We’ve noticed that if we store any food item at room temperature for an extended period of time, it goes stale. It is caused by the oxidation of food when it comes into contact with air, which causes it to smell and taste bad. It can be avoided by following a few precautions, such as keeping food in the refrigerator. Microorganisms’ activity will be slowed, and their shelf life will be extended.
Rancidity
Rancidity is the oxidation of oils or fats in the food that causes a foul odour and flavour. When unsaturated components of a fatty substance are exposed to sunlight, they can break down into esters, volatile aldehydes, ketones, alcohols, and hydrocarbons, some of which have foul odours.
Rancidity is an unpleasant odour or flavour caused by the airborne oxidation of unsaturated fat found in meals and other products. When unsaturated components of a fatty material are exposed to air, they are transformed into hydroperoxides, which then break down into volatile aldehydes, esters, alcohols, ketones, and hydrocarbons, some of which have unpleasant odours.
The above-mentioned process, as well as hydrolysis, which releases volatile and malodorous acids, mainly butyric acid, causes butter to get rancid. At normal temperatures, saturated fats like beef tallow are resistant to oxidation and rarely go rancid.
For example,
- A stale packet of chips has a distinct odour.
- When butter is kept open for a long duration, the flavour and smell change.
Factors that affect Rancidity
There are various factors that affect rancidity. Some of the factors are discussed below:
- Oxygen: Exposure to oxygen is the major cause of rancidity. Because oxygen is more soluble in lipids, it causes food oxidation and damage by producing free radicals.
- Microorganisms: Many microorganisms produce lipase, an enzyme that causes lipid breakdown. These microbes employ their enzyme to break down the chemical content of food.
- Factors of nature: Rancidification is influenced by physical elements such as heat, light, and temperature. Heat and light drive the oxidation process and are the primary sources of free radical generation. The breakdown of unsaturated fatty acids is aided by light.
- Trace elements: Trace elements, such as Fe and Zn, can speed up the pace of rancidity. Another key aspect that impacts rancidity is temperature.
Prevention of Rancidity of Food
The term “rancidity” refers to the process of food containing fat and oil coming into contact with ambient oxygen and undergoing auto-oxidation, which results in a foul odour and a change in taste. Almost any meal has the potential to go rotten. The word is especially applicable to oils. Oils are especially vulnerable to rancidity due to their chemistry, which makes them vulnerable to oxygen attack.
Metabolic interaction between fats and oxygen causes the oxidation of fats. Long-chain fatty acids are destroyed and short-chain molecules are generated during this process. Butyric acid is one of the reaction products, and it is this acid that gives the rotten taste. The degradation of fats, oils, and other lipids by hydrolysis, oxidation, or both are known as rancidification. In glycerides, hydrolysis separates fatty acid chains from the glycerol backbone. Following are the ways to prevent rancidity:-
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Addition of Antioxidants – Antioxidants are the most effective way to keep food from becoming rancid. Antioxidants are added to fat-containing foods to prevent rancidity from forming due to oxidation. Types of antioxidants:
- Natural antioxidants.
- Synthetic antioxidants.
- Semisynthetic antioxidants – Gallic acid, propyl gallate.
- Metal chelators – citric acid, phosphoric acid.
- Oxygen scavengers – ascorbic acid.
Flavonoids, polyphenols, ascorbic acid (vitamin C), and tocopherols are all-natural antioxidants (vitamin E). Butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), propyl-3, 4, 5-trihydroxybenzoate (also known as propyl gallate), and ethoxyquin are examples of synthetic antioxidants. Natural antioxidants have a short shelf life, whereas synthetic antioxidants have a longer shelf life and perform better. Water-soluble antioxidants are ineffective in stopping direct oxidation within fats, but they are useful in intercepting free radicals that pass via food’s watery portions.
- Addition of Sequestering Agents – Metals are bound by sequestering agents, which prevent them from initiating auto-oxidation. EDTA (ethylene diamine tetra acetic acid) and citric acid are examples of sequestering agents.
- Proper Storage of Fats and Oil Food – Another strategy to prevent food from becoming rancid is to store it properly, away from the effects of oxygen. Because heat and light accelerate the rate of reactivity of lipids with oxygen, rancidification can be reduced by storing fats and oils in a cold, dark environment with little exposure to oxygen or free radicals. Do not add new oil to vessels that already have old oil in them. The old oil will cause a reaction, causing the new oil to get rancid faster than if it were stored in a clean, empty vessel. Allow tanks to drain and dry thoroughly before use, as this will speed up the problems related to oxidation.
- Packing in Nitrogen Gas – Nitrogen is fed into the liquid to remove the oxygen dissolved in the juice, generating bubbles that carry the oxygen, which is then removed from the juice. Nitrogen is utilized in the winemaking business to prevent oxidation, allowing for the use of fewer chemicals. In the food packaging sector, nitrogen gas has long been utilized to help protect the freshness, integrity, and quality of the delivered product. Nitrogen gas is also commonly utilized for food packaging because it creates a pressured environment that inhibits container collapse.
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Keeping food in a Refrigerator Storing in Airtight Containers – Food is kept in airtight containers because of the following reasons:
- It keeps food fresh and also prevents rancidity.
- It prevents the growth of bacteria and entry of foreign substances that can contaminate the food.
- Have the ability to retain the original flavour and aroma of the food.
- Keeps the food hygienic.
Mostly food having high water content is stored in Refrigerator. Bacterial growth is slowed by refrigeration. Bacteria can be found almost everywhere in nature. They can be found in the earth, air, and water, as well as the meals we eat. When bacteria have access to nutrition (food), moisture, and warm temperatures, they multiply quickly, reaching a stage where some germs might cause illness. Bacteria grow most quickly at temperatures between 40 and 140 degrees Fahrenheit, with some strains doubling in size in as little as 20 minutes. Most items can be kept safe in a refrigerator set at 40 degrees Fahrenheit or lower.
- Away From Light – is stored away from light, since light can cause meals to spoil more quickly. Photodegradation can be accelerated by both natural and artificial light. Food oxidation is prevented and rancidity is delayed when it is kept away from light.
Sample Questions
Question 1: What is the reactant and product in the given chemical equation :
2Mg(s) + O2(g) △→ 2MgO(s)
Answer:
In the given equation, Mg and O2 are the reactants and MgO is the product.
Question 2: Differentiate between Oxidation and Reduction.
Answer:
In Oxidation oxygen is added or hydrogen is removed, whereas in Reduction hydrogen is added or oxygen is removed.
Question 3: What is a Redox Reaction?
Answer:
Redox reaction is a reaction in which oxidation and reduction both occur simultaneously.
For Example – Cuo +H2→Cu +H2O
Question 4: Name different ways to prevent Rancidity of food.
Answer:
- Adding AntiOxidants
- Packaging in Nitrogen Gas
- Keeping in a Refrigerator Storing in Airtight Containers
- Away From Light
Question 5: Why food is kept in refrigerators?
Answer:
Because bacteria thrive in humidified environments with high temperatures. However, a refrigerator is a chilly location with no humidity or warmth, which inhibits the growth of microorganisms. This is why food may be kept in the refrigerator for longer periods of time.
Question 6: Which type of foods are stored in refrigerators?
Answer:
Foods with a high water content are prone to spoilage. As a result, it should be kept in refrigerators. Cucumber, watermelon, tomatoes, and other fruits and vegetables should also be kept in the refrigerator.
Question 7: Why some types of food are stored away from the light?
Answer:
Food is stored away from light, since light can cause meals to spoil more quickly. Photodegradation can be accelerated by both natural and artificial light. Food oxidation is prevented and rancidity is delayed when it is kept away from light.