Peroxide breakdown products

More recently, B. Goldstein and McDonagh demonstrated that the native protein fluorescence (280-nm excitation, 330-nm emission) of red-cell membranes exposed in vitro to ozone at 1 ppm was a somewhat more sensitive indicator of ozone effect than other characteristics measured in the same em, including oxidation of cell-membrane sulfhydiyl groups, loss of acetylcholinesterase activity, and formation of lipid peroxide breakdown products. 

Dowell et al. reported an increase in the osmotic fragility of alveolar macrophage preparations obtained horn rabbits acutely exposed to ozone at 10 ppm for 3 h or intermittently exposed to ozone at 2 ppm for 8 h/day for 7 days. Similar intermittent exposure to ozone at 0.5 ppm was without effect. A test for malonaldehyde formation was negative, but this lipid peroxide breakdown product may have been lost during the preparatory procedure. 

ONOO ), reduced transition metals (Cn, Fe), and the by-prodncts of hpid and free attuno acid oxidation. Oxidizing species directly attack the Cys and Met residues. Metals generally chelate with histidine, while Lys, Arg, Pro, and Thr form carbonyl groups on side chains. Indirect protein oxidation occurs with hpid peroxidation breakdown products such as 4-HNE and MDA, which add to Lys, His, and Cys residnes. 

THF is available unstabilized, or stabilized with 25 ppm (typical for GC use) to 250 ppm (typical for HPLC use) butylated hydroxytoluene (BHT 2,6-di-r-butyl-p-cresol), which is added to scavenge the peroxide breakdown products of THF. Ethyl ether can be purchased unstabilized or stabilized with ethanol ( 2-3%), BHT (1-10 ppm), or a blend of ethanol, water, and BHT (1.5-3.5%, 0.2-0.5%, and 5-10 ppm, respectively). Isopropyl ether is available unstabilized or stabilized widi 0.01% hydroquinone or 5-100 ppm BHT. Dioxane is available unpreserved or with 25-1500 ppm BHT as preservative. From the above, it is important that the correct solvent be chosen for use, since most are available unstabilized or stabilized and with a range of stabilizers and stabilizer concentrations. 

Addition of quercetin to culture cell medium enhanced the rate of growth of baby hamster kidney (BHK-21) cells and also diminished levels of Upid peroxidation breakdown products [214]. Furtoermore, quercetin and three other flavonoids, hesperetin, naringenin, rutin, were found to be effective inhibitors of lipid oxidation in two different in vitro experimental models (1) Fe( )-induced linoleate peroxidation, by detection of conjugated dienes, and (2) auto-oxidation... 

Alliangana DM. Effects of beta-carotene, flavonoid quercitin and quinacrine on cell proliferation and lipid peroxidation breakdown products in BHK-21 cells. East Afr Med J 1996 73 752-757. 

Oxidation begins with the breakdown of hydroperoxides and the formation of free radicals. These reactive peroxy radicals initiate a chain reaction that propagates the breakdown of hydroperoxides into aldehydes (qv), ketones (qv), alcohols, and hydrocarbons (qv). These breakdown products make an oxidized product organoleptically unacceptable. Antioxidants work by donating a hydrogen atom to the reactive peroxide radical, ending the chain reaction (17). 

Measuring the content of primary oxidation products is limited due to the transitory nature of peroxides. Yet, their presence may indicate a potential for later formation of sensorially objectionable compounds. The peroxide content increases only when the rate of peroxide formation exceeds that of its destruction. In cases where peroxide breakdown is as fast as or faster than peroxide formation, monitoring lipid peroxides is not a good indicator of oxidation. This can occur in frying oils and sometimes in meat products, particularly in cooked meats where iron is very active and peroxide breakdown is quite rapid. Because the acceptability of an oil or lipid-containing food product depends on the degree to which oxidation has progressed, the simultaneous detection of primary and secondary lipid oxidation products helps to better characterize lipid quality. It is... 

Cleavage of the carbon bonds during lipid peroxidation reactions results in the formation of aldehydic products such as cytotoxic alkanals and alkenals, as well as alkanes. The breakdown products of lipid peroxidation, alkanals such... 

Some analyses have shown that lipid peroxidation and the concentration of its breakdown products are relatively low in undifferentiated highly proliferating tumour cells [60,61 ] and it has been hypothesised that the products of lipid peroxidation such as HNE may play a central role in the down-regulation of cell proliferation. Recently the physiological levels of HNE have been reported and were found to range from 0.2 to 2.8 pM [62], These levels represent a steady-state level of HNE because it is continuously produced and rapidly catabolised by normal cells [63]. 

It has been suggested that measurement of the aldehydic breakdown products of lipid peroxidation is the most reliable indicator that the process has occurred in vivo in normal or pathological conditions (Esterbauer et al., 1988), but there is very little information as to the rate of production of these compounds in vivo (Yoshino et al., 1986 Tomita et al., 1987), or of their relative proportions. 

Cure system species, accelerators and their reaction products This class of additive can present problems as they are often thermally labile, reactive and, in some cases, have a degree of ionic character (e.g. zinc dithiocarbamate salts). In these cases LC-MS is a more appropriate technique than GC-MS. It is also easier to use LC-MS with a number of the approved food simulants as they can be injected directly into the instrument, being compatible with the mobile phase. In some cases the reaction products (e.g. aniline from diphenyl guanidine, and benzothiazole from thiazole and sulphonamide accelerators) are stable and so GC and GC-MS can be used. Peroxides are popular curatives for food use rubbers and the stable, breakdown products of these can be easily detected by GC-MS. 

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