Linoleic acid PUFAs

As mentioned earlier, both MCTs and LCTs are used in tube feeding products. Corn, soy, and safflower oils have been the mainstay sources of fat in these products, providing mainly co-6 polyunsaturated fatty acids (PUFAs). On the other hand, some newer EN products contain higher quantities of co-3 PUFAs from sources such as fish oil [i.e., docosahexenoic acid (DHA) and eicosapentenoic acid or (EPA)]. Still other formulas contain higher quantities of monounsaturated fatty acids from canola oil and high-oleic safflower or sunflower oils. The essential fatty acid (EFA) content (mainly linoleic acid) of EN... 

Dietary polyunsaturated fatty acids (PUFAs), especially the n-3 series that are found in marine fish oils, modulate a variety of normal and disease processes, and consequently affect human health. PUFAs are classified based on the position of double bonds in their lipid structure and include the n-3 and n-6 series. Dietary n-3 PUFAs include a-linolenic acid, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) whereas the most common n-6 PUFAs are linoleic acid, y-linolenic acid, and arachidonic acid (AA). AA is the primary precursor of eicosanoids, which includes the prostaglandins, leukotrienes, and thromboxanes. Collectively, these AA-derived mediators can exert profound effects on immune and inflammatory processes. Mammals can neither synthesize n-3 and n-6 PUFAs nor convert one variety to the other as they do not possess the appropriate enzymes. PUFAs are required for membrane formation and function... 

About 40 different fatty acids occur naturally. Palmitic acid (Ci6) and stearic acid (Cis) are the most abundant saturated acids oleic and linoleic acids (both G ) are the most abundant unsaturated ones. Oleic acid is monounsaturated because it has only one double bond, but linoleic and linolenic acids are polyunsaturated fatty acids (called PUFAs) because they have more than one carbon-carbon double bond. Although the reasons are not yet clear, it appears that a diet rich in saturated fats leads to a higher level of blood cholesterol and consequent higher risk of heart attack than a diet rich in unsaturated fats. 

Thus, 26 molecules of linoleic acid undergo autoxidation when a single free radical is introduced into this model membrane system (96). That much damage might well be enough to destroy the membrane and produce cell lysis and death however, we must remember that in the real system, the polyunsaturated fatty acids (PUFA) would be protected by antioxidants such as vitamin E. 

CLA refers to a mixture of positional and geometric isomers of linoleic acid (cis-9, cis-12 octadecadienoic acid) with a conjugated double bond system. The structure of two CLA isomers is contrasted with linoleic and vaccenic acids in Figure 3.1. The presence of CLA isomers in ruminant fat is related to the biohydrogenation of polyunsaturated fatty acids (PUFAs) in the rumen. Ruminant fats are relatively more saturated than most plant oils and this is also a consequence of biohydrogenation of dietary PUFAs by rumen bacteria. Increases in saturated fatty acids are considered undesirable, but consumption of CLA has been shown to be associated with many health benefits, and food products derived from ruminants are the major dietary source of CLA for humans. The interest in health benefits of CLA has its genesis in the research by Pariza and associates who first demonstrated that... 

The products obtained from the co-6 fatty acids (linoleic acid, y-linolenic acid, and arachidonic acid) by in vivo reactions with strain ALA2 contain diepoxy bicyclic structures, tetrahydrofuranyl rings, and/or trihydroxy groups in their molecules. In contrast to these co-6 PUFAs, substrates classified as co-3 PUFAs (a-linolenic acid, EPA, and DHA) are only converted to hydroxyl THFAs by strain ALA2 with no diepoxy bicyclic or trihydroxy derivatives uncovered to date. Both the hydroxyl groups and cyclic structures derived there from appear to be placed at the same positions on the substrates from the co-carbon termini within each PUFA class, despite differences in carbon chain length and the number of double bonds in the specific PUFA substrates. 

Chia oil is high in polyunsaturated fatty acids, particularly a-linolenic acid the content of this fatty acid is higher than flax oil (Table 4). Linoleic acid is the second-most abundant acid in chia with a contribution of 17-26%, which gives PUFA content of 83%, the highest amount among edible oils. Additionally, chia oil has the lowest content of saturated fatty acids (Tables 2 and 4). 

The typical sunflower oil composition is 66-72% linoleic acid, 12% saturated acids (palmitic and stearic), 16-20% oleic acid, and less than 1% a-linolenic acid. An increase in low-density lipoprotein cholesterol (LDL-C) and a decrease of high-density lipoprotein cholesterol (HDL-C) are believed risk factors of coronary heart disease (CHD). Diets rich in saturated fat increase plasma total and LDL-C. Traditional high-linoleic sunflower oil has always been regarded as healthy because of its high content of polyunsaturated fatty acids (PUFA) and relatively low content in saturated fatty acids. 

There is also controversy over the importance of MUFA over PUFA from the metabolic viewpoint. Great emphasis is placed on the distinction between the n-3 PUFA and those of the n-6 family. An increased intake of n-3 and a reduced intake of n-6 are recommended in light of the competitive metabolism of both families of fatty acids. As linoleic acid is a n-6 parent, a reduction of its intake favors the n-3/n-6 ratio on the other hand, it is also an essential fatty acid. 

The fatty acid composition of the extracts was not affected by temperature, pressure, and the extraction method (Table 4). Supercritical carbon-dioxide-extracted oil samples had similar fatty acid composition to that of the Soxhlet-extracted oil (Table 4). All of the wheat germ extracts consisted of about 56% linoleic acid (18 2 n-6), which is an essential fatty acid (Table 4). The total unsaturated and polyunsaturated fatty acid (PUFA) content of the wheat germ oil was about 81 % and 64%, respectively. The SC-CO2 extraction of wheat germ resulted in extracts with similar tocopherol and tocotrienol compositions to those of the Soxhlet extracts (Table 8) (50). These results indicate that SC-CO2 technology can be used for extraction and fractionation of WGO components to obtain products with high quality. 

Experiences in cat nutrition underscore the fallacy of assuming that metabolic pathways found in one species are automatically present in others. Early studies on metabolism of PUFA were conducted on rats, which have high A6 and A5 desa-turase abilities to convert linoleic acid (18 2n-6) to the prostaglandin precursors dihomo-y-linolenic acid (20 3 -6) and arachidonic acid (20 4 -6), respectively. This led to the assumption that other species can desaturate polyunsaturated fatty acids equally well. Over a period of time, it was shown that cats are not able to convert 18 2 -6 to 20 3n-6 or 20 4 -6. The NRC currently recommends the inclusion of 5 g linoleic acid and 0.2 g arachidonic acid/kg diet dry matter. 

When compared to 12 0, 14 0, and 16 0, oleic acid (18 1) or linoleic acid (18 2) provokes a drop in LDl- CholesteroI of about 15%, When directly comparing monounsaturated fatty acids with FUFAs, one finds that ntonounsaturated fatty acids seem to raise plasma TG levels, A slight increase in plasma TG may occur with the oleic add. in addition, PUFAs seem to be more consistent at raising HDLoleic acid. In these respects PUFAs may be more desirable than monounsaturated fattv adds (Kris-Etherton and Yu, 1997),... 

Dietary PUFAs decrease the plasma LDL-cholesterol level. Vegetable oils contain high levels of PUFAs such as linoleic acid (18 2), which constitutes about 25, 50, 63, and 75% of the fatty acids in peanut, soy, sunflower, and safflower oils, respectively. The quantity of 18 2 in beef and pork fat is only 5-10% and is under 3% in tropical oils. PUFAs produce decreases in LDL-cholesterol, possibly by the same (unknown) mechanism as monounsaturates. The question of whether dietary PUFAs have a greater or similar effect on LDL-cholesterol remains rmsettled. 

The next study is purely chemical in nature and concerns the relationship between vitamin E and PUFAs. The study traces the breakdown of PUFAs over time. Layers of linoleic acid were placed in dishes. One dish contained a layer consisting only of linoleic acid (, Figure 9.107). Another dish contained a mixture of linoleic acid and vitamin E, with one molecule of vitamin E per 2(X)0 molecules of the fatty acid (-0—). A third dish contained a greater proportion of vitamin E, one molecule of vitamin E per 400 molecules of linoleate (—O—). The dishes were stored in air for 9 hours and samples taken at the times indicated in Figure 9.107. The results show the protective effect of vitamin E. Damage to the PUFA commenced immediately where the layer did not contain the vitamin. The damage was delayed where increasing concentrations of the vitamin had been included. 

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