Oxidation is the chemical reaction in which oxygen interacts with food components, particularly fats, pigments, and certain vitamins, leading to changes in the food, which are usually undesirable.
Lipid, or fat, oxidation leads to rancidity, off-flavors, and loss of nutritional value, especially in oils, nuts, and processed meats.
Oxidation can also cause discoloration in fruits and vegetables, such as browning in cut apples and potatoes, due to enzymatic activity. To mitigate these effects, antioxidants – either naturally occurring (e.g., vitamin E, ascorbic acid) or synthetic (e.g., BHA, BHT) — are added to foods, and packaging technologies aim to limit oxygen exposure through vacuum sealing or inert gas flushing.