Decomposition of lipids

Haemoglobin-derived haem iron has multiple pro-inflammatory effects resulting from its ability to initiate decomposition of lipid hydroperoxides from PUFAs. In... 

Space does not allow a complete citing of the literature on thermal decomposition of lipids. Nor was it intended to list the hundreds of products which were identified in heated fats and rationalize mechanisms for their formation. The above discussion is an attempt to identify certain factors which influence the fate of lipids in complex biological systems when subjected to high temperature. It should be obvious that the potential for the mulitiple reactions and interactions which could take place in such systems is enormous. 

The first two sections of this book provide the reader with a background on the thermal generation of aromas. Included in these sections are perspectives on the regulatory aspects and the analytical methodologies at the forefront of aroma research. Subsequent sections present original research on aromas derived from various food sources. In addition, we have included a section on mechanistic studies to provide insights into aroma formation through thermal decomposition of lipid, carbohydrate, and amino acid precursors. The final section is entirely... 

Babiy, A.V., and Gebicki, J.M., 1999, Decomposition of lipid hydroperoxides chances the uptake of low density lipoprotein by macrophages, Acta Biochim. Pol. 46 31-42. 

Oxidation of LDL can be divided into different stages i) initiation of lipid peroxidation ii) propagation of PUFA-mediated lipid peroxidation iii) decomposition of lipid hydroperoxides into reactive aldehydes and ketones, and iv) modification of apo B, leading to recognition of LDL by the macrophage scavenger receptor. 

Figure 5.2 Non-enzymatic degradation of 9- and 13-HPODE and 5- and 15-HPETE. (a) Transition metals and vitamin C mediate the decomposition of lipid hydroperoxides and produce several reactive, bifunctional electrophiles 4-hydroperoxy-2-nonenal,...

Because phospholipids enhance the decomposition of lipid hydroperoxides, they stimulate the formation of flavor-active volatiles in meat and meat products (Mot-tram, 1999). 

Raspberry ketones prevent obesity or counteract a constitutional tendency toward obesity by promoting the decomposition of lipids accumulated in the adipose tissues. But these ketones are poorly soluble in water and have a characteristic aroma even at an extremely low concentration, so it was impossible to add an amount capable of exerting a lipolytic or anti-obese effect to cosmetics, drinks, or pet foods [29]. Flowever, by including raspberry ketones into CyDs the solubility is increased and the specific odor is reduced, resulting in a marked improvement of the taste and stabUity. Importantly, the lipolytic and anti-obese effects are not affected by the complexation. 

Decomposition of Lipid Hydroperoxides ( Off-Flavor Oxidation Products)...387... 

A large body of scientific evidence suggests that the progressive loss of food palatability during lipid oxidation is due to the production of short chain compounds from the decomposition of lipid hydroperoxides. The volatile compounds produced from the oxidation of edible oils are influenced by the composition of the hydroperoxides and positions of oxidative cleavage of double bonds in the fatty acids. ... 

Lee SH, Oe T, Blair lA. Vitamin C-induced decomposition of lipid hydroperoxides to endogenous genotoxins. Science 2001 292 2083—2086. 

Trace amounts of heavy metals, such as iron and copper, have a marked accelerating effect on the rates of lipid oxidation. The homolytic decomposition of lipid hydroperoxides is generally considered to be metal-catalysed, because it is very difficult or nearly impossible to eliminate traces of metals that can act as potent catalysts. Metals may produce radicals by two pathways ... 

In actual lipid oxidation, one cannot overlook the critical role of trace metals, which complicate the kinetic sequences of initiation and decomposition of lipid hydroperoxides. These metals catalyse both initiation of free radicals and decomposition of hydroperoxides, which become particularly significant with polyunsaturated lipids containing more than two double bonds. With these polyunsaturated lipids, although the yields of hydroperoxides are reduced in the presence of metals, they produce volatile decomposition products that have a serious impact on flavor deterioration. In foods and biological systems, the mixture of trace metals and hydroperoxides is the most important initiator that plays a key part in the development of free radical oxidation and rancidity. The use of artificial azo compounds as initiators to study free radical oxidation is therefore not relevant. 

Flavor deterioration of food lipids is caused mainly by the presence of volatile lipid oxidation products that have an impact on flavor at extremely low concentrations, often at the parts per billion (ppb) levels. An understanding of the sources of volatile oxidation products provides the basis for improved methods to control and evaluate flavor deterioration. The decomposition of lipid hydroperoxides produces carbonyl compounds, alcohols and hydrocarbons under various conditions of elevated temperatures and in the presence of metal catalysts. 

Transition metal-promoted hydroperoxide deconposition is inqiortant to the oxidative stability and quality of foods for several reasons. First, the abstraction of hydrogen from an unsaturated fatty acid results in the formation of a single alkyl radical. Followii hydrogen abstraction, oxygen adds to the alkyl radical to form a peroxyl radical and subsequent abstraction of a hydrogen from another fatty acid or antioxidant to form a lipid hydroperoxide (Figure 1). These reactions by themselves do not result in an increase in free radical numbers. If these reactions were tiie only steps in tiie lipid oxidation reactions, the rapid exponential increase in oxidation that is commonly observed in lipids would not occur. Transition metal-promoted decomposition of lipid hydroperoxides results in the formation of additional radicals (e.g. alkoxyl and peroxyl) which exponentially increase oxidation rates as they start to attack otiier unsaturated fatty acids. 

Figure 3.50 Oxidation fission of alk-2-enals formed by decomposition of lipid hydroperoxides.

ROO") produced by lipid oxidation, or with alkoxyl radicals (RO ) arising by decomposition of lipid hydroperoxides. They provide these radicals with hydrogen, thereby interrupting the radical chain autoxidation reaction. The resulting products are phenoxyl (aryloxyl) radicals of antioxidants ... 

Fat is, on the one hand, a source of taste and aroma compounds and, on the other, a medium that regulates the distribution of these compounds between water, fat and vapour phases, which influence their perception by the sense organs. Some flavour compounds result from the decomposition of lipids by lipolysis, oxidation (section 3.3.4), and microbial or thermal degradation. These processes may produce free fatty acids, aldehydes, ketones, lactones and other volatile compounds (Figure 5.10). 

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