Chapter 1 · Question 12

What is rancidity? Explain why food items containing oil and fat are often packaged in an atmosphere of nitrogen gas. List the methods used to prevent rancidity.

Q12

What is rancidity? Explain why food items containing oil and fat are often packaged in an atmosphere of nitrogen gas. List the methods used to prevent rancidity.

Answer Revealed

Direct Answer:

Rancidity is the spoilage of oils and fats in food due to oxidation by atmospheric oxygen, leading to an unpleasant smell and taste. Nitrogen gas is used in packaging because it is an inert (unreactive) gas that displaces oxygen, preventing the oxidation of fats and oils. Methods to prevent rancidity include: (i) adding antioxidants (substances that prevent oxidation), (ii) storing food in airtight containers to limit exposure to air, (iii) flushing food packages with nitrogen gas, and (iv) refrigeration to slow down the oxidation rate.

Simple Explanation

When you open a bag of stale chips, the bad smell is rancidity — the fats and oils in the chips have reacted with oxygen in the air and gone bad. Chip bags are filled with nitrogen (not regular air) because nitrogen does not react with fats — it just sits there as a protective blanket. Other ways to stop rancidity: add antioxidant chemicals to the food, store in airtight boxes, and keep food in the fridge to slow down the oxidation.

Exam-Ready Structure

Rancidity is a practical everyday example of oxidation that is explicitly covered in the NCERT Class 10 chapter: 1. Definition: When fats and oils present in food items are oxidised, they become rancid and their smell and taste change. This spoilage is called rancidity. 2. Cause: The main cause is oxidation of fats and oils by oxygen present in air. 3. Flushing with nitrogen gas: (a) Food items such as chips contain oils and fats. (b) If oxygen remains inside the packet, the oils and fats can get oxidised and the food may become rancid. (c) Manufacturers flush such packets with nitrogen so that oxygen is displaced. (d) With less oxygen available, oxidation slows down and the food remains fresh for longer. 4. Other prevention methods from the chapter: (a) Adding antioxidants, which are substances that prevent oxidation. (b) Keeping food in airtight containers, which reduces contact with air and slows down oxidation. 5. This is a direct application of the chapter's teaching that oxidation reactions have everyday consequences — unwanted oxidation can spoil food just as corrosion damages metals.

Key Points

Rancidity: spoilage of fats and oils by atmospheric oxidation → unpleasant smell and taste
Cause: fats and oils are oxidised by oxygen in air
Nitrogen flushing: N₂ is inert, displaces O₂ from food packages, preventing oxidation
Antioxidants are added to foods containing fats and oils to prevent oxidation
Airtight containers slow down oxidation by reducing contact with air

Common Mistakes

Thinking nitrogen itself stops oxidation chemically — nitrogen is just a physical barrier that displaces oxygen; it does not react with the food
Confusing rancidity with corrosion — both involve oxidation but rancidity is about food oils/fats, corrosion is about metals

What is rancidity? Explain why food items containing oil and fat are often packaged in an atmosphere of nitrogen gas. List the methods used to prevent rancidity.