Introduction:
When it comes to storing fat and oil containing foods for a long time, it is important to prevent oxidation and spoilage. One way to achieve this is by using gases to create a modified atmosphere within the storage container. This modified atmosphere helps in preserving the quality and extending the shelf life of the food.

The role of gases:
Different gases can be used for this purpose, but the most commonly used gases are carbon dioxide (CO2), oxygen (O2), nitrogen (N2), and neon (Ne). Each gas has its own unique properties and effects on the stored food.

Carbon dioxide (CO2):
- Effect on food: Carbon dioxide is commonly used in food storage because it inhibits the growth of microorganisms. It helps in preventing the spoilage of food by acting as an antimicrobial agent.
- How it works: CO2 lowers the pH level of the food, making it more acidic, which creates an unfavorable environment for the growth of bacteria and fungi.
- Benefits: By using carbon dioxide, the growth of spoilage microorganisms can be significantly reduced, thus extending the shelf life of the food.

Oxygen (O2):
- Effect on food: Oxygen is known to promote oxidation, which can lead to the deterioration of fats and oils in food. It can cause rancidity and spoilage.
- How it works: Oxygen reacts with the fats and oils present in the food, leading to the formation of free radicals. These free radicals can cause oxidative damage, resulting in off-flavors and loss of nutritional value.
- Limitations: In the storage of fat and oil containing foods, it is important to minimize the presence of oxygen to prevent oxidation and spoilage.

Nitrogen (N2):
- Effect on food: Nitrogen is an inert gas that does not react with the food. It is commonly used as a filler gas or purging gas in food packaging to displace oxygen and create a modified atmosphere.
- How it works: By replacing the oxygen in the storage container with nitrogen, the concentration of oxygen is reduced, which helps in reducing the rate of oxidation and spoilage.
- Benefits: Nitrogen is effective in extending the shelf life of fat and oil containing foods by preventing oxidative rancidity and maintaining the quality of the food.

Neon (Ne):
- Effect on food: Neon is an inert gas like nitrogen and does not react with the food.
- Usage: However, neon is not commonly used in the storage of fat and oil containing foods. It is mainly used in lighting and advertising due to its distinct orange-red glow.

Conclusion:
In conclusion, the gas that is commonly used in the storage of fat and oil containing foods for a long time is nitrogen (N2). Nitrogen helps in reducing the presence of oxygen, which prevents oxidation and spoilage. Carbon dioxide (CO2) is also used to inhibit the growth of microorganisms, while oxygen (O2) is minimized to prevent oxidation. Neon (Ne) is not typically used in food storage and has other applications.