ABSTRACT

Formation of various free radicals is a common process in biological and food systems. At the cellular level, normal metabolism of oxygen leads to the production of oxygen-derived free radicals which are eliminated efficiently by various cellular defense mechanisms. However, the biological system is also frequently subjected to prooxidant situations wherein the cellular concentration of an activated oxygen species is increased either by overproduction, because of some causative agents, or by a deficiency in the controlling mechanisms. The activated forms of oxygen produced are superoxide, hydroperoxy radical, singlet oxygen, hydroxyl radical, and hydrogen peroxide. Prooxidant states are induced in biological systems by various agents such as hyperbaric oxygen tension, radiation, transition metals, iron and copper, and xenobiotic metabolites. One of the major reactions of these active oxygen species is initiation of lipid oxidation at membranal and cytosolic levels which ultimately leads to cellular degeneration, chromosomal aberrations, mutations, and cytotoxicity. In food systems also, lipids are highly susceptible to oxidation resulting in the formation of cholesterol oxidation products, lipid hydroperoxides, and malonaldehyde. Some of the causative agents are heat, photosensitization, transition metals, metalloproteins, and radiation. Dietary lipid oxidation leads to the development of rancidity, protein damage, and oxidation of pigments resulting in a loss of sensory properties, nutritive value, and shelf life of food products.