Lipid oxidation system

Radical-induced decomposition is thermodynamically favorable (Ea = 37.5 kCal), and is also more consistent with the characteristics of bimolecular initiation by hydroperoxides originally proposed by Russell (356), the kinetics measured in lipid oxidation systems, and significant epoxide products reported in many studies. Most importantly, the radical-induced decomposition described in Reaction 63 provides a powerful cascade of reactive radicals to fuel the very rapid increase in oxidation during the bimolecular rate period. 

Figure 10 summarizes some results of the lipid-oxidation system in basldlomycetes, leaves, fruits, vegetables, and cereals. It can be seen that there is a development with evolution and differentiation. The enzyme system is highly substrate specific to a (Z,Z)-1,4-pentadiene system converting linoleic- and linolenic acids into carbonyls and oxoacids which may undergo further isomerization (E3) and/or reduction (E4). Some of the components formed are very potent aromatics, pheromones, and wound hormones. Basidio-mycetes and Fungi produce (-)-1-octen-3-ol as their sensorial principle. 9-Oxodecanoic acid is known as queen substance and is the sex pheromone of honey bees. 

Figure 10. Lipid-oxidation system in basidiomycetes, leaves, fruits, vegetables,...

The EO of Crithmum maritimum (=Cachrys maritima, Apiaceae, rock samphire) comprises limonene and y-terpinene with an amount of 22.3% and 22.9%, respectively, as the major components. Two different test methods (TBA assay and a micellar model system where the antioxidative activity in different stages of the oxidative process of the lipid matrix was monitored) were used. Both assays explain the very high activity of this EO. In the TBA assay BHT and a-tocopherol were used as positive standards and the oil showed a better capacity than those substances. Comparable results were obtained by the micellar method system where the EO acts as a protector of the oxidation of linoleic acid and inhibits the formation of conjugated dienes (Ruberto et al., 2000). The modification of LDL by an oxidative process for instance can lead to atherosclerosis. Natural antioxidants such as P-carotene, ascorbic acid, a-tocopherol, EOs, and so on are able to protect LDL against this oxidative modification. y-Terpinene proved itself to be the strongest inhibitor of all used authentic compounds for the formation of TBARS in the Cu -induced lipid oxidation system (Grassmann et al, 2003). So, the addition of y-terpinene to food can possibly stop the oxidative modification of LDL and reduce the atherosclerosis risk. 

Park, E. Y. Murakami, H. Matsumura, Y. (2005). Effects of the addition of amino acids and peptides on lipid oxidation in a powdery model system. Journal of Agricultural and Food Chemistry, Vol. 53, No. 21, (September 2005), pp. 8334-8341 7, ISSN 0021-8561. 

Meat products have to be stabilised in some cases, as meat lipids contain no natural antioxidants or only traces of tocopherols. Most muscle foods contain, however, an efficient multi-component antioxidant defence system based on enzymes, but the balance changes adversely on storage. The denaturation of muscle proteins is the main cause of the inbalance as iron may be released from its complexes, catalysing the lipid oxidation. Salting contributes to the negative effects of storage, as it enhances oxidation. Using encapsulated salt eliminates the deleterious effect of sodium chloride. 

SEVERINI c and lerici c r (1995) Interaction between Maillard reaction and lipid oxidation in model systems during high temperature treatment , Ital J Food Sci, 1 (2) 189-96. 

Fig. 16.1 Progression of oxidation in a food system from formation of radicals through primary and secondary lipid oxidation products to protein damage.

Interestingly, early examples of carotenoid autoxidation in the literature described the influence of lipids and other antioxidants on the autoxidation of carotenoids." " In a stndy by Budowski et al.," the influence of fat was fonnd to be prooxidant. The oxidation of carotenoids was probably not only cansed by molecnlar oxygen bnt also by lipid oxidation products. This now well-known phenomenon called co-oxidation has been stndied in lipid solntions, in aqueons solntions catalyzed by enzymes," and even in food systems in relation to carotenoid oxida-tion." The inflnence of a-tocopherol on the antoxidation of carotenoids was also stndied by Takahashi et al. ° who showed that carotene oxidation was snppressed as... 

Extensive studies in vitro from many groups have confirmed that exposure of LDL to a variety of pro-oxidant systems, both cell-free and cell-mediated, results in the formation of lipid hydroperoxides and peroxidation products, fragmentation of apoprotein Bioo, hydrolysis of phospholipids, oxidation of cholesterol and cholesterylesters, formation of oxysterols, preceded by consumption of a-tocopherol and accompanied by consumption of 8-carotene, the minor carotenoids and 7-tocopherol. 

B Chronic hyperlipidemia and chronic infection potentiate inflammation and lipid oxidation. An increase of lipid oxidation might inhibit tbe immune system and thus facilitate a chronic infection and a rise in oxLDL-mediated apoptosis. 

Kolakowska, A. (2002). Lipid oxidation in food systems, in Sikorski, Z.E. and Kolakowska, A., eds., Chemical and Functional Properties of Food Lipids, CRC Press, Boca Raton, 133-166. 

The major phytotoxic components of the photochemical oxidant system, discussed in Chapter 11, are ozone and peroxyacetylnitrate (PAN), but there is indirect evidence that other phytotoxicants are present. Con siderable effort has gone into controlled exposures to ozone and into field studies. Leaf stomata are the principal sites for ozone and PAN entry into plant tissue. Closed stomata will protect plants from these oxidants. Both ozone and PAN may interfere with various oxidative reactions within plant cells. Membrane sulfhydryl groups and unsaturated lipid components may be primary targets of oxidants. Young leaf tissue is more sensitive to PAN newly expanding and maturing tissue is most sensitive to ozone. Light is required before plant tissue will respond to PAN that is not the case with ozone. 

The formation of free radicals after lipid oxidation is known to play a key role in the deterioration of meat flavor 8, 23), Since proteins constitute a major portion of the muscle s composition, the relationship between chemically active radical species and decomposition of food flavor proteins and peptides needs to be studied in detail. Data has been presented showing the correlation of proteins with flavor (Figures 5 and 6). Data is now presented showing how soluble meat proteins change in an environment where free radicals are induced by a free-radical oxidation generating system or FROG (Figure 10). 

Antioxidant activity was also tested in a liver microsome system. In this study, mice were treated by oral intubation (2 times/wk) with 0.2 ml olive oil alone or containing CLA (0.1 ml), linoleic acid (0.1 ml), or dl-a-tocopherol (lOmg). Four weeks after the first treatment, liver microsomes were prepared and subsequently subjected to oxidative stress using a non-enzymatic iron-dependent lipid peroxidation system. Microsomal lipid peroxidation was measured as thiobarbituric acid-reactive substance (TBARS) production using malondialdehyde as the standard. It was found that pretreatment of mice with CLA or dl-a-tocopherol significantly decreased TBARS formation in mouse liver microsomes (p < 0.05) (Sword, J. T. and M. W. Pariza, University of Wisconsin, unpublished data). 

Haugen, E., Undeland, I. (2003) Lipid oxidation in herring fillets (Clupea harengus) during ice storage measured by a commercial hybrid gas sensor array system. J. Agric. Food Chem. 51 752-759. 

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