Polyunsaturated lipids

It is now widely appreciated that polyunsaturated fatty acids (PUFAs) are highly susceptible to oxidative damage. Indeed, the process of lipid peroxidation was broadly defined as the oxidative deterioration of polyunsaturated lipids by Tappel (1979). The presence of a double... 

Figure 8. 5is-allylic carbon-hydrogen bond. The dissociation energy of this bond is lower than allylic and alky] carbon-hydrogen bonds, and therefore the iiy-allylic bond is favored for attack by LOO which explains the susceptibility of polyunsaturated lipids. 

Harroun, T.A., Katsaras, J., Wassail, S.R. Cholesterol hydroxyl group is found to reside in the center of a polyunsaturated lipid membrane. Biochem. 2006, 45, 1227-33. 

Formation of peroxides by exposure to air and their involvement in polymerization processes is important for surface coating formulations containing polyunsaturated lipids called drying oils. Also nondrying oils, such as soybean oil, are under development as renewable sources for plastics and resins " . ... 

Hydroperoxide formation by the ene reaction path may lead to formation of conjugated double bonds in polyunsaturated fatty acids (see Section V.A) this reaction is concurrent with POV increase. An increase of the CDV, as measured from the absorbance at 233 nm, therefore indicates oxidation of polyunsaturated lipids. A strong correlation exists between CDV predicted from the absorbance in the 1100 to 2200 nm NIR region and CDV determined by the Ti Ia-64 AOCS official method , by UV spectrophotometry at 233 nm. The method was applied to determine CDV for oxidized soybean oil. A secondary absorption maximum of lesser intensity appears in the 260-280 mn range, and is assigned to ketone dienes . 

The use of freeze-drying avoids an inherent disadvantage of spray drying, i.e., the elevated processing temperature, which accelerates the oxidation of polyunsaturated lipids. 

The RDAs for vitamin E are 10 mg and 8 mg a-TEday 1 for men and women, respectively. UK RNI values have not been established for vitamin E since its requirement is largely dependent on the content of polyunsaturated lipids in the diet. However, the Department of Health (1991) suggested that 4 and 3 mg a-TE day 1 are adequate for men and women, respectively. The major food sources of vitamin E are polyunsaturated vegetable oils and products derived therefrom (e.g. maragrine, salad dressings), green and leafy... 

Figure 6.9 Peroxidative destruction of a polyunsaturated lipid initiated by a free radical attack such as by the trichloromethyl radical (CCI3 ).

The aliphatic alicyclic hydrocarbon precursor is not well recognized as the major aliphatic component in dissolved humic substances, although it was previously postulated to occur (II). This precursor might arise from terpenoid hydrocarbon lipids, but the data presented in this chapter favor polyunsaturated lipid precursors that are oxidatively coupled and cyclized by free-radical mechanisms (20). Degradative studies have not identified this aliphatic component in recognizable fragments. The quantitative, structural-model approach presented here combines the results of 13C NMR, NMR,... 

The H-abstraction reactions of peroxyl radicals are related to ET discussed above, as in both cases the same final product is formed, a hydroperoxide. Mechanistically, these two processes are, of course, different. Hydrogen-abstraction reactions by peroxyl radical, including H02-, are common (cf. the autoxidation of polyunsaturated lipids Hasegawa and Patterson 1978 Patterson and Hasegawa 1978 Patterson 1981 Porter et al. 1981 Gebicki and Bielski 1981 Barclay et al. 1989 Zhu and Sevilla 1990 Aikens and Dix 1991 Simic et al. 1992). This H-abstraction reaction may occur inframolecularly as well as infermolecularly [cf. reactions (29) and (30)]. 

Chemical Characteristics of the Oxidative Fluorescence-Producing Reaction and Presumptive Implication of Malonaldehyde The reaction producing measurable fluorescence on polyamide powder can be carried out in the gas phase by exposure to the volatiles from oxidizing polyunsaturated lipids, whether acids, esters, triglycerides, or phosphatides. It can be also carried out within either the oil phase or a water emulsion, and, as noted above, it can be followed in the vapor above an emulsion, providing the pH is 5.5 or below. 

Neither silica nor Whatman filter paper, so exposed, develops fluorescence. As we have indicated, polyunsaturated lipids produce the same fluorescence on polyamide, but not on silica or filter paper. 

For review articles on mechanisms of autoxidation of polyunsaturated lipids see Ref. 158. 

Flaxseed is an oilseed that contains roughly 38 15% oil. ALA, a polyunsaturated lipid, accounts for 52% of the fatty acids in the oil. Flaxseed is also a rich source of plant lignans (up to 13 mg g flaxseed). The interest in ALA and... 

In nature, fish apparently acquire polyunsaturated lipids in one of two ways. The first of them conforms with the concept of Saigent and Henderson (1980), Watanabe (1982) and Henderson et al. (1985), that some species of fish do not need to synthesize long-chain polyenoic acids, since they occur in phytoplankton, which are eaten by zooplankton which in turn are food for fish. Takahashi et al. (1985) described the situation as unsaturated fatty acids being transferred from plant organisms to phytoplankton-eating fish to predatory fish. 

To a certain extent, the composition (including lipid composition) of cows milk reflects feed composition (Bugaud et al., 2001 Ramaswamy et al., 2001). Certain feeding regimes have the potential to increase the level of polyunsaturated lipids in milk and the potential for oxidation (Barrefors et al., 1995 Charmley and Nicholson, 1995 Hermansen, 1995 Focant et al., 1998 Morales et al., 2000 Bugaud et al., 2001 Timmons et al., 2001 Havemose et al., 2004). 

Porter, N.A. 1986. Mechanisms for auto-oxidation of polyunsaturated lipids. Acta Chem. Res. 19, 262-268. 

Fig. 3. Autoxidation of polyunsaturated fatty acids in phospholipid membranes. Addition of oxygen to lipid free radicals is extremely fast. It yields peroxyl radicals ROO which will tend to capture labile hydrogen atoms of neighbouring polyunsaturated lipids. Accidentally produced free radicals will therefore initiate a chain reaction of lipid peroxidation which will propagate along membranes. This process can result in several dozen propagation steps before it is stopped by a termination reaction. Examples of such termination reactions are the recombination of peroxyl radicals and the formation of a stable free radical from a free radical scavenger (scavH). Termination through recombination of low steady-state concentration of alkyl radicals is unlikely in aerobic medium.

Peroxy radicals are either quenched by antioxidants or react with adjacent polyunsaturated lipids by abstraction of hydrogen, thus forming lipid hydroperoxides (ROOH) ... 

Tocopherols and tocotrienols are often discussed as compounds with separate biological, vitamin, and antioxidant functions, although in a comprehensive review of Traber and Atkinson (2007) it was concluded that all of the biological activities of tocopherols and tocotrienols can be understood and derived from their antioxidant activity to protect polyunsaturated lipids from oxidation in membranes. 

The lipid membrane provides shelter for membrane proteins to do their functions. However, instead of working alone, membrane proteins such as ion channels work together with the membrane, such that the lipid composition around the protein actually affects the activation and the functioning of the protein. This idea is largely the essence of the lipid raft model (8), which highlights the importance of lipids in a variety of cellular functions. It has been observed, for example, that rhodopsin, which is the light sensitive membrane protein, favors interactions with polyunsaturated lipids (9). 

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