Rancidity: Meaning, Types, Causes, Responsibility & Examples

Rancidity is the process of oxidation of unsaturated fats and oils present in our food items. When exposed to sunlight, air, moisture or a microorganism, unsaturated fats are converted into hydroperoxide, a compound that eventually spoils food.

• Hydroperoxides forms volatile aldehydes, hydrocarbons, esters, alcohol, etc which results in an unpleasant odour and taste in food. 
• Hydrolytic, oxidative, and microbial, enzymatic, and photooxidative rancidity are the five most commonly known types of rancidity. 

Key Terms: Rancidity Meaning, Rancidity, Rancidity of Oils, Steps of Rancidity, Rancid Fats, Oxidative Rancidity, Oxygen Molecules, Unsaturated Fats, Oxidation, Hydroperoxide

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What is Rancidity Meaning?

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The simple meaning of rancidity is the oxidation of unsaturated fats or oils in food that results in a bad smell and taste. When oxygen molecules interact with food and oil, the normal composition of the food is damaged which causes a change in taste and smell, and thus the food is not recommended to be consumed.

• Rancidity leads to Rancidification.
• Rancidification is a condition produced by the aerial oxidation of unsaturated fats present in food and other products that are noticeable by their rotten smell or taste.
• When unsaturated fats are exposed to sunlight, it converts to hydroperoxide and breaks down into volatile aldehydes, esters, alcohols, hydrocarbons, ketones, etc., some of which have an unpleasant odour. 

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Rancidity Process

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Rancidity happens in food products that have oil and fatty acids in them. Fatty acids are mainly formed of fats, steroids, and cholesterol. These are saturated or unsaturated carboxylic acids with a long aliphatic chain. Any substance turns rancid in basically three steps:

1. 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. 

2. 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.   

3. Termination Reaction: In the third stage, two radicals combine together to form a new single bond.

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. 

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Types of Rancidity

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Five types of rancidity are known which are explained in detail below: 

• Hydrolytic Rancidity
• Oxidative Rancidity
• Microbial Rancidity
• Enzymatic Rancidity 
• Photooxidative Rancidity

Hydrolytic Rancidity

Hydrolytic Rancidity refers to the smell or odour that occurs when free fatty acids are released and triglycerides are hydrolyzed.

• Triglyceride is a combination of three fatty acids present in oily food.
• Hydrolytic Rancidity occurs more quickly in the presence of enzymes like lipase and with moisture and heat.
• It results in the hydrolysis of the fats with the liberation of either one or more volatile fatty acids.

Also Read: Chemical reactions Important Questions

Oxidative Rancidity

Oxidative Rancidity causes oxygen damage to a food substance. It occurs with unsaturated fats.

• The natural oil structure is damaged and interrupted by oxygen molecules in such a way that it changes its colour, taste, and smell.
• It leads to the formation of toxic compounds like peroxides that damage Vitamins A and E in foods.
• In Oxidative Rancidity, unsaturated fatty acids of glycerides are oxidized at their double bonds.
• Thus, this reaction causes the release of ketones, volatile aldehydes, and acids.
• It can be prevented by an oxygen-free atmosphere, light-proof packaging, and the addition of antioxidants.

Oxidative Rancidity

Microbial Rancidity

Microbial Rancidity occurs when microorganisms such as moulds or bacteria use their enzymes like lipases to break down chemical structures of fat in oil-producing unwanted smell and taste.

• This process can be reduced by inhibiting microorganisms or by destroying them.
• It can also be reduced by pasteurization and the addition of antioxidant ingredients like vitamin E.

Enzymatic Rancidity

The type of rancidity which is catalysed by the action of enzymes especially lipases and peroxidases is called enzymatic rancidity. 

• These enzymes can be destroyed easily by the heat treatment for a longer time.

Photooxidative Rancidity

The process of rancidity in which free radicals are formed by the action of light is called photooxidative rancidity. 

• Prolonged exposure of light on the food items spoils the taste and odour of the food items.

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Prevention of Rancidity

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There are many possible ways to prevent Rancidity. Some of them are:

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

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Factors affecting Rancidity

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There are various factors that affect rancidity. Some of the factors are discussed below:

• Oxygen: The primary cause of rancidity is exposure to oxygen. Oxygen is more soluble in fats, which leads to food damage and oxidation by releasing free radicals.
• Microorganisms: Many microorganisms release an enzyme known as lipase which leads to the hydrolysis of lipids. These microorganisms use their enzyme on food materials and destroy their chemical composition.
• Physical factors: Physical factors like Heat, light, and temperature plays an important role in rancidification. Heat and light stimulate the process of oxidation and are the main source for the production of free radicals. Light promotes the decomposition of unsaturated fatty acids.
• Trace elements: The rate of rancidity can be increased by trace elements like Fe and Zn. This is another important factor that affects rancidity.

Responsibility

Apart from the natural causes of rancidity, there are some other factors that are responsible for rancidity in foods. Individuals involved in the process of manufacturing, packaging and selling are also responsible for rancid smell and taste in food products. Some of the factors are discussed below:

Manufacturers: They are the first responsible person to ensure the shelf life of the products being manufactured by them.

• Manufacturers may use preservatives or other good quality ingredients to keep food from going rancid. 
• Now, comes the packaging process and it must be done in a proper manner to ensure that the packed items do not come in contact with air.

Regulatory Bodies: All the rules, regulations, & guidelines related to food quality and standards are issued by regulatory bodies.

• Thus, they are one of the responsible authorities to prevent rancidity of food. 
• To check the quality of manufactured food products, these bodies conduct quality testing and inspection. 

Distributors: Individuals involved in storage and distribution are also responsible for protecting manufactured and quality checked food products from spoilage. 

• They have to store food products as per the required conditions. 
• Their primary role when storing food products is to protect the items from air, sunlight, and microorganisms.

Retailers: The responsibility of maintaining the quality of food items at all levels is very important for final sale in the market. 

• Retailers have to ensure the quality and freshness of the food products they are selling to customers. 
• Furthermore, it is their responsibility to remove expired or stale food products from the stock.