Oxidation products, lipids

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

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). 

Interaction of lipid oxidation products and amino compounds. Amino acids and primary amines may be involved in other reactions which could lead to the formation of compounds having the potential to undergo N-nitrosation. Malonaldehyde, produced as a result of oxidation of lipids, particularly polyunsaturated fatty acids, has been shown to react with amino acids to produce... 

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... 

Addis, P.B. and Warner, G.J. (1991). The potential health aspects of lipid oxidation products in food. In Free Radicals and Food Additives (eds. O.I. Aruoma and B. Halliwell) pp. 77-119. Taylor and Francis, London. 

Hidalgo FJ, Zamera R (2004) Strecker-type degradation produced by the lipid oxidation products 4, 5 epoxy-2-alkenals. J Agri Food Chem 52 7126-7131... 

Nilzen V, Babol J, Dutta P C, Lundeheim N, Enfalt A-C and Lundstrom K (2001), Free range rearing of pigs with access to pasture grazing-effect on fatty acid composition and lipid oxidation products , Meat Sci, 58, 267-275. 

Studies carried out with complete cells in vivo, cell membranes and other cell fractions point to the selective oxidation of phosphatidylserine (26) to a hydroperoxide (PS-OOH) on oxidative stress caused by toxic agents such as H2O2, t-BuOOH and cumyl hydroperoxide (27). Formation of PS-OOH is observed during apoptosis. These phenomena are important because of the cytotoxic effects of various peroxides used in commercial products coming into direct contact with the human body, as is the case of epidermal keratinocytes in contact with cosmetic formulations" ". The toxic effects of f-BuOOH are associated with vasoconstriction and damage to the vascular smooth muscles ". Global determination methods for primary lipid oxidation products are discussed in Section IV.B. 

The oxidation hypothesis of atherosclerosis states that the oxidative modification of LDL (or other lipoproteins) is important and possibly obligatory in the pathogenesis of the atherosclerotic lesion thus, it has been suggested that inhibiting the oxidation of LDL will decrease or prevent atherosclerosis and clinical sequelae. LDL oxidation also has important implications for vascular health function. High concentrations of LDL may inhibit arterial function in terms of the release of nitric oxide from the endothelium and many of these effects are mediated by lipid oxidation products. Furthermore, oxidized LDL inhibits endothelium-dependent nitric oxide-mediated relaxations in isolated rabbit coronary arter-... 

Zhou, S. and Decker, E. A. (1999). Ability of amino acids, dipeptides, polyamines, and sulfhydryls to quench hexanal, a saturated aldehydic lipid oxidation product. ]. Agric. Food Chem. 47,1932-1936. 

D2.2 Chromatographic Analysis of Secondary Lipid Oxidation Products... 

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... 

Table D2.2.1 lists a number of problems that might arise in headspace chromatography of lipid oxidation products, along with their possible causes and solutions.

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