Polyunsaturated acids

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 ... 

FIGURE 3-7 Pathways for the interconversion of brain fatty acids. Palmitic acid (16 0) is the main end product of brain fatty acid synthesis. It may then be elongated, desaturated, and/or P-oxidized to form different long chain fatty acids. The monoenes (18 1 A7, 18 1 A9, 24 1 A15) are the main unsaturated fatty acids formed de novo by A9 desaturation and chain elongation. As shown, the very long chain fatty acids are a-oxidized to form a-hydroxy and odd numbered fatty acids. The polyunsaturated fatty acids are formed mainly from exogenous dietary fatty acids, such as linoleic (18 2, n-6) and a-linoleic (18 2, n-3) acids by chain elongation and desaturation at A5 and A6, as shown. A A4 desaturase has also been proposed, but its existence has been questioned. Instead, it has been shown that unsaturation at the A4 position is effected by retroconversion i.e. A6 unsaturation in the endoplasmic reticulum, followed by one cycle of P-oxidation (-C2) in peroxisomes [11], This is illustrated in the biosynthesis of DHA (22 6, n-3) above. In severe essential fatty acid deficiency, the abnormal polyenes, such as 20 3, n-9 are also synthesized de novo to substitute for the normal polyunsaturated acids. 

The incorporation of the polyunsaturated fatty acid in position two depends upon removal of the monounsatu-rated fatty acid and replacement by the polyunsaturated acid. This is achieved by the action of two enzymes, (i) a deacylase and (ii) an acyltransferase. 

These processes are shown for the CoA ester of linoleic acid, the most common of the polyunsaturated acids. 

Because they are necessary precursors for the synthesis of other products, linoleate and linolenate are essential fatty acids for mammals they must be obtained from dietary plant material. Once ingested, linoleate may be converted to certain other polyunsaturated acids, particularly y-linolenate, eicosatrienoate, and arachidonate (eicosatetraenoate), all of which can... 

Because of animal biohydrogenation, the content of polyunsaturated acids in milk is low, currently reported at about 5% (Smith et al 1978), and is associated mostly with the phospholipids. While quantitatively unimportant, these acids are the most susceptible targets of oxidation and provide the essential fatty acids (EFA), mostly cis, cis-9, 12-18 2. 

In addition to the major fatty acids, milk also contains many minor polyunsaturated acids (Kurtz 1974) hence the autoxidation of dairy products can lead to a multitude of saturated and unsaturated aldehydes. 

Recent interest has focused on the C20 5 eicosa-pentaenoic acid (EPA) and the C22 6 docosa-hexaenoic acids (DHA). These 3 (or n-3) polyunsaturated acids are formed from linolenic acid by marine algae and are found in fish oils.h The C22 5 and C22 6 acids can be converted to prostaglandins of the PG4 and PG5 series. DHA together with the 0)6 C22 4 acid constitutes over 30% of the fatty acids in brain phospholipids. In the... 

If the analysis of fatty acid methyl esters gives a large amount of information on the composition of fats, there remain some unsolved problems, related to the two major flaws of the approach. The transesterification of TGs derived from polyunsatured acids is not always quantitative. A more important and general problem is that the method does not provide any information regarding the actual composition of the TGs. 

Cooper and Anders (20) reported the HPLC analysis of unsaturated C l8 and C20 fatty acids. Since the methylene-interrupted polyunsaturated acids show no specific UV absorption, the 2-naphtacylesters were prepared for UV detection at 254 nm [the column was a 3-ft X 0.07-in.-lD stainless steel tube packed withCORASIL-Ci8, methanol/water(85 15) served as the eluent, and a flow rate of 12 ml/h was obtained at a pressure of 300 psig]. The lower detection limit was 4-90 ng of ester. 

On the other hand, some fish are able to synthesize long-chain polyenoic fatty acids (Kayama et al., 1963) from shorter carbon chains. Docosohexaenoic acid is laid down in coho salmon in quantities related to the size of the fish, rather than to its availability in the diet (Tinsley et al., 1973). Rainbow trout fed on 18 2 and 18 3 fatty acids can produce 20 3, 22 5 and 22 6 fatty acids in substantial quantities (Owen et al., 1975), but these workers noticed that the capacity of marine flatfish to elongate or desaturate the carbon chains was more limited. They found that 70% of the radioactivity of labelled 18 3 appeared later in the 22 6 fatty acid of rainbow trout, but that turbot converted only 3-15% of labelled precursors into polyunsaturated fatty acids of longer chain length. It was suggested that turbot in the wild probably received adequate polyunsaturated acids in their diet, which the fish therefore did not need to modify. The elongation of the carbon chains and the creation of more double bonds is also only slight in Atlantic cod, another marine teleost, presumably for the same reason (Ross, 1977). 

The UV method is based on measurements of extinction or optical density in the 232 nm and 270 nm regions in which diene and triene conjugated systems are known to absorb UV. The intensity of the UV spectral absorption band at 232 nm and 270 nm is also useful to detect, and also in part to quantify, both the extent of the oxidation of monounsaturated and polyunsaturated acid moieties... 

Lipids As the capacity of the stomach of newborns is very limited, lipids and fat are necessary to provide the large amounts of energy required by the newborn s high body growth rate. Milk fat is the major source of lipid that mammalian newborns use for accumulating body adipose tissue and for the development of their nervous system. The major lipids in milk fat are triglycerides, which represent more than 98 percent of the neutral lipids. From a quantitative point of view, there is no difference in the fat content in cow s (3.8 percent) and human milk (3.7 percent), but they do differ in their qualitative composition in fact, in cow s milk the predominant fatty acids are saturated acids, while polyunsaturated acids are the main fatty acids in human milk, as shown in Table 13.3. 

Salem, N., Kim, H.Y., Lyergey, J.A. (1986). Docosahexaenoic acid membrane fimction and metabolism. In Health Ejfects of Polyunsaturated Acids in Seafoods (R.E. Martin, ed.), pp. 263-317. Academic Press, New York. 

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