Linoleic acid data

TABLE 6. Isomerization of 13-OOH to 9-OOH and Corresponding Shift in Products During Heating of Linoleic Acid. Data from (297). 

Figure 9. Typical initial scission patterns of oxidizing linoleic acid. Data from (340, 341). Parentheses indicate unstable intermediates brackets denote products from secondary...

Belkner et al. [32] demonstrated that 15-LOX oxidized preferably LDL cholesterol esters. Even in the presence of free linoleic acid, cholesteryl linoleate continued to be a major LOX substrate. It was also found that the depletion of LDL from a-tocopherol has not prevented the LDL oxidation. This is of a special interest in connection with the role of a-tocopherol in LDL oxidation. As the majority of cholesteryl esters is normally buried in the core of a lipoprotein particle and cannot be directly oxidized by LOX, it has been suggested that LDL oxidation might be initiated by a-tocopheryl radical formed during the oxidation of a-tocopherol [33,34]. Correspondingly, it was concluded that the oxidation of LDL by soybean and recombinant human 15-LOXs may occur by two pathways (a) LDL-free fatty acids are oxidized enzymatically with the formation of a-tocopheryl radical, and (b) the a-tocopheryl-mediated oxidation of cholesteryl esters occurs via a nonenzymatic way. Pro and con proofs related to the prooxidant role of a-tocopherol were considered in Chapter 25 in connection with the study of nonenzymatic lipid oxidation and in Chapter 29 dedicated to antioxidants. It should be stressed that comparison of the possible effects of a-tocopherol and nitric oxide on LDL oxidation does not support importance of a-tocopherol prooxidant activity. It should be mentioned that the above data describing the activity of cholesteryl esters in LDL oxidation are in contradiction with some earlier results. Thus in 1988, Sparrow et al. [35] suggested that the 15-LOX-catalyzed oxidation of LDL is accelerated in the presence of phospholipase A2, i.e., the hydrolysis of cholesterol esters is an important step in LDL oxidation. 

In contrast to numerous literature data, which indicate that protein oxidation, as a rule, precedes lipid peroxidation, Parinandi et al. [66] found that the modification of proteins in rat myocardial membranes exposed to prooxidants (ferrous ion/ascorbate, cupric ion/tert-butyl-hydroperoxide, linoleic acid hydroperoxide, and soybean lipoxygenase) accompanied lipid peroxidation initiated by these prooxidant systems. 

Study, no increase in tissue CLA was found in rats fed linoleic acid fortified diets (Chin, S. F. and M. W. Pariza, University of Wisconsin-Madison, unpublished data), indicating that the bacterial flora of rats is capable of converting linoleic acid to cis-9, trans-11 CLA. Further study is needed to identify the bacteria responsible for this effect. 

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). 

Firstly, I will discuss recent evidence supporting the hypothesis that free radicals contribute to important chronic diseases in man and exert an important life-shortening effect. Secondly, I will review data on the toxicity of lipid hydroperoxides and their decomposition products, since lipid hydroperoxides can be a source of free radicals in vivo. And lastly, I will review a system under study in our laboratory in which quantitative data on lipid peroxidation and antioxidants is being obtained using linoleic acid in SDS micelles. 

Barrefors et al. (1995) analyzed samples with and without oxidized flavor from two commercial herds. Their data indicated that oxidized milk samples had a higher linoleic acid content in the neutral fat fraction and contained a higher concentration of hexanal. At one of the farms, the concentration of both a-tocopherol and (3-carotene were lower in samples that developed off-flavor. They speculated that high-yielding cows fed high amounts of unsaturated fats in their feed needed higher dietary concentrations of a-tocopherol and (3-carotene. 

This data demonstrates a degree of additivity in effect upon particle diameter between substances which easily form free radicals and linoleic acid containing an active methylene group which can give up hydrogen readily to produce a radical. All of these substances are efficient retarders of the polymerization rate. 

Table 10.2 lists the structure and melting point of four fatty acids containing 18 carbon atoms. Stearic acid is one of the two most common saturated fatty acids, and oleic and linoleic acids are the most common unsaturated ones. The data show the effect of Z double bonds on the melting point of fatty acids. 

The predominant pair of these ten types includes palmitic acid as the saturated acid in acyl positions 1 and 3, whereas position 2 is occupied by oleic or linoleic acid. This is illustrated in position distribution data from Jurriens and Kroesen (73) that indicates the middle acyl position was occupied by linoleic acid 64.3% of the time. 

Analysis performed on varieties of flaxseeds collected from different flax growing regions of the world and later grown in Morden, Manitoba, Canada, showed even wider distributions of oleic acid 14-60%, linoleic acid 3-21%, and ALA 31-72% (13). All of these data indicate that within flax, there is a wide distribution of fatty acids, and this variability can be used for developing specialty oils based on traditional breeding and to avoid GMO oils. 

The seed oils from African pumpkin (squash) (Cucurbita pepo L.) were evaluated for their fatty acid profiles and the presence of other phytochemicals (53). The seed oils contained 28-36% oleic acid. The primary fatty acid was linoleic acid, along with palmitic and stearic acids, with a total unsaturated fatty acid concentration of 77-83%. Alpha-tocopherol was determined at a concentration up to 3.0 mg/ 100 g. These data suggest that pumpkin seed oil may be a better choice for consumers who prefer high unsaturation, or both linoleic and oleic acids. Seed oils from species of Cucurbita with minimal pericarp, called naked seed squash, are discussed below. 

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