Why fats develop rancid odor?

Fats develop a rancid odor due to the oxidation of their fatty acids. This process is accelerated by heat, light, and exposure to oxygen. The odor of rancid fat is described as being sharp, pungent, and unpleasant. It is caused by the formation of aldehydes, ketones, and other volatile compounds. These compounds are produced when fatty acids react with oxygen to form free radicals. Free radicals are unstable molecules that can damage cell membranes and DNA, leading to spoilage and off-flavors.

The most common type of fat oxidation is autoxidation, which occurs when fatty acids react with oxygen in the air. This process is initiated by the formation of free radicals, which can be generated by heat, light, or metal ions. Autoxidation can be prevented by storing fats in a cool, dark place, and by avoiding contact with metal surfaces.

Another type of fat oxidation is enzymatic oxidation, which occurs when fatty acids are oxidized by enzymes. This process is catalyzed by enzymes called lipases, which are found in bacteria, molds, and yeasts. Enzymatic oxidation can be prevented by controlling the growth of microorganisms in food.