Polyunsaturated fat

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Polyunsaturated fatty acid
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Types of fats in food
Components
Manufactured fats

In biochemistry and nutrition, a polyunsaturated fat is a fat that contains a polyunsaturated fatty acid (abbreviated PUFA), which is a subclass of fatty acid characterized by a backbone with two or more carbon–carbon double bonds.[1][2] Some polyunsaturated fatty acids are essentials. Polyunsaturated fatty acids are precursors to and are derived from polyunsaturated fats, which include drying oils.[3]

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

Nomenclature

The position of the carbon-carbon double bonds in

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
.

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

  • methylene-interrupted polyenes
  • conjugated fatty acids
  • other PUFAs

Based on the length of their carbon backbone, they are sometimes classified in two groups:[4]

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

Production

PUFAs with 18 carbon atoms, which are the most common variety, are not produced by mammals. Since they have important dietary functions, their

dihomo-gamma-linolenic acid.[5]

Industrial PUFAs are generally obtained by hydrolysis of fats that contain PUFAs. The process is complicated by the sensitive nature of PUFAs, leading to side reactions and colorization. Thus, steam hydrolysis often fails for this reason. Alkaline hydrolysis of fats followed by acidification is expensive. Lipases, a family of enzymes, show potential as mild and green catalysts for the production of PUFAs from triglycerides.[3]

In general, PUFAs are undesirable components of vegetable oils, so there is great interest in their removal from, say, olive oil. One technology for lowering the PUFA contact is by selective formation of derivatives with ureas.[3]

Reactions

From the perspective of

iodine numbers
.

PUFAs are highly reactive compared to monounsaturated or saturated analogues. One practical consequence is that polyunsaturated fatty acids have poor shelf life, owing to their tendency toward autoxidation. Metals accelerate the degradation.

Hydrogenation of PUFAs gives less saturated derivatives. For unsaturated products from partial hydrogenation often contain some trans isomers. The trans monounsaturated C20 species elaidic acid can be prepared in this way.[3]

Peroxidation

Main article: Lipid peroxidation

Polyunsaturated fatty acids are susceptible to

allylic C-H bonds. They are drying oils
.

Types

Methylene-interrupted polyenes

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.[6]

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[7]

Omega-3

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
α-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-6

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

Conjugated fatty acids

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 acids

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 effects

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.

Health

Potential benefits

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.[8][9][10][11]

In preliminary research,

safflower oil may also reduce the risk of cardiovascular disease.[13]

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.[14] 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.[15] Although this evaluation was disputed by many scientists,[16] it fueled debate over worldwide dietary advice to substitute polyunsaturated fats for saturated fats.[17]

Taking

deuterated linoleic acid where two atoms of hydrogen substituted with its heavy isotope deuterium, with food (heavy isotope diet) can suppress lipid peroxidation and prevent or treat the associated diseases.[18][19]

Pregnancy

Polyunsaturated fat supplementation does not decrease the incidence of pregnancy-related disorders, such as

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]

Cancer

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.[12] 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.[12][20]

Dietary sources

Properties of vegetable oils[21][22]
The nutritional values are expressed as percent (%) by mass of total fat.
Type Processing
treatment[23]
Saturated

fatty acids
Monounsaturated

fatty acids
Polyunsaturated

fatty acids		 Smoke point
Total[21] Oleic
acid
(ω-9)		 Total[21]
α-Linolenic

acid
(ω-3)		 Linoleic
acid
(ω-6)		 ω-6:3
ratio
Avocado[24] 11.6 70.6 52–66
[25]		 13.5 1 12.5 12.5:1 250 °C (482 °F)[26]
Brazil nut[27] 24.8 32.7 31.3 42.0 0.1 41.9 419:1 208 °C (406 °F)[28]
Canola[29] 7.4 63.3 61.8 28.1 9.1 18.6 2:1 204 °C (400 °F)[30]
Coconut[31] 82.5 6.3 6 1.7 0.019 1.68 88:1 175 °C (347 °F)[28]
Corn[32] 12.9 27.6 27.3 54.7 1 58 58:1 232 °C (450 °F)[30]
Cottonseed[33] 25.9 17.8 19 51.9 1 54 54:1 216 °C (420 °F)[30]
Cottonseed[34]
hydrogenated
 93.6 1.5 0.6 0.2 0.3 1.5:1
Flaxseed/linseed[35] 9.0 18.4 18 67.8 53 13 0.2:1 107 °C (225 °F)
Grape seed   10.4 14.8 14.3   74.9 0.15 74.7 very high 216 °C (421 °F)[36]
Hemp seed[37] 7.0 9.0 9.0 82.0 22.0 54.0 2.5:1 166 °C (330 °F)[38]
High-oleic safflower oil[39]
 7.5 75.2 75.2 12.8 0 12.8 very high 212 °C (414 °F)[28]
Olive, Extra Virgin[40] 13.8 73.0 71.3 10.5 0.7 9.8 14:1 193 °C (380 °F)[28]
Palm[41] 49.3 37.0 40 9.3 0.2 9.1 45.5:1 235 °C (455 °F)
Palm[42] hydrogenated 88.2 5.7 0
Peanut[43] 16.2 57.1 55.4 19.9 0.318 19.6 61.6:1 232 °C (450 °F)[30]
Rice bran oil 25 38.4 38.4 36.6 2.2 34.4[44] 15.6:1 232 °C (450 °F)[45]
Sesame[46] 14.2 39.7 39.3 41.7 0.3 41.3 138:1
Soybean[47] 15.6 22.8 22.6 57.7 7 51 7.3:1 238 °C (460 °F)[30]
Soybean[48]
partially hydrogenated
 14.9 43.0 42.5 37.6 2.6 34.9 13.4:1
Sunflower[49] 8.99 63.4 62.9 20.7 0.16 20.5 128:1 227 °C (440 °F)[30]
Walnut oil[50] unrefined 9.1 22.8 22.2 63.3 10.4 52.9 5:1 160 °C (320 °F)[51]

Polyunsaturated fat can be found mostly in nuts, seeds, fish, seed oils, and

trans isomers
depending on the geometry of the double bond.

Food Saturated Mono-
unsaturated		 Poly-
unsaturated
As weight percent (%) of total fat
Cooking oils
Algal oil[52]
 4 92 4
Canola[53]
 8 64 28
Coconut oil 87 13 0
Corn oil 13 24 59
Cottonseed oil[53] 27 19 54
Olive oil[54] 14 73 11
Palm kernel oil[53] 86 12 2
Palm oil[53] 51 39 10
Peanut oil[55] 17 46 32
Rice bran oil 25 38 37
Safflower oil, high oleic[56] 6 75 14
Safflower oil, linoleic[53][57] 6 14 75
Soybean oil 15 24 58
Sunflower oil[58] 11 20 69
Mustard oil 11 59 21
Dairy products
Butterfat[53] 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[59]* 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[60] 33 55 11
Dressing, blue cheese 16 54 25
Dressing, light Italian 14 24 58
Other
Egg yolk fat[61] 36 44 16
Avocado[62] 16 71 13
Unless else specified in boxes, then reference is:[citation needed]
* 3% is trans fats

Non-dietary applications

PUFA's are significant components of

alkyd resins, which are used in coatings.[3]

See also

References

Citations

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  28. ^
    doi:10.1016/j.foodchem.2009.09.070
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  32. ^ "Corn oil, industrial and retail, all purpose salad or cooking, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  33. ^ "Cottonseed oil, salad or cooking, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  34. ^ "Cottonseed oil, industrial, fully hydrogenated, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  35. ^ "Linseed/Flaxseed oil, cold pressed, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
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  40. ^ "Olive oil, salad or cooking, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  41. ^ "Palm oil, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  42. ^ "Palm oil, industrial, fully hydrogenated, filling fat, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
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  47. ^ "Soybean oil, salad or cooking, fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
  48. ^ "Soybean oil, salad or cooking, (partially hydrogenated), fat composition, 100 g". US National Nutrient Database, Release 28, United States Department of Agriculture. May 2016. Retrieved 6 September 2017.
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  50. ^ "Walnut oil, fat composition, 100 g". US National Nutrient Database, United States Department of Agriculture.
  51. ^ "Smoke Point of Oils". Baseline of Health. Jonbarron.org.
  52. ^ "Thrive Culinary Algae Oil". Retrieved 7 January 2019.
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  54. ^ "NDL/FNIC Food Composition Database Home Page". United States Department of Agriculture, Agricultural Research Service. Retrieved May 21, 2013.
  55. ^ "Basic Report: 04042, Oil, peanut, salad or cooking". USDA. Archived from the original on March 9, 2016. Retrieved 16 January 2015.
  56. ^ "Oil, vegetable safflower, oleic". nutritiondata.com. Condé Nast. Retrieved 10 April 2017.
  57. ^ "Oil, vegetable safflower, linoleic". nutritiondata.com. Condé Nast. Retrieved 10 April 2017.
  58. ^ "Oil, vegetable, sunflower". nutritiondata.com. Condé Nast. Retrieved 27 September 2010.
  59. ^ USDA Basic Report Cream, fluid, heavy whipping
  60. ^ "Nutrition And Health". The Goose Fat Information Service.
  61. ^ "Egg, yolk, raw, fresh". nutritiondata.com. Condé Nast. Retrieved 24 August 2009.
  62. ^ "09038, Avocados, raw, California". National Nutrient Database for Standard Reference, Release 26. United States Department of Agriculture, Agricultural Research Service. Archived from the original on January 10, 2014. Retrieved 14 August 2014.

General References

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