Lipid Oxidation

Polyunsaturated fatty acids are well known for its protective effect on human health. However, they contain multiple double bonds which are susceptible to lipid oxidation. These have been long recognized and it is the major challenge in oil industry. Lipid oxidation is the main factor of food deterioration. It not only affects fatty acid composition and the nutritional quality of the food, it also causes undesirable changes in colour, aroma and produce toxic compounds (Wasowicz, 2004). The toxic compounds produce from lipid oxidation, especially lipid-derived aldehydes are very stable. It can diffuse from their site of generation and bring damage at remote locations. Depends on the concentration of the lipid oxidation products, it cause effects

Lipid oxidation is accelerated by prooxidant such as ultra-violet light, high temperature, photosensitizing agents and metal ions (Carocho and Ferreira, 2013). It can happen via three different mechanisms, producing different oxidation products. The three mechanisms are free radical mechanism (autoxidation), photoxidation, and lipoxygenase activity. Among the three mechanisms, autoxidation is the key mechanism that contributes to food deterioration. Autoxidation able occur at low activation energy (4 to 14 kcal•mol-1), moreover, the reaction rate cannot be diminished by storing at the oil at low temperature (Shahidi and Wanasundara,

Lipoxygenase enzymes are activated when tissue is disrupted or injured. The reaction of lipoxygenase activity is similar to auto-oxidation, except that it is selective to the type of substrate. For an example, the polyunsaturated fatty acids, linoleic acid is the substrate for the most studies lipoxygenase, LOX-1. The iron in LOX will must be oxidized by hydroperoxide for the oxidation to proceed. The oxidized LOX abstracts a hydrogen atom from the polyunsaturated fatty caids. As a result, radical is formed and the LOX is reduced to Fe2+ (Makekian et al., 2000)