Lipid peroxidation free radical chain reactions

Deterioration of food lipids by free radical chain reaction and lipid peroxidation is a major problem for food manufacturers. The main route of deterioration of vegetable oils is rancidity deriving from the oxidation taking place at the insaturation sites of the fatty acids in the triglyceride molecules. In general the higher the number of double bonds, the easier is... 

Halliwell, B. and Gutteridge, J.M.C. (eds). (1989). Lipid peroxidation a radical chain reaction. In Free Radicals in Biology and Medicine. 2nd edn. Clarendon Press, Oxford, pp. 188-276. 

Hydroxyl radicals are the most reactive free-radical species known and have the ability to react with a wide number of cellular constituents including amino-acid residues, and purine and pyrimidine bases of DNA, as well as attacking membrane lipids to initiate a free-radical chain reaction known as lipid peroxidation. 

The foods can be protected against lipid oxidation either by the addition of antioxidants or by packaging in vacuum or inert gases to exclude oxygen. The antioxidants can be of various types. They can work as "chain-breakers" that interfere with the free radical chain reaction, as "metal inactivators", that bind otherwise pro-oxidative metals, or as "peroxide destroyers", which react with hydroperoxides to give stable products by nonradical processes (1). 

On the other hand, unsaturated lipids may act as secondary mediators of the MnP/Mn system, in a mechanism known as lipid peroxidation, which is a free radical chain-reaction proceeding via the oxidation of unsaturated lipids [32, 33]. Thiols may also undergo oxidation by MnP/Mn and produce thiyl radicals, which in turn mediate in the oxidation of a variety of compounds [34]. 

Free radical chain reactions, which occur during lipid peroxidation, lead to formation of lipid hydroperoxides that decompose to several types of secondary free radicals and a large number of secondary reactive compounds, such as aldehydes, all resulting in the destruction of cellular membranes and other cytotoxic responses. 

Historically, vitamin E has been recognized as necessary for neurological and reproductive functions, for protecting the red cell from hemolysis, and for prevention of retinopathy in premature infants. Inhibition of free-radical chain reactions of lipid peroxidation is the most thoroughly defined role of vitamin This occurs mainly within the polyun-... 

Reactive free radicals extract electrons (usually as hydrogen atoms) from other compounds to complete their own orbitals, thereby initiating free radical chain reactions. The hydroxyl radical is probably the most potent of the ROS. It initiates chain reactions that form lipid peroxides and organic radicals and adds direcdy to compounds. The superoxide anion is also highly reactive, but has limited hpid solubility and cannot diffuse far. However, it can generate the more reactive hydroxyl and hydroperoxy radicals by reacting nonenzymatically with hydrogen peroxide in the Haber-Weiss reaction (Fig 24.4). 

Sulfur-containing amino acids like cysteine, methionine and tripeptide glutathione are very powerful antioxidants that participate in different stages of free-radical chain reactions of biomolecule oxidation [18]. For example, cysteine participates in the synthesis of taurine, the substance that effectively blocks the peroxide oxidation of lipids by binding hypochlorite anion to form chloramine complex. In any organism, cysteine and glutathione reduces the oxidized form of vitamin C to its initial active form while methionine (being an... 

Lipid oxidation in foods is a complex chain of reactions that first consist of the introduction of a functional group containing two concatenated oxygen atoms (peroxides) into unsaturated fatty acids, in a free-radical chain reaction, that afterward gives rise to secondary oxidation products. Different pathways for lipid oxidation have been described radical mechanism or autoxidation, singlet oxygen-mediated mechanism or photooxidation, and enzymatic oxidation. 

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