Rancidity caused by the oxidation of unsaturated fats in foods is
a major problem for the food industry. With the trace metals
present in foods acting as catalysts, the unsaturated fats react with
oxygen, producing free radicals and peroxides. These compounds
can destroy many vitamins, reducing the nutritional value of the
food, destroy pigments, bleaching the food, and cause off-odors
and off-flavors. While the portion of fat undergoing such changes
can be small, the resulting off-odors are strong, and very much out
of proportion to the amount of oil or fat involved.