Polyunsaturated fatty acid

(Redirected from Polyunsaturated)

Polyunsaturated fatty acids (PUFAs) are fatty acids that contain more than one double bond in their backbone. This class includes many important compounds, such as essential fatty acids and those that give drying oils their characteristic property.

Polyunsaturated fats are fats in which the constituent hydrocarbon chain possesses two or more carbon–carbon double bonds.[1][2] Polyunsaturated fat can be found mostly in nuts, seeds, fish, seed oils, and oysters.[1] "Unsaturated" refers to the fact that the molecules contain less than the maximum amount of hydrogen (if there were no double bonds). These materials exist as cis or trans isomers depending on the geometry of the double bond.

Chemical structureEdit

Saturated fats have hydrocarbon chains which can be most readily aligned. The hydrocarbon chains in trans fats align more readily than those in cis fats, but less well than those in saturated fats. In general, this means that the melting points of fats increase from cis to trans unsaturated and then to saturated. See the section about the chemical structure of fats for more information.

 
Chemical structure of the polyunsaturated fat linoleic acid.
 
3D representation of linoleic acid in a bent conformation.
 
Chemical structure of alpha-linolenic acid (ALA), an essential omega−3 fatty acid.

The position of the carbon-carbon double bonds in carboxylic acid chains in fats is designated by Greek letters.[1] The carbon atom closest to the carboxyl group is the alpha carbon, the next carbon is the beta carbon and so on. In fatty acids the carbon atom of the methyl group at the end of the hydrocarbon chain is called the omega carbon because omega is the last letter of the Greek alphabet. Omega-3 fatty acids have a double bond three carbons away from the methyl carbon, whereas omega-6 fatty acids have a double bond six carbons away from the methyl carbon. The illustration below shows the omega-6 fatty acid, linoleic acid.

While it is the nutritional aspects of polyunsaturated fats that are generally of greatest interest, these materials also have non-food applications. Drying oils, which polymerize on exposure to oxygen to form solid films, are polyunsaturated fats. The most common ones are linseed (flax seed) oil, tung oil, poppy seed oil, perilla oil, and walnut oil. These oils are used to make paints and varnishes.

Polyunsaturated fatty acids can be classified in various groups by their chemical structure:

Based on the length of their carbon backbone, they are sometimes classified in two groups:[3]

  • short chain polyunsaturated fatty acids (SC-PUFA), with 18 carbon atoms
  • long-chain polyunsaturated fatty acids (LC-PUFA) with 20 or more carbon atoms

Dietary sourcesEdit

Properties of vegetable oils[4][5]
The nutritional values are expressed as percent (%) by mass of total fat.
Type Processing
treatment[6]
Saturated
fatty acids
Monounsaturated
fatty acids
Polyunsaturated
fatty acids
Smoke point
Total[4] Oleic
acid
(ω-9)
Total[4] α-Linolenic
acid
(ω-3)
Linoleic
acid
(ω-6)
ω-6:3
ratio
Avocado[7] 11.6 70.6 52–66[8] 13.5 1 12.5 12.5:1 250 °C (482 °F)[9]
Brazil nut[10] 24.8 32.7 31.3 42.0 0.1 41.9 419:1 208 °C (406 °F)[11]
Canola[12] 7.4 63.3 61.8 28.1 9.1 18.6 2:1 204 °C (400 °F)[13]
Coconut[14] 82.5 6.3 6 1.7 175 °C (347 °F)[11]
Corn[15] 12.9 27.6 27.3 54.7 1 58 58:1 232 °C (450 °F)[13]
Cottonseed[16] 25.9 17.8 19 51.9 1 54 54:1 216 °C (420 °F)[13]
Cottonseed[17] hydrogenated 93.6 1.5 0.6 0.2 0.3 1.5:1
Flaxseed/linseed[18] 9.0 18.4 18 67.8 53 13 0.2:1 107 °C (225 °F)
Grape seed   10.5 14.3 14.3   74.7 74.7 very high 216 °C (421 °F)[19]
Hemp seed[20] 7.0 9.0 9.0 82.0 22.0 54.0 2.5:1 166 °C (330 °F)[21]
High-oleic safflower oil[22] 7.5 75.2 75.2 12.8 0 12.8 very high 212 °C (414 °F)[11]
Olive, Extra Virgin[23] 13.8 73.0 71.3 10.5 0.7 9.8 14:1 193 °C (380 °F)[11]
Palm[24] 49.3 37.0 40 9.3 0.2 9.1 45.5:1 235 °C (455 °F)
Palm[25] hydrogenated 88.2 5.7 0
Peanut[26] 16.2 57.1 55.4 19.9 0.318 19.6 61.6:1 232 °C (450 °F)[13]
Rice bran oil 25 38.4 38.4 36.6 2.2 34.4[27] 15.6:1 232 °C (450 °F)[28]
Sesame[29] 14.2 39.7 39.3 41.7 0.3 41.3 138:1
Soybean[30] 15.6 22.8 22.6 57.7 7 51 7.3:1 238 °C (460 °F)[13]
Soybean[31] partially hydrogenated 14.9 43.0 42.5 37.6 2.6 34.9 13.4:1
Sunflower[32] 8.99 63.4 62.9 20.7 0.16 20.5 128:1 227 °C (440 °F)[13]
Walnut oil[33] unrefined 9.1 22.8 22.2 63.3 10.4 52.9 5:1 160 °C (320 °F)[34]
Food Saturated Mono-
unsaturated
Poly-
unsaturated
As weight percent (%) of total fat
Cooking oils
Algal oil[35] 4 92 4
Canola[36] 8 64 28
Coconut oil 87 13 0
Corn oil 13 24 59
Cottonseed oil[36] 27 19 54
Olive oil[37] 14 73 11
Palm kernel oil[36] 86 12 2
Palm oil[36] 51 39 10
Peanut oil[38] 17 46 32
Rice bran oil 25 38 37
Safflower oil, high oleic[39] 6 75 14
Safflower oil, linoleic[36][40] 6 14 75
Soybean oil 15 24 58
Sunflower oil[41] 11 20 69
Mustard oil 11 59 21
Dairy products
Butterfat[36] 66 30 4
Cheese, regular 64 29 3
Cheese, light 60 30 0
Ice cream, gourmet 62 29 4
Ice cream, light 62 29 4
Milk, whole 62 28 4
Milk, 2% 62 30 0
Whipping cream[42]* 66 26 5
Meats
Beef 33 38 5
Ground sirloin 38 44 4
Pork chop 35 44 8
Ham 35 49 16
Chicken breast 29 34 21
Chicken 34 23 30
Turkey breast 30 20 30
Turkey drumstick 32 22 30
Fish, orange roughy 23 15 46
Salmon 28 33 28
Hot dog, beef 42 48 5
Hot dog, turkey 28 40 22
Burger, fast food 36 44 6
Cheeseburger, fast food 43 40 7
Breaded chicken sandwich 20 39 32
Grilled chicken sandwich 26 42 20
Sausage, Polish 37 46 11
Sausage, turkey 28 40 22
Pizza, sausage 41 32 20
Pizza, cheese 60 28 5
Nuts
Almonds dry roasted 9 65 21
Cashews dry roasted 20 59 17
Macadamia dry roasted 15 79 2
Peanut dry roasted 14 50 31
Pecans dry roasted 8 62 25
Flaxseeds, ground 8 23 65
Sesame seeds 14 38 44
Soybeans 14 22 57
Sunflower seeds 11 19 66
Walnuts dry roasted 9 23 63
Sweets and baked goods
Candy, chocolate bar 59 33 3
Candy, fruit chews 14 44 38
Cookie, oatmeal raisin 22 47 27
Cookie, chocolate chip 35 42 18
Cake, yellow 60 25 10
Pastry, Danish 50 31 14
Fats added during cooking or at the table
Butter, stick 63 29 3
Butter, whipped 62 29 4
Margarine, stick 18 39 39
Margarine, tub 16 33 49
Margarine, light tub 19 46 33
Lard 39 45 11
Shortening 25 45 26
Chicken fat 30 45 21
Beef fat 41 43 3
Goose fat[43] 33 55 11
Dressing, blue cheese 16 54 25
Dressing, light Italian 14 24 58
Other
Egg yolk fat[44] 36 44 16
Avocado[45] 16 71 13
Unless else specified in boxes, then reference is:[46]
* 3% is trans fats

TypesEdit

Methylene-interrupted polyenesEdit

These fatty acids have 2 or more cis double bonds that are separated from each other by a single methylene bridge (-CH
2
-). This form is also sometimes called a divinylmethane pattern.[47]

Methylene- interrupted double bonds
−C−C=C−C−C=C−

The essential fatty acids are all omega-3 and -6 methylene-interrupted fatty acids. See more at Essential fatty acids—Nomenclature[48]

Omega-3Edit

Common name Lipid name Chemical name
Omega-3 fatty acids, polyunsaturated
Hexadecatrienoic acid (HTA) 16:3 (n-3) all-cis 7,10,13-hexadecatrienoic acid
Alpha-linolenic acid (ALA) 18:3 (n-3) all-cis-9,12,15-octadecatrienoic acid
Stearidonic acid (SDA) 18:4 (n-3) all-cis-6,9,12,15,-octadecatetraenoic acid
Eicosatrienoic acid (ETE) 20:3 (n-3) all-cis-11,14,17-eicosatrienoic acid
Eicosatetraenoic acid (ETA) 20:4 (n-3) all-cis-8,11,14,17-eicosatetraenoic acid
Eicosapentaenoic acid (EPA, Timnodonic acid) 20:5 (n-3) all-cis-5,8,11,14,17-eicosapentaenoic acid
Heneicosapentaenoic acid (HPA) 21:5 (n-3) all-cis-6,9,12,15,18-heneicosapentaenoic acid
Docosapentaenoic acid (DPA, Clupanodonic acid) 22:5 (n-3) all-cis-7,10,13,16,19-docosapentaenoic acid
Docosahexaenoic acid (DHA, Cervonic acid) 22:6 (n-3) all-cis-4,7,10,13,16,19-docosahexaenoic acid
Tetracosapentaenoic acid 24:5 (n-3) all-cis-9,12,15,18,21-tetracosapentaenoic acid
Tetracosahexaenoic acid (Nisinic acid) 24:6 (n-3) all-cis-6,9,12,15,18,21-tetracosahexaenoic acid

Omega-6Edit

Common name Lipid name Chemical name
Omega-6 fatty acids, polyunsaturated
Linoleic acid (LA) 18:2 (n-6) all-cis-9,12-octadecadienoic acid
Gamma-linolenic acid (GLA) 18:3 (n-6) all-cis-6,9,12-octadecatrienoic acid
Eicosadienoic acid 20:2 (n-6) all-cis-11,14-eicosadienoic acid
Dihomo-gamma-linolenic acid (DGLA) 20:3 (n-6) all-cis-8,11,14-eicosatrienoic acid
Arachidonic acid (AA) 20:4 (n-6) all-cis-5,8,11,14-eicosatetraenoic acid
Docosadienoic acid 22:2 (n-6) all-cis-13,16-docosadienoic acid
Adrenic acid (AdA) 22:4 (n-6) all-cis-7,10,13,16-docosatetraenoic acid
Docosapentaenoic acid (DPA) 22:5 (n-6) all-cis-4,7,10,13,16-docosapentaenoic acid
Tetracosatetraenoic acid 24:4 (n-6) all-cis-9,12,15,18-tetracosatetraenoic acid
Tetracosapentaenoic acid 24:5 (n-6) all-cis-6,9,12,15,18-tetracosapentaenoic acid

Omega-9Edit

Common name Lipid name Chemical name
Omega-9 fatty acids, mono- and polyunsaturated
Oleic acid 18:1 (n-9) cis-9-octadecenoic acid
Eicosenoic acid 20:1 (n-9) cis-11-eicosenoic acid
Mead acid 20:3 (n-9) all-cis-5,8,11-eicosatrienoic acid
Erucic acid 22:1 (n-9) cis-13-docosenoic acid
Nervonic acid 24:1 (n-9) cis-15-tetracosenoic acid
Monounsaturated

Conjugated fatty acidsEdit

Conjugated double bonds
-C=C-C=C-
Common name Lipid name Chemical name
Conjugated fatty acids  have two or more conjugated double bonds
Conjugated Linoleic Acids (two conjugated double bonds)
Rumenic acid 18:2 (n-7) 9Z,11E-octadeca-9,11-dienoic acid
  18:2 (n-6) 10E,12Z-octadeca-10,12-dienoic acid
Conjugated Linolenic Acids (three conjugated double bonds)
α-Calendic acid 18:3 (n-6) 8E,10E,12Z-octadecatrienoic acid
β-Calendic acid 18:3 (n-6) 8E,10E,12E-octadecatrienoic acid
Jacaric acid 18:3 (n-6) 8Z,10E,12Z-octadecatrienoic acid
α-Eleostearic acid 18:3 (n-5) 9Z,11E,13E-octadeca-9,11,13-trienoic acid
β-Eleostearic acid 18:3 (n-5) 9E,11E,13E-octadeca-9,11,13-trienoic acid
Catalpic acid 18:3 (n-5) 9Z,11Z,13E-octadeca-9,11,13-trienoic acid
Punicic acid 18:3 (n-5) 9Z,11E,13Z-octadeca-9,11,13-trienoic acid
Other
Rumelenic acid 18:3 (n-3) 9E,11Z,15E-octadeca-9,11,15-trienoic acid
α-Parinaric acid 18:4 (n-3) 9E,11Z,13Z,15E-octadeca-9,11,13,15-tetraenoic acid
β-Parinaric acid 18:4 (n-3) all trans-octadeca-9,11,13,15-tetraenoic acid
Bosseopentaenoic acid 20:5 (n-6) 5Z,8Z,10E,12E,14Z-eicosapentaenoic acid

Other polyunsaturated fatty acidsEdit

Common name Lipid name Chemical name
Pinolenic acid 18:3 (n-6) (5Z,9Z,12Z)-octadeca-5,9,12-trienoic acid
Sciadonic acid 20:3 (n-6) (5Z,11Z,14Z)-eicosa-5,11,14-trienoic acid

Function and effectsEdit

The biological effects of the ω-3 and ω-6 fatty acids are largely mediated by their mutual interactions, see Essential fatty acid interactions for detail.

HealthEdit

Potential benefitsEdit

Because of their effects in the diet, unsaturated fats (monounsaturated and polyunsaturated) are often referred to as good fats; while saturated fats are sometimes referred to as bad fats. Some fat is needed in the diet, but it is usually considered that fats should not be consumed excessively, unsaturated fats should be preferred, and saturated fats in particular should be limited.[49][50][51][52]

In preliminary research, omega-3 fatty acids in algal oil, fish oil, fish and seafood have been shown to lower the risk of heart attacks.[53] Other preliminary research indicates that omega-6 fatty acids in sunflower oil and safflower oil may also reduce the risk of cardiovascular disease.[54]

Among omega-3 fatty acids, neither long-chain nor short-chain forms were consistently associated with breast cancer risk. High levels of docosahexaenoic acid (DHA), however, the most abundant omega-3 polyunsaturated fatty acid in erythrocyte (red blood cell) membranes, were associated with a reduced risk of breast cancer.[55] The DHA obtained through the consumption of polyunsaturated fatty acids is positively associated with cognitive and behavioral performance.[56] In addition DHA is vital for the grey matter structure of the human brain, as well as retinal stimulation and neurotransmission.[1]

Contrary to conventional advice, an evaluation of evidence from 1966-1973 pertaining to the health impacts of replacing dietary saturated fat with linoleic acid found that participants in the group doing so had increased rates of death from all causes, coronary heart disease, and cardiovascular disease.[57] Although this evaluation was disputed by many scientists,[58] it fueled debate over worldwide dietary advice to substitute polyunsaturated fats for saturated fats.[59]

PregnancyEdit

Polyunsaturated fat supplementation does not decrease the incidence of pregnancy-related disorders, such as hypertension or preeclampsia, but may increase the length of gestation slightly and decreased the incidence of early premature births.[1]

Expert panels in the United States and Europe recommend that pregnant and lactating women consume higher amounts of polyunsaturated fats than the general population to enhance the DHA status of the fetus and newborn.[1]

CancerEdit

Results from observational clinical trials on polyunsaturated fat intake and cancer have been inconsistent and vary by numerous factors of cancer incidence, including gender and genetic risk.[53] Some studies have shown associations between higher intakes and/or blood levels of polyunsaturated fat omega-3s and a decreased risk of certain cancers, including breast and colorectal cancer, while other studies found no associations with cancer risk.[53][60]

Thermal degradationEdit

Polyunsaturated fatty acids in culinary oils undergo oxidative deterioration at temperatures of 150 °C (302 °F). The heating causes a free radical chain reaction, which oxidizes the PUFAs into hydroperoxide, which further decomposes into a complex mixture of secondary products.[61]

See alsoEdit

ReferencesEdit

CitationsEdit

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General ReferencesEdit