Fatty polyunsaturated

The intermediate m hydrogenation formed by reaction of the unsaturated ester with the hydrogenated surface of the metal catalyst not only can proceed to the saturated fatty acid ester but also can dissociate to the original ester having a cis double bond or to its trans stereoisomer Unlike polyunsaturated vegetable oils which tend to reduce serum cholesterol levels the trans fats produced by partial hydrogenation have cholesterol raising effects similar to those of saturated fats... 

Prostaglandins arise from unsaturated C20 carboxylic acids such as arachidonic acid (see Table 26 1) Mammals cannot biosynthesize arachidonic acid directly They obtain Imoleic acid (Table 26 1) from vegetable oils m their diet and extend the car bon chain of Imoleic acid from 18 to 20 carbons while introducing two more double bonds Lmoleic acid is said to be an essential fatty acid, forming part of the dietary requirement of mammals Animals fed on diets that are deficient m Imoleic acid grow poorly and suffer a number of other disorders some of which are reversed on feed mg them vegetable oils rich m Imoleic acid and other polyunsaturated fatty acids One function of these substances is to provide the raw materials for prostaglandin biosynthesis... 

Com oil s flavor, color, stabiHty, retained clarity at refrigerator temperatures, polyunsaturated fatty acid composition, and vitamin E content make it a premium vegetable oil. The major uses are frying or salad appHcations (50%) and margarine formulations (35%). 

Unfortunately, excess consumption of fatty foods has been correlated with serious human disease conditions. Effects on cardiovascular disease (95), cancer (96), and function of the immune system (97) have been shown. Numerous studies have been conducted to determine the effects of saturated, monounsaturated, and polyunsaturated fatty acids on semm cholesterol and more recently high density Hpoprotein (HDL) and low density Hpoprotein... 

Fig. 9. Saturated, monounsaturated, and polyunsaturated fatty acids in common oils, where His saturate I, monounsaturate and polyunsaturate (100).

Light and photosynthetic electron transport convert DPEs into free radicals of undetermined stmcture. The radicals produced in the presence of the bipyridinium and DPE herbicides decrease leaf chlorophyll and carotenoid content and initiate general destmction of chloroplasts with concomitant formation of short-chain hydrocarbons from polyunsaturated fatty acids (37,97). 

Food. Lecithin is a widely used nutritional supplement rich ia polyunsaturated fatty acids, phosphatidylcholine, phosphatidylethanolamine, phosphatidjhnositol, and organically combiaed phosphoms, with emulsifying and antioxidant properties (38). 

Enriched polyunsaturated fatty acids from highly refined TOFA. 

Homogeneous and heterogenous catalysts which selectively or partially hydrogenate fatty amines have been developed (50). Selective hydrogenation of cis and trans isomers, and partial hydrogenation of polyunsaturated moieties, such as linoleic and linolenic to oleic, is possible. 

AH the bis- and tri-unsaturated prostanoids display sensitivity to atmospheric oxygen similar to that of polyunsaturated fatty acids and Hpids. As a result, exposure to the air causes gradual decomposition although the crystalline prostanoids ate less prone to oxygenation reactions than PG oils or solutions. 

The fatty acids obtained from the process can be used directly or further manipulated for improved or modified performance and stabiUty. Hardening is an operation in which some fraction of the unsaturated bonds present in the fatty acids are eliminated through hydrogenation or the addition of H2 across a carbon—carbon double bond. This process was initially intended to improve the odor and color stabiUty of fatty acids through elimination of the polyunsaturated species. However, with the growth in the use of specialty fatty acids, hydrogenation is a commercially important process to modify the physical properties of the fatty acids. 

Polyunsaturated fatty acids in vegetable oils, particularly finolenic esters in soybean oil, are especially sensitive to oxidation. Even a slight degree of oxidation, commonly referred to as flavor reversion, results in undesirable flavors, eg, beany, grassy, painty, or fishy. Oxidation is controlled by the exclusion of metal contaminants, eg, iron and copper addition of metal inactivators such as citric acid minimum exposure to air, protection from light, and selective hydrogenation to decrease the finolenate content to ca 3% (74). Careful quality control is essential for the production of acceptable edible soybean oil products (75). 

Sulfated Natural Oils and Fats. Sulfated natural triglycerides were the first nonsoap commercial surfactants introduced in the middle of the nineteenth century. Since then sulfates of many vegetable, animal, and fish oils have been investigated (see also Fats AND FATTY oils). With its hydroxyl group and a double bond, ricinoleic acid (12-hydroxy-9,10-octadecenoic acid) is an oil constituent particularly suited for sulfation. Its sulfate is known as turkey-red oil. Oleic acid is also suited for sulfation. Esters of these acids can be sulfated with a minimum of hydrolysis of the glyceride group. Polyunsaturated acids, with several double bonds, lead to dark-colored sulfation products. The reaction with sulfuric acid proceeds through either the hydroxyl or the double bond. The sulfuric acid half ester thus formed is neutralized with caustic soda ... 

The prostaglandins (qv) constitute another class of fatty acids with aUcycHc structures. These are of great biological importance and are formed by i vivo oxidation of 20-carbon polyunsaturated fatty acids, particularly arachidonic acid [27400-91-5]. Several prostaglandins, eg, PGE [745-65-3] have different degrees of unsaturation and oxidation when compared to the parent compound, prostanoic acid [25151 -18-9]. 

Lipoxygenase-Catalyzed Oxidations. Lipoxygenase-1 catalyzes the incorporation of dioxygen into polyunsaturated fatty acids possessing a l(Z),4(Z)-pentadienyi moiety to yield ( ),(Z)-conjugated hydroperoxides. A highly active preparation of the enzyme from soybean is commercially available in purified form. From a practical standpoint it is important to mention that the substrate does not need to be in solution to undergo the oxidation. Indeed, the treatment of 28 g/L of linoleic acid [60-33-3] with 2 mg of the enzyme results in (135)-hydroperoxide of linoleic acid in 80% yield... 

Prostaglandin biosynthesis from C20 polyunsaturated fatty acids occurs by way of the endoperoxides PGG2 and PGH2. 

Although vegetable oils usually contain a higher proportion of nnsatnrated fatty acids than do animal oils and fats, several plant oils are actually high in saturated fats. Palm oil is low in polyunsaturated fatty acids and particularly high in (saturated) palmitic acid (whence the name palmitic). Coconut oil is particularly high in lanric and myristic acids (both saturated) and contains very few nnsatnrated fatty acids. 

Degradation of Polyunsaturated Fatty Acids Requires 2,4-Dienoyl-CoA Reductase... 

Polyunsaturated fatty acids pose a slightly more complicated situation for the cell. Consider, for example, the case of linoleic acid shown in Figure 24.24. As with oleic acid, /3-oxidation proceeds through three cycles, and enoyl-CoA isomerase converts the cA-A double bond to a trans-b double bond to permit one more round of /3-oxidation. What results this time, however, is a cA-A enoyl-CoA, which is converted normally by acyl-CoA dehydrogenase to a trans-b, cis-b species. This, however, is a poor substrate for the enoyl-CoA hydratase. This problem is solved by 2,4-dienoyl-CoA reductase, the product of which depends on the organism. The mammalian form of this enzyme produces a trans-b enoyl product, as shown in Figure 24.24, which can be converted by an enoyl-CoA isomerase to the trans-b enoyl-CoA, which can then proceed normally through the /3-oxidation pathway. Escherichia coli possesses a... 

FIGURE 24.24 The oxidation pathway for polyunsaturated fatty adds, illustrated for linoleic add. Three cycles of /3-oxidation on linoleoyl-CoA yield the cis-A, d.s-A intermediate, which is converted to a tran.s-A, cis-A intermediate. An additional round of /S-oxi-dation gives d.s-A enoyl-CoA, which is oxidized to the trans-A, d.s-A species by acyl-CoA dehydrogenase. The subsequent action of 2,4-dienoyl-CoA reductase yields the trans-A product, which is converted by enoyl-CoA isomerase to the tran.s-A form. Normal /S-oxida-tion then produces five molecules of acetyl-CoA. 

Organisms differ with respect to formation, processing, and utilization of polyunsaturated fatty acids. E. coli, for example, does not have any polyunsaturated fatty acids. Eukaryotes do synthesize a variety of polyunsaturated fatty acids, certain organisms more than others. For example, plants manufacture double bonds between the A and the methyl end of the chain, but mammals cannot. Plants readily desaturate oleic acid at the 12-position (to give linoleic acid) or at both the 12- and 15-positions (producing linolenic acid). Mammals require polyunsaturated fatty acids, but must acquire them in their diet. As such, they are referred to as essential fatty acids. On the other hand, mammals can introduce double bonds between the double bond at the 8- or 9-posi-tion and the carboxyl group. Enzyme complexes in the endoplasmic reticulum desaturate the 5-position, provided a double bond exists at the 8-position, and form a double bond at the 6-position if one already exists at the 9-position. Thus, oleate can be unsaturated at the 6,7-position to give an 18 2 d5-A ,A fatty acid. 

Animal cells can modify arachidonic acid and other polyunsaturated fatty acids, in processes often involving cyclization and oxygenation, to produce so-called local hormones that (1) exert their effects at very low concentrations and (2) usually act near their sites of synthesis. These substances include the prostaglandins (PG) (Figure 25.27) as well as thromboxanes (Tx), leukotrienes, and other hydroxyeicosanoic acids. Thromboxanes, discovered in blood platelets (thrombocytes), are cyclic ethers (TxBg is actually a hemiacetal see Figure 25.27) with a hydroxyl group at C-15. 

More than LOO different fatty acids are known, and about 40 occur widely. Palmitic acid (C ) and stearic acid (Cjy) are the most abundant saturated fatty adds oleic and linoleic acids (both Care the most abundant unsaturated ones. Oleic acid is monounsaturated since it has only one double bond, whereas linoleic, linolenic, and arachidonic acids are polyunsaturated fatty acids because they have more than one double bond. Linoleic and linolenic... 

CH3CH2CH=CHCH2CH=CHCH2CH=CHCH2CH2CH2CH2CH2CH2CH2COH Linolenic acid, a polyunsaturated fatty acid... 

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