When food containing oil and fat is kept in an open air, it undergo oxidation and become rancid; due to which their smell and taste changes. This process is called rancidity.
Usually, to avoid rancidity in food containing oil and fat, substances are added which prevent oxidation. Such substances are known as antioxidant substances. Food kept in air-tight containers helps to slow down its oxidation and rancidity is retarded.
Manufacturers of potato chips flush bags of chips with gas such as inactive nitrogen gas as antioxidant to prevent the oxidation of potato chips.