Polyunsaturated fatty acids major sources

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... 

Fig. 13.12 Polyunsaturated fatty acids required for eicosanoid synthesis. Oleic acid is the only fatty acid synthesized by mammals de novo. Linoleic (co-3) and a-linolenic acid (9 or greater fatty acids. Ingested o>3 fatty acids are metabolized to other co-3 fatty acids with o>9 double bonds. The same applies to co-6 fatty acids. The major dietary sources of polyunsaturated fatty acids are fish and plants oils...

Other studies have indicated that PG and PLD are a major source of PA in cells stimulated with various agonists [197-200] and several studies have confirmed biphasic formation of DAG, with the first phase derived from PIP2 and the second from PC via PA [201-205]. Analyses of the specific fatty acid composition of PA and PtdBut derived from cells treated with butanol and stimulated by bombesin or LPA also showed a predominance of saturated and mono-unsaturated fatty acids in the lipids derived from PLD action [206]. The fatty acid composition was very different from that found in DAG generated by PLC action on PIP2, in which polyunsaturated fatty acids predominate. The key issue is whether the DAG species derived from PC can activate PKC. Although studies indicate that this species is active on PKC in vitro, this has not been demonstrated in vivo. As described above [196], PC-derived DAG can activate Ca +-independent PKC isozymes but, because of the lack of a Ca rise, it cannot activate ( a -dcpcridcril PKC isozymes. 

The endoplasmic reticulum (ER) has traditionally been viewed as the primary source of phospholipids in plant cells. With the exception of cardiolipin, all of the common phospholipids can be produced by microsomal fractions. The ER also serves as the major site of fatty acid diversification. Although plastids do have the ability to synthesize polyunsaturated fatty acids, they are formed on acyl lipid substrates and are not typically exported. Thus, the ER desaturation pathways are of particular importance for developing seeds that store large quantities of 18 2 and 18 3. Pathways for the production of unusual fatty acids found primarily in seed oils have likewise been described in microsomes. Not surprisingly, the ER also appears to be instrumental in the formation of TGs and the lipid bodies in which they are stored (Section 7). 

The United States currently produces over 3.1 billion bushels of soybeans per year (The American Soybean Association, 2007). In 2006, over one-third (1.1 billion bushels) of the crop was exported, while the remainder was sold on the domestic market. Of the edible soybean products in the U.S. market, the consumption of soybean oil (SBO) is greatest U.S. production of SBO has surpassed 20 billion pounds per year (The American Soybean Association, 2007). SBO is the major edible oil in the United States and represented 75% of the total edible oils and fats consumed in 2006. The predominant dietary sources of SBO are salad and cooking oil (48%) and baking and frying fats (34%). SBO has a unique fatty acid profile it is comprised predomi-nandy of unsaturated fatty acids including monounsaturated fatty acids (MU FA) and polyunsaturated fatty acids (PUFA), of which the predominant PUFA is linoleic acid (LA), and to a much lesser extent, a-linolenic acid (ALA). 

The mammary gland produces milk, which is the major source of nutrients for the breastfed human infant. The fatty acid composition of human milk varies, depending on the diet of the mother. However, long-chain fatty acids predominate, particularly palmitic, oleic, and linoleic acids. Although the amount of fat contained in human milk and cow s milk is similar, cow s milk contains more short- and medium-chain fatty acids and does not contain the long-chain, polyunsaturated fatty acids found in human milk that are important in brain development. 

Fig. 1. Proposed resolution of the n-3 paradox [modified from Budowski (35)]. Phagocytic leukocytes are a major source of the reactive oxygen species that are implicated in the pathogenesis of atherosclerotic disease. The n-3 long-chain polyunsaturated fatty acids (LC-PUFA) attenuate phagocytic leukocyte activity by acting as antioxidants.

Conjugated linoleic acid (CLA) is naturally present in milk, dairy products, and the meat of ruminants (1). Ruminants are the major dietary source of this fatty acid because of the unique abihty of rumen bacteria to convert linoleic acid into cis-9,trans- CLA (c9,tll-CLA) (1). This reaction is part of a process that takes place in the rumen it is called biohydrogenation and it converts linoleic acid [or, less efficiently, other 18-carbon polyunsaturated fatty acids (PUFA) with double bonds located at 9 and 12 positions] to stearic acid (1). During this process, vaccenic acid (tl 1-18 1) is formed. This acid can be converted to CLA in all organisms that possess A9-desaturase (2). 

Oleate desaturase expression by antisense RNA in soybean led to an oil containing over 80 % oleic acid as compared to a normal 23 %, with significant decrease in polyunsaturated fatty acids [155]. Ganoladoes not normally accumulate capric and caprylic acids. But the introduction of the Cuphea hookeriana acyl-AGP thioesterase cDNA in canola resulted in the accumulation of these two medium-chain fatty acids in the seeds [156]. In plants, 0)-6 desaturase-catalyzed pathway in the microsomes is a major source of polyunsaturated lipids, introduction of the... 

Thus, it can be concluded that yeasts, in general, exhibit rather conservative patterns of fatty acyl distributions. The vast majority of yeasts produce only Ci6 and Cig fatty adds. The principal saturated fatty acid is always palmitic acid the principal unsaturated fatty acid is oleic acid except for a few species where 16 1 abounds. Di- and polyunsaturated fatty acids are usually present. Contents of 18 2 may occasionally equal that of 18 1 but 18 3 is usually only a minor component. For the possible exploitation of yeasts as sources of fatty acids, the target oil has therefore to be selected with care (see below). 

Specific sources of vitamin E (ctlphn-tocopherol) include carrots, squash, broccoli, sweet potatoes, tomatoes, kale, cantaloupe melon, peaches and apricots. Vitamin E (Figure 9.19) is the main lipid-soluble antioxidant. It occurs in cell membranes together with polyunsaturated fatty acids in phospholipids, and vegetable oils (especially those rich in polyunsaturated fatty acids) are a major dietary source. It is a phenolic antioxidant, as are most natural antioxidants. 

Fish with high fat contents is an important source of long-chain n-3 polyunsaturated fatty acids (PUFAs) in the human diet, in particular for docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) (EFSA, 2005). On the other side, a wide range of environmental contaminants have been reported to be accumulated in fish that can pose a potential human health hazard (Leonard, 2011). Major contaminations include the different OCPs, PAHs or the widely distributed persistent organic pollutants (POPs) with the polychlorinated biphenyls (PCBs) and the flame retardants compound class of the polybrominated diphenylethers (PBDEs). Also farmed fish can significantly contribute to dietary exposure to various contaminants due to the use of land sourced fish feed. A multi method for efficient control of fish and fish feed for various groups of contaminants from PCBs, OCPs, BFRs (brominated flame retardants) and PAHs is outlined in the following analytical procedure published by Kamila Kalachova et al. (Kalachova et al., 2013). 

Fatty acid desaturation, a second major source of variation in the phylogenetic distribution of fatty acids, has been reviewed in detail (294-302). Some bacteria have a unique anaerobic system for production of monounsaturated fatty acids. This mechanism is involved in elongation of medium-chain length c/.r-3-unsaturated fatty acyl intermediates, and functions via P,y-dehydration of P-OH intermediates. It should be noted that this process cannot generate methylene-interrupted polyunsaturated fatty acids. 

The major polyunsaturated fatty acids all contain cis methylene interrupted sequences and for years it was thought that most conjugated systems were artefacts of isolation. However, many such acids have now been firmly identified and are found in sources as diverse as seed oils, some microorganisms and some marine lipids (especially sponges). An example of one such acid would be a-eleostearic acid (Table 3.3). 

Polyunsaturated fatty acids are ultimately derived from plants, seed, leaves, and phytoplankton. Terrestrial food chains (i.e., edible plants and animal fat) contain primarily linoleic acid (Table 3, Fig. 2), an polyunsaturated fatty acid, and only very small amounts of cu-3 polyunsaturated fatty acids (nearly exclusively CK-linolenic acid). Fatty acids in land plants are not chain-elongated above the 18-carbon level. In mammalians, the polyunsaturated 18-carbon eu-6 linoleic acid will be converted to arachidonic acid (20 4, (o-6) by chain elongation and desaturation. As the three major families of unsaturated fatty acids (oleic acid, (o-9 linoleic acid, cu-6 and linolenic acid, cu-3) (Table 3) are metabolically nearly inconvertible in mammalians, phytoplankton and algae, which synthesize eicosapentaenoic acid (20 5, cu-3) and docosahexaenoic acid (22 6, cu-3), are the principal sources of the major cu-3 fatty acids. Only a-linolenic acid from vegetable oils is in principle able to be partially converted to eicosapentaenoic acid ([26] Fig. 2). 

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