The oil and fat present in food items get oxidised in the presence of air forming products having unpleasant smell and taste which turn the food rancid. Rancidity makes the food unfit for eating. This is why antioxidants are added to foods containing oil and fat to prevent oxidation of food. Nitrogen acts as an antioxidant. That’s why oil and fat containing food items are flushed with nitrogen to prevent oxidation. Thus, the food does not turn rancid and remain good to eat for longer time.