Mechanisms of lipid peroxidation and antioxidants

Lipid peroxidation is a general phenomenon which takes place in foods as well as in cellular membranes and lipoproteins. It leads to oxidative dammages with consequences to food preservation and to the development of various diseases. The targets of lipid oxidation are the polyunsaturated fatty acids. Owing to the fact that oxygen can exist under 2 states, a ground state (O-3(2)) and an excited state (O-1(2)), lipid peroxidation can proceed by 2 different reactions. One which involves (O-3(2)), is a free-radical chain reaction with 3 steps (initiation by free radicals, propagation and terminaison), the other which involves (O-1(2)) is a fast reaction with direct addition of oxygen to the double bonds of fatty acids. Both reactions lead to the formation of hydroperoxides as primary products. Hydroperoxides decomposed rapidly to give many secondary products such as lipid free radicals which contribute to increase the oxidation of other molecules such as proteins, nucleic acids and other lipids. Ketones, alkanes (pentane, ethane) and aldehydes (MDA, 4HNE) are also formed by hydroperoxide decomposition. Aldehydes are reactive compounds which bind to the amino group of proteins, nucleic acids and lipids causing dammages to these molecules. The consequences for membranes are alterations of their functions which could lead to cell death. In food hydroperoxide decomposition give rise to qualitative alterations. Lipid peroxidation is a major problem for food industry as well as for human health since it is associated to many diseases. Antioxidants can prevent or delay lipid peroxidation by different mechanisms.