids are converted into hydroperoxides, which break down into volatile aldehydes, esters, alcohols, ketones, and hydrocarbons, some of which have disagreeable odours.
Fats contaminated with enzymes like lipase undergo partial hydrolysis and oxidation of unsaturated fatty acids at the double bonds.

This is even brought about by the atmospheric moisture and temperature. Due to this, there is release of hydrogen peroxide giving a bad odour and taste to the fat.

Rancidity can be prevented by antioxidants like vitamin E, vitamin C, phenols, hydroquinone’s, etc.
Rancidity Process: Rancidity happens in food products that have oil and fatty acids in them. Any substance turns rancid in basically three steps:

I. Initiation Reaction: Initiation reaction leads to the formation of radicals on the food substances because of external factors like heat and air that stimulates this reaction. A radical is an atom molecule or ion that has an unpaired electron. These unpaired electrons make radicals very reactive chemical substances. 
RH ⇒ R- + H+
Propagation Reaction: In this step, oxygen present in the atmosphere gives rise to peroxides. These peroxides react further with unsaturated fatty acids and then produce new radicals.   
Termination Reaction: In the third stage, two radicals combine together to form a new single bond.

1. Rancidity – Types, Mechanism and Prevention Jasmine Juliet Teaching Assistant Biochemistry AC&RI, Madurai

2. Introduction Rancidity testing is essential in the feed industry, as a key indicator of product quality and shelf life. It is conducted to determine the level of oxidation in samples of feed or feed ingredients

3. Rancidity Rancidity is a chemical change that results in an unpleasant odour and taste in a fat or oil. Types of Rancidity Hydrolytic rancidity Oxidative rancidity.

4. Examples of Rancidity Oil becomes rancid due to the decomposition of fats it contains M ilk turns rancid due to not heating it in the humid atmosphere . Butter changes its smell and taste when it is kept in an open atmosphere for a longer duration.

5. Types - Hydrolytic rancidity Hydrolytic rancidity develops due to the presence of moisture and by growth of microorganisms in the fat. The microorganisms secrete lipases which split the triglycerides into glycerol and fatty acids. Hydrolytic rancidity of butter releases volatile butyric acid which gives the bad odour and taste.

6. Hydrolytic rancidity

7. Types - Oxidative rancidity Oxidative rancidity occurs in oils and fats containing unsaturated fatty acids due to exposure to air . Unsaturated fatty acids are converted into hydroperoxides , which break down into volatile aldehydes , esters, alcohols, ketones , and hydrocarbons, some of which have disagreeable odours .

8. Oxidative rancidity

9. Types - Oxidative rancidity Fats contaminated with enzymes like lipase undergo partial hydrolysis and oxidation of unsaturated fatty acids at the double bonds. This is even brought about by the atmospheric moisture and temperature. Due to this, there is release of hydrogen peroxide giving a bad odour and taste to the fat. Rancidity can be prevented by antioxidants like vitamin E, vitamin C, phenols, hydroquinone’s, etc.

10. Mechanism Rancidity Process: Rancidity happens in food products that have oil and fatty acids in them. Any substance turns rancid in basically three steps: I. Initiation Reaction:  Initiation reaction leads to the formation of radicals on the food substances because of external factors like heat and air that stimulates this reaction. A radical is an atom molecule or ion that has an unpaired electron . These unpaired electrons make radicals very reactive chemical substances.  RH  ⇒ R -  + H +

11. Mechanism II. Propagation Reaction:  In this step, oxygen present in the atmosphere gives rise to peroxides. These peroxides react further with unsaturated fatty acids and then produce new radicals.    R -   +  O 2  ⇒ ROO -  (peroxide)

12. Mechanism III. Termination Reaction:  In the third stage, two radicals combine together to form a new single bond. ROO -  + ROO -  ⇒ End Products Fats , Lipids and other compounds are decomposed at the end of the rancidification . The process leads to the formation of highly reactive molecules. Thus, food starts smelling unpleasant and tastes bad after rancidity. 

13. Prevention of Rancidity There are many possible ways to prevent Rancidity. Some of them are : Antioxidants ( tocopherols , rosemary extract, ascorbyl palmitate ) can be added to foods that contain oils and fats to slow down oxidative deterioration. To slow down the process of rancidification , food can be stored in airtight containers . Vacuum packing can be done to keep oxygen out .

14. Prevention of Rancidity 4. By adding inert gas such as nitrogen to the bag to replace oxygen. 5. Food items can be kept in the refrigerator . It will reduce the rate of most reactions that take part in rancidity . 6. By storing food in dark places .

15. Conclusion Rancidity is a common problem in rendered animal products. It can have detrimental effects on both the quality and safety of the product. It is caused by the oxidation of fats and oils, leading to the formation of harmful compounds such as free radicals and hydroperoxides . The best way to prevent rancidity is through proper storage, packaging, and handling techniques, as well as the use of  antioxidants  to slow down the oxidation process. It is important for manufacturers and consumers to be aware of the potential for rancidity in rendered animal products and take the necessary precautions to ensure the safety and quality of the product.