Rancidity: Why Do Foods Turn Rancid?

Rancidity refers to the complete or incomplete hydrolysis or oxidation of fats and oils when exposed to air, light, moisture, and bacterial activity; this generally occurs in food items, making them undesirable for consumption. In more general terms, rancidity is always associated with food products that contain oil and fatty acids. Fatty acids are nothing but fats, cholesterol, and steroids. Rancidity reactions typically occur in three steps: initiation, propagation, and termination. At the end of rancidification, fats, oils, and other lipids are decomposed, thus forming highly reactive molecules. These are responsible for the unpleasant smell and taste of rancid foods. In some cases, rancidification may also lead to the loss of vitamins in food.