Long-chain n-3 PUFA

Samieri C, Lorrain S, Buaud B, Vaysse C, Berr C, Peuchant E et al (2013) Relationship between diet and plasma long-chain n-3 PUFAs in older people Impact of apolipo-protein E genotype. J Lipid Res 54 2559-2567... 

Sijben, J. W. and Calder, P. C. Differential immunomodulation with long-chain n-3 PUFA in health and chronic disease. Proc Nutr Soc 66 (2007) 237-259. 

FA distribution in TAG as well as in phospholipids affects the physical properties, lipolitic and oxidative stability, and nutritional availability of lipids. In many TAG, the FA are arranged in a nonrandom distribution. In plants, monoenoic FA and PUFA are dominant at a sn-2 position (Orthoefer, 1996). In pig depot fat and in cow s milk, the TAG sn-2 position is occupied by palmitic acid. The distribution is also different in cattle and sheep depot fats (Love, 1996). In blubber seals, long-chain n-3 PUFA are esterified rather in sn-l,3 positions, whereas, in muscle, TAG in the sn-2 position that is typical for the lipid muscles of nearly all fish (Ackman, 1994). Enzymatic syntheses of structured TAG containing dY-5,8,ll,14,17-eicosapentaenoic acid (EPA) and dY-4,7,10,13,16,19-docosahexaenoic acid (DHA) in the sn-2 position with medium-chain FA at the end positions are particularly interesting (Halldorsson... 

Newton, I.S., 1996, Food enrichment with long-chain n-3 PUFA, Inform, 7(2), 169. 

The serum phospholipids and red cell membrane phospholipids of children with SCD have an altered fatty acid composition. We and others (2123) have shown that children with SCD have lower percentages of the long-chain n-3 PUFA and increased percentages of saturated fatty acids in their phospholipids. In addition, Connor and co-workers (22) documented that the red cell membrane phospholipids of children with SCD have a higher proportion of saturated and monounsaturated fatty acids and a lower proportion of PUFA in the sn-2 position. This abnormality in fatty acid content can be reversed by supplementation with PUFA, as demonstrated by Muskeit and co-workers (23) who found an increase in the level of n-3 fatty acids in both plasma cholesterol esters and red blood cell phospholipids of children with SCD after supplementation with fish oil. 

Bauch A, Lindtner O, Mensink GBM, Niemann B (2006) Dietary intake and sources of long-chain n-3 PUFAs in German adults. European Journal of Nutrition 60 810-812. 

As the number of double bonds increases in polyunsaturated fatty acids (PUFA), they produce more complex mixtures of hydroperoxides, which are easily decomposed and become very difficult to analyse quantitatively. The most important long-chain n-3 PUFA found in fish, marine and algae oils include all cw-5,8,ll,14,17-eicosapentaenoic acid (EPA), and all ds-4,7,10,13,16,19-docosahexaenoic acid (DHA). The hydroperoxides produced from EPA and DHA have been identified but not quantified. By the same mechanism established for linolenate, EPA produced the eight 5-, 8-, 9-, 11-, 12-, 14-, 15- and 18-hydroperoxides. DHA produced the ten 4-, 7-, 8-, 10-, 11-, 13-, 14-, 16-, 17-and 20-hydroperoxides. 

The large number of precursors of volatile decomposition products affecting the flavor of oils has been discussed in Chapter 4. Only qualitative information is available on the relative oxidative stability of hydroperoxides, aldehydes and secondary oxidation products. As observed with the unsaturated fatty ester precursors, the stability of hydroperoxides and unsaturated aldehydes decreases with higher unsaturation. Different hydroperoxides of unsaturated lipids, acting as precursors of volatile flavor compounds, decompose at different temperatures. Hydroperoxides of linolenate and long-chain n-3 PUFA decompose more readily and at lower temperatures than hydroperoxides of linoleate and oleate. Similarly, the alkadienals are less stable than alkenals, which in turn are less stable than alkanals. The short-chain fatty acids produced by oxidation of unsaturated aldehydes will further decrease the oxidative stability of polyunsaturated oils. For secondary products, dimers are less stable than dihydroperoxides, which are less stable than cyclic peroxides. 

These methods measure the amount of oxygen absorbed during lipid oxidation. Because they measure a reactant and not a product of oxidation, they are of limited sensitivity and require high levels of oxidation as end-point for induction periods and are unsuitable for detecting subtle effects of long-chain n-3 PUFA producing fishy odors. The information provided is therefore not closely related to flavor stability. 

To support this hypothesis, Enser et al. (50) showed that both whole linseed and fish oil supplements elevated CLA deposition from 5.7 to 8.0 mg/100 g beef muscle. The elevation in CLA was from two- to threefold greater compared with a ration containing more saturated fat (3.2 mg/100 g muscle) (50). The long-chain n-3 PUFA in the fish oil supplement offered to beef cattle was more potent than linseed oil in increasing the CLA deposition in muscle hpid because linseed oil had a greater total amount of n-3 fatty acids (55% 18 3n-3) than the fish oil (33% 20 5n-3 and 22 6n-3). 

These observations suggest that changing the fatty acid composition of cell membranes may alter the function of membrane proteins and so may affect cell functions. Increased dietary intake of fatty acids normally consumed in low amounts (e.g. long-chain n-3 PUFA) results in the incorporation of these fatty acids into cell membranes, and this might be one mechanism by which dietary fats affect cell function, physiological responses and health. 

Further information on the health benefits of long-chain n-3 PUFA can be found in the British Nutrition Foundation (1992, 1999), Nettleton (1995), Kremer (1998), Simopoulos (1998), and Hamazaki and Okuyama (2001). 

Fish oils are the main source of EPA, DHA and some other long-chain n-3 PUFA (see also Chapter 8). They generally contain approximately 50 different fatty acids. The most prominent are listed in Table 11 for a range of common fish oils. 

ALA, an essential fatty acid present as a relatively high proportion of the total fatty acids in some vegetable oils such as perilla and chia (60-70%), flaxseed (55-60%), canola (-10%), soybean (-7%), and walnut (-13%) oils, is the precursor of and long-chain n-3 polyunsaturated fatty acids (PUFA). DHA and EPA are the predominant long-chain n-3 PUFA found in fish, fish oils, and other marine organisms. DPA is a major long-chain n-3 PUFA found in fish, meat, and meat products. 

Reasons proposed for the relatively poor conversion efficiency of ALA to EPA and DHA are that a substantial proportion of the ALA is diverted to P-oxidation (discussed above), that ALA is found distributed throughout all major tissue lipid pools (adipose, carcass, skin), and that in animals ALA might be excreted onto the fur (as discussed above). In addition, LA is the major dietary PUFA and is a competitive inhibitor of the metabolism of ALA to 18 4n-3 (commonly known as stearidonic acid see Chapter 9), a precursor of long-chain n-3 PUFA (see Figure 1). Furthermore, diets rich in LA decrease expression of the hepatic A -desaturase compared with fat-free diets this presumably also reduces the possibility of conversion of ALA to 18 4n-3 and of 24 5n-3 to 24 6n-3 (Cho et al, 1999a). 

A major rate-limiting step in the conversion of ALA to EPA and other long-chain n-3 PUFA is considered to be the first A -desaturation. This is demonstrated effectively by consideration of data from studies involving feeding 18 4n-3, the product of the A -desaturation of ALA, to humans or animals. In one study, a group of 32 stroke patients supplemented their diets with one of three diets for 3 weeks (1) a mixture of 7.5% blackcurrant seed oil [rich in 18 4n-3 and y-linolenic acid (GLA 18 3n-6)], 50% soybean oil, and 42.5% medium-chain... 

The effect of long-chain n-3 PUFA from fish on blood pressure has been evaluated in a meta-analysis of 31 placebo-controlled trials in 1356 subjects. The results indicated that in a group of studies on people with hypertension, average systolic blood pressures fell by 3.4 mm Hg and diastolic blood... 

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