Linoleic hydroperoxide products

Interaction of lipid hydroperoxides with DNA gives fluorescent products, which cause structural changes in the DNA. Of the fluorescent products formed in the reaction of methyl linoleate hydroperoxide with adenine, FeS04, and ascorbic acid the 4,5- and 2,5-dihydrooxadiazoles (198) and (199) have been identified <88BBA(962)37l>. 

Figure C4.2.4 (A) SP-HPLC of methyl hydroxyoctadecadienoates obtained from linoleic acid hydroperoxide products. Peak 1, methyl 13-hydroxy-9(Z),11( )-octadecadienoate peak 2, methyl 13-hydroxy-9( ),11(E)-octadecadienoate peak 3, methyl 9-hydroxy-10(E),12(Z)-octadecadi-enoate peak 4, methyl 9-hydroxy-10( ),12( )-octadecadienoate. In this chromatogram, peaks 2 and 4 are more abundant than ordinarily encountered retention times may vary (but not the order of elution) depending on the type of silica HPLC column. (B) CP-HPLC of peak 1 from A. The 13(R)-stereoisomer elutes before the 13(S)-stereoisomer. Elution times may vary. (C) CP-HPLC of peak 3 from A. The 9(S)-stereoisomer elutes before the 9(R)-stereoisomer. Elution times may vary.

Frankel, E.N. and Gardner, H.W. 1989. Effect of a-tocopherol on the volatile thermal decomposition products of methyl linoleate hydroperoxides. Lipids 24 603-608. 

Aldehyde Formation. Several investigators observed a marked dominance of hexanal in the volatile products of low-temperature oxidation. At the higher temperatures, however, 2,4-decadienal was the major aldehyde formed (19,20,21). Both aldehydes are typical scission products of linoleate hydroperoxides. Swoboda and Lea (20) explained this difference on the basis of a selective further oxidation of the dienal at the higher temperature, while Kimoto and Gaddis (19) speculated that the carbon-carbon bond between the carbonyl group and the double bond (Type B) is the most vulnerable to cleavage under moderate conditions of autoxidation, while scission at the carbon-carbon bond away from the olefinic linkage (Type A) is favored under stress such as heat or alkali. 

Interactions with Histidine. Imidazole lactic acid and imidazole acetic acid were identified as breakdown products when histidine was reacted with methyl linoleate, methyl linoleate hydroperoxide or hexanal for 3 weeks at 25°C and 51°C (33). It was postulated that these compounds were formed via free radical reactions. Two other products were also produced which yielded histidine upon acid hydrolysis. These were thought to be Schiff s base compounds arising... 

Direct Measurements—UVNIS Techniques. The conjugated diene (CD) formed among the polyene hydroperoxide products that are formed as a result of oxidation of polyunsaturated fatty acids (PUFAs) have a UV absorbance that can be monitored to follow the progress of the oxidation. The effect of antioxidants on the suppressed rate of product formation can be followed with time. For example, conjugated dienes from oxidation of linoleate lipid molecules absorb at 234 nm and can be monitored directly , or else after HPLC separation (via normal phase or reverse phase j of the individual isomers. In order to use these findings to calculate the antioxidant activity of phenols and relate it to oxygen uptake studies (equations 7 and 14), one also has to make a correction to account for loss of absorbance due to loss (from decomposition) of hydroperoxides (equation 22) . 

Reactive aldehydes derived from lipid peroxidation, which are able to bind to several amino acid residues, are also capable of generating novel amino acid oxidation products. By means of specific polyclonal or monoclonal antibodies, the occurrence of malonaldehyde (MDA) and 4-hydroxynonenal (4-HNE) bound to cellular protein has been shown. Lysine modification by lipid peroxidation products (linoleic hydroperoxide) can yield neo-antigenic determinants such as N-c-hexanoyl lysine. Both histidine and lysine are nucleophilic amino acids and therefore vulnerable to modification by lipid peroxidation-derived electrophiles, such as 2-alkenals, 4-hydroxy-2-alkenals, and ketoaldehydes, derived from lipid peroxidation. Histidine shows specific reactivity toward 2-alkenals and 4-hydroxy-2-alkenals, whereas lysine is an ubiquitous target of aldehydes, generating various types of adducts. Covalent binding of reactive aldehydes to histidine and lysine is associated with the appearance of carbonyl reactivity and antigenicity of proteins [125]. 

Recently St. Angelo et al. (38 ) presented data reaffirming their previous observation that hexanal is an enzymically produced volatile product of the peanut lipoxygenase-linoleic acid reaction. They also confirmed the observations of Pattee and co-workers (33) that pentane is present in the headspace volatiles from the reaction. St. Angelo et al. (38) further showed that care must be excerised to prevent pentane artifacts from arising from the known thermal degradation of hydroperoxide products (39) present in the aqueous solution. 

Cooxidation of cosubstrates requires the presence of both substrate (e.g., linoleic acid) and LOX—these cannot be replaced by the hydroperoxide product. Thus, cooxidation is part of (not subsequent to) the LOX reaction ... 

Many of the classical mechanistic concepts of lipid oxidation were formulated on the basis of kinetic studies. Later developments in support of the general free radical mechanism of oxidation were based on structural studies of the primary hydroperoxide products. To simplify the kinetics of linoleate oxidation, the reactions were studied at early stages of oxidation, at low levels of conversion, at lower temperatures and in the presence of an appropriate initiator. Under these conditions, the propagation reactions producing hydroperoxides in high yields are emphasized, and the decomposition of hydroperoxides is minimized... 

As with oleate, some volatile decomposition compounds are formed from linoleate hydroperoxides that cannot be explained by the classical A and B cleavage mechanism, including acetaldehyde, 2-pentylfuran, methyl heptanoate, 2-octenal, 2,4-nonadienal, methyl 8-oxooctanoate, and methyl 10-oxodecanoate. Although hydroperoxides derived from both autoxidation and from photosensitized oxidation of linoleate form the same volatile decomposition products, significant quantitative differences are noted. The autoxidized linoleate hydroperoxides produced more pentane, 2-pentyl furan, 2,4-decadienal and... 

Lingnert and Eriksson (1981), (2)Eicher(1981), (3) Kim and Harris (1989)(4) Alaizelol. (1999), (5) Mastrocola and Munari (2000), (Q ling and Kitts (2002), (7) Dittrich et al. (2003). Abbreviations PV, peroxide value MRP, Maillard reaction products BSA, bovine serum albumin MeLo-OOH, methyl linoleate hydroperoxides TEARS, thiobarbituric reactive substances ABAP, 2,2 -azo-bis(2-amidinopropane)dichloride DPPH, l,l-diphenyl-2-picrylhydrazyl LDL, low-density lipoproteins CD, conjugated dienes. 

The hydroperoxidation products of linoleic acid were studied by Wu and coworkers [662]. Ten products (e.g., 13-hydroxy-(9Z-l l )-octadeca-9,l 1-dienoic acid, 9-hydroxy-(10 -12E)-octadeca-10,12-dienoic acid, ketooctadecadienoic acid, hydroxyoctadecadienoic acid) were resolved in <30 min on a silica column (2 =234nm) using a 98/2/0.05 hexane/IPA/acetic acid mobile phase. Peak shapes were excellent and good resolution was obtained. The same conditions were used in semipreparative work. Structures were confirmed by GC/MS. 

Many secondary oxidation products of fatty acids have been shown to be more toxic to experimental animals. This is partly due to the fact that the low molecular weight products have shorter carbon chain lengths, and are more easily absorbed into the intestinal wall than lipid hydroperoxides or their polymeric materials. Oarada et al. (1986), for example, have shown that over 73% of radioactivity was found in the urine and CO2 of rats 12 h after receiving " C-labeled low molecular compounds, compared to less than 25% for methyl linoleate hydroperoxides and the polymeric fraction. 

Oarada, M., Miyazawa, T. and Kaneda, T. (1986) Distribution of " C after oral administration of [U- X] labeled methyl linoleate hydroperoxide and their secondary products in rats. Lipids 21, 150-154. 

Lipid hydroperoxides are either formed in an autocatalytic process initiated by hydroxyl radicals or they are formed photochemically. Lipid hydroperoxides, known as the primary lipid oxidation products, are tasteless and odourless, but may be cleaved into the so-called secondary lipid oxidation products by heat or by metal ion catalysis. This transformation of hydroperoxides to secondary lipid oxidation products can thus be seen during chill storage of pork (Nielsen et al, 1997). The secondary lipid oxidation products, like hexanal from linoleic acid, are volatile and provide precooked meats, dried milk products and used frying oil with characteristic off-flavours (Shahidi and Pegg, 1994). They may further react with proteins forming fluorescent protein derivatives derived from initially formed Schiff bases (Tappel, 1956). 

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