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A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an
ester An ester is a derived from an (organic or inorganic) in which at least one –OH group is replaced by an –O– () group, as in the substitution reaction of a and an . s are s of ; they are important in biology, being one of the main classe ...

ester
derived from
glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
and three
fatty acids In chemistry Chemistry is the scientific Science () is a systematic enterprise that builds and organizes knowledge Knowledge is a familiarity or awareness, of someone or something, such as facts A fact is an occurrence in ...
(from ''
tri- Numeral or number prefixes are prefix A prefix is an which is placed before the of a word. Adding it to the beginning of one word changes it into another word. For example, when the prefix ''un-'' is added to the word ''happy'', it creates ...
'' and ''
glyceride , the simplest possible fat after Triformin Glycerides, more correctly known as acylglycerols, are esters formed from glycerol and fatty acids, and are generally very hydrophobic. Glycerol has three hydroxyl functional groups, which can be este ...
''). Triglycerides are the main constituents of
body fat Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the four basic types of animal tissue (biology), tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesod ...
in humans and other vertebrates, as well as
vegetable fat Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of fats from seeds ...
. They are also present in the blood to enable the bidirectional transference of
adipose Adipose tissue, body fat, or simply fat is a loose connective tissue Connective tissue is one of the four basic types of animal tissue (biology), tissue, along with epithelial tissue, muscle tissue, and nervous tissue. It develops from the mesod ...

adipose
fat and blood glucose from the liver, and are a major component of
human skin oils
human skin oils
. Many types of triglycerides exist. One specific classification focuses on
saturated and unsaturated In chemistry, a saturated compound is a chemical compound (or ion) that resists the addition reactions, such as hydrogenation, oxidative addition, and binding of a Lewis base. The term is used in many contexts and for many classes of chemical com ...
types.
Saturated fat A saturated fat is a type of fat In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any indivi ...
s have ''no'' C=C groups;
unsaturated fat In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies ...
s feature one or more C=C groups. Unsaturated fats tend to have a lower
melting point The melting point (or, rarely, liquefaction point) of a substance is the temperature Temperature ( ) is a physical quantity that expresses hot and cold. It is the manifestation of thermal energy Thermal radiation in visible light can b ...

melting point
than saturated analogues; as a result, they are often
liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned with the motions of physical objects, ...

liquid
at room temperature.


Chemical structure

Triglycerides are tri-esters consisting of a
glycerol Glycerol (; also called glycerine in British English and glycerin in American English) is a simple polyol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
bound to three
fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo during ...
molecules.
Alcohols In chemistry, alcohol is an organic compound that carries at least one hydroxyl functional group (−OH) bound to a Saturated and unsaturated compounds, saturated carbon atom. The term alcohol originally referred to the primary alcohol ethan ...

Alcohols
have a hydroxyl (HO–) group. Organic acids have a carboxyl (–COOH) group. Alcohols and organic acids join to form
esters An ester is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held together by chemical ...

esters
. The glycerol molecule has three hydroxyl (HO–) groups and each fatty acid has a
carboxyl A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...
group (–COOH). In triglycerides, the hydroxyl groups of the glycerol join the carboxyl groups of the fatty acid to form
ester An ester is a derived from an (organic or inorganic) in which at least one –OH group is replaced by an –O– () group, as in the substitution reaction of a and an . s are s of ; they are important in biology, being one of the main classe ...

ester
bonds: :HOCH2CH(OH)CH2OH + RCO2H + R′CO2H + R″CO2H → RCO2CH2CH(O2CR′)CH2CO2R″ + 3H2O The three fatty acids (RCO2H, R′CO2H, R″CO2H in the above equation) are usually different, as many kinds of triglycerides are known. The chain lengths of the fatty acids in naturally occurring triglycerides vary, but most contain 16, 18, or 20
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
atoms. Natural fatty acids found in plants and animals are typically composed of only even numbers of carbon atoms, reflecting the pathway for their biosynthesis from the two-carbon building-block
acetyl CoA Acetyl-CoA (acetyl coenzyme A) is a molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life i ...

acetyl CoA
. Bacteria, however, possess the ability to synthesise odd- and branched-chain fatty acids. As a result,
ruminant Ruminants ( Ruminantia) are large herbivorous grazing or browsing s that are able to acquire nutrients from plant-based food by it in a specialized prior to digestion, principally through microbial actions. The process, which takes place in th ...
animal fat contains odd-numbered fatty acids, such as 15, due to the action of
bacteria Bacteria (; common noun bacteria, singular bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typ ...

bacteria
in the
rumen The rumen, also known as a paunch, is the largest stomach compartment in ruminants and the larger part of the reticulorumen, which is the first chamber in the alimentary canal of ruminant animals. The rumen's microbial favoring environment allows ...
. Many fatty acids are unsaturated; some are polyunsaturated (e.g., those derived from
linoleic acid Linoleic acid is an organic compound , CH4; is among the simplest organic compounds. In chemistry Chemistry is the scientific discipline involved with Chemical element, elements and chemical compound, compounds composed of atoms, molecules ...

linoleic acid
). Most natural fats contain a complex mixture of individual triglycerides. Because of this, they melt over a broad range of temperatures. Cocoa butter is unusual in that it is composed of only a few triglycerides, derived from , , and acids in the 1-, 2-, and 3-positions of glycerol, respectively.


Homo- and heterotriglycerides

The simplest triglycerides are those where the three fatty acids are identical. Their names indicate the fatty acid:
stearin Stearin , or tristearin, or glyceryl tristearate is an odourless, white powder. It is a triglyceride derived from three units of stearic acid. Most triglycerides are derived from at least two and more commonly three different fatty acid fatty a ...

stearin
derived from
stearic acid Stearic acid ( , ) is a saturated fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry Chemistry is the scientific discipline involved ...

stearic acid
,
palmitin Tripalmitin is a triglyceride derived from the fatty acid palmitic acid. References

Triglycerides Palmitate esters {{ester-stub ...
derived from
palmitic acid Palmitic acid, or hexadecanoic acid in IUPAC nomenclature The International Union of Pure and Applied Chemistry The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations t ...

palmitic acid
, etc. These compounds can be obtained in three crystalline forms ( polymorphs): α, β, and β′, the three forms differing in their melting points. If the first and third fatty acids on the glycerol differ, then the triglyceride is
chiral Chirality is a property of important in several branches of science. The word ''chirality'' is derived from the (''kheir''), "hand", a familiar chiral object. An object or a system is ''chiral'' if it is distinguishable from its ; that is, i ...
.


Conformation

The shape of fat and fatty acid molecules is usually not well-defined. Any two parts of a molecule that are connected by just one single bond are free to rotate about that bond. Thus a fatty acid molecule with ''n'' simple bonds can be deformed in ''n''-1 independent ways (counting also rotation of the terminal
methyl group A methyl group is an alkyl derived from methane, containing one carbon atom chemical bond, bonded to three hydrogen atoms — CH3. In chemical formula, formulas, the group is often skeletal formula#Pseudoelement symbols, abbreviated ...

methyl group
). Such rotation cannot happen across a double bond, except by breaking and then reforming it with one of the halves of the molecule rotated by 180 degrees, which requires crossing a significant
energy barrier provide the activation energy to initiate combustion in this Bunsen burner. The blue flame sustains itself after the sparks stop because the continued combustion of the flame is now energetically favorable. In chemistry and physics, activation ene ...
. Thus a fat or fatty acid molecule with double bonds (excluding at the very end of the chain) can have multiple cis–trans isomers with significantly different chemical and biological properties. Each double bond reduces the number of conformational
degrees of freedom Degrees of Freedom (often abbreviated df or DOF) refers to the number of independent variables or parameters of a system. In various scientific fields, the word "freedom" is used to describe the limits to which physical movement or other physical ...
by one. Each triple bond forces the four nearest carbons to lie in a straight line, removing two degrees of freedom. It follows that depictions of "saturated" fatty acids with no double bonds (like stearic) having a "straight zig-zag" shape, and those with one ''cis'' bond (like oleic) being bent in an "elbow" shape are somewhat misleading. While the latter are a little less flexible, both can be twisted to assume similar straight or elbow shapes. In fact, outside of some specific contexts like crystals or bilayer membranes, both are more likely to be found in randomly contorted configurations than in either of those two shapes.


Examples

Stearic acid is a saturated fatty acid (with only single bonds) found in animal fats, and is the intended product in full hydrogenation. Oleic acid has a double bond (thus being "unsaturated") with ''cis'' geometry about midway in the chain; it makes up 55–80% of olive oil. Elaidic acid is its ''trans'' isomer; it may be present in partially hydrogenated vegetable oils, and also occurs in the fat of the
durian The durian () is the edible fruit of several tree species In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biolog ...

durian
fruit (about 2%) and in milk fat (less than 0.1%). Vaccenic acid is another ''trans'' acid that differs from elaidic only in the position of the double bond; it also occurs in milk fat (about 1-2%).


Nomenclature


Common fat names

Fats are usually named after their source (like
olive oil Olive oil is a liquid fat obtained from olive The olive, botanical name ''Olea europaea'', meaning "European olive", is a species In biology, a species is the basic unit of biological classification, classification and a taxonomi ...

olive oil
,
cod liver oil Cod liver oil is a dietary supplement A dietary supplement is a manufactured product intended to supplement one's diet by taking a pill, capsule, tablet, powder or liquid. A supplement can provide nutrients either extracted from foo ...

cod liver oil
,
shea butter Shea butter (, , or ) is a fat extracted from the nut of the African shea tree (''Vitellaria paradoxa''). It is ivory in color when raw and commonly dyed yellow with borututu root or palm oil. It is widely used in cosmetics as a moisturizer, sa ...

shea butter
,
tail fat Tail fat is the fat of some breeds of sheep Sheep (''Ovis aries'') are quadrupedal, ruminant mammals typically kept as livestock. Like all ruminants, sheep are members of the order(biology), order Artiodactyla, the even-toed ungulates. Although ...
) or have traditional names of their own (like butter, lard,
ghee Ghee () is a class of clarified butter Clarified butter is milk fat rendered from butter to separate the milk solids and water from the butterfat. Typically, it is produced by melting butter and allowing the components to separate by densi ...

ghee
, and
margarine Margarine (, also , ) is a spread used for flavoring, baking and cooking. It is most often used as a substitute for butter. Although originally made from animal fats, most margarine consumed today is made from vegetable oil. The foodstuff was or ...

margarine
). Some of these names refer to products that contain substantial amounts of other components besides fats proper.


Chemical fatty acid names

In chemistry and biochemistry, dozens of saturated fatty acids and of hundreds of unsaturated ones have traditional scientific/technical names usually inspired by their source fats (butyric, , stearic, oleic, , and ), but sometimes their discoverer (
mead Mead () is an Alcoholic drink, alcoholic beverage created by Ethanol fermentation, fermenting honey with water, sometimes with various fruits, spices, grains, or hops. The alcoholic content ranges from about 3.5% Alcohol by volume, ABV to more ...

mead
, ). A triglyceride would then be named as an ester of those acids, such as "glyceryl 1,2-dioleate 3-palmitate".N. Koeniger and H. J. Veith (1983): "Glyceryl-1,2-dioleate-3-palmitate, a brood pheromone of the honey bee (''Apis mellifera'' L.)". ''Experientia'', volume 39, pages 1051–1052


IUPAC

In the general chemical nomenclature developed by the
International Union of Pure and Applied Chemistry The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Science Council (ISC). IUPAC ...
(IUPAC), the recommended name of a fatty acid, derived from the name of the corresponding
hydrocarbon In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, prop ...
, completely describes its structure, by specifying the number of carbons and the number and position of the double bonds. Thus, for example, oleic acid would be called "(9Z)-octadec-9-enoic acid", meaning that it has an 18 carbon chain ("octadec") with a carboxyl at one end ("oic") and a double bound at carbon 9 counting from the carboxyl ("9-en"), and that the configuration of the single bonds adjacent to that double bond is ''cis'' ("(9Z)") The IUPAC nomenclature can also handle branched chains and derivatives where hydrogen atoms are replaced by other chemical groups. A triglyceride would then be named according to general ester rules as, for example, "propane-1,2,3-tryl 1,2-bis((9Z)-octadec-9-enoate) 3-(hexadecanoate)".


Fatty acid code

A notation specific for fatty acids with unbranched chain, that is as precise as the IUPAC one but easier to parse, is a code of the form ": cis- trans-", where is the number of carbons (including the carboxyl one), is the number of double bonds, is a list of the positions of the ''cis'' double bonds, and is a list of the positions of the ''trans'' bounds. Either list and the label is omitted if there are no bounds of that type. Thus, for example, the codes for stearic, oleic, elaidic, and vaccenic acids would be "18:0", "18:1 cis-9", "18:1 trans-9", and "18:1 trans-11", respectively. The code for α-oleostearic acid, which is "(9E,11E,13Z)-octadeca-9,11,13-trienoic acid" in the IUPAC nomenclature, has the code "18:3 trans-9,11 cis-13"


Classification


By chain length

Fats can be classified according to the lengths of the carbon chains of their constituent fatty acids. Most chemical properties, such as melting point and acidity, vary gradually with this parameter, so there is no sharp division. Chemically,
formic acid Formic acid, systematically named methanoic acid, is the simplest carboxylic acid A carboxylic acid is an organic acid An organic acid is an organic compound with acidic properties. The most common organic acids are the carboxylic acid ...

formic acid
(1 carbon) and
acetic acid Acetic acid , systematically named ethanoic acid , is a colourless liquid organic compound with the chemical formula CH3COOH (also written as CH3CO2H, C2H4O2, or HC2H3O2). Vinegar is no less than 4% acetic acid by volume, making acetic acid ...

acetic acid
(2 carbons) could be viewed as the shortest fatty acids; then would be the simplest triglyceride. However, the terms "fatty acid" and "fat" are usually reserved for compounds with substantially longer chains. A division commonly made in biochemistry and nutrition is: * Short-chain fatty acid (SCFA) with less than six carbons (e. g.
butyric acid Butyric acid (from grc, βούτῡρον, meaning "butter"), also known under the systematic name butanoic acid, is a straight-chain alkyl In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study o ...

butyric acid
). * Medium-chain fatty acid (MCFA) with 6 to 12 carbons (e.g.
capric acid Capric acid, also known as decanoic acid or decylic acid, is a saturated fatty acid A saturated fat is a type of fat in which the fatty acid chains have all or predominantly single bond In chemistry Chemistry is the scientific discipl ...
). * Long-chain fatty acids (LCFA) with 13 to 21 carbons (e.g.
petroselinic acid Petroselinic acid is a fatty acid that occurs naturally in several animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Hete ...

petroselinic acid
). * Very long chain fatty acids (VLCFA) with 22 or more carbons (e. g.
cerotic acid Cerotic acid, or hexacosanoic acid, is a 26-carbon Carbon (from la, carbo "coal") is a chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an ...

cerotic acid
with 26) A triglyceride molecule may have fatty acid elements of different lengths, and a fat product will often be a mix of various triglycerides. Most fats found in food, whether vegetable or animal, are made up of medium to long-chain fatty acids, usually of equal or nearly equal length.


Saturated and unsaturated fats

For human nutrition, an important classification of fats is based on the number and position of
double bond In chemistry, a double bond is a covalent bond A covalent bond is a chemical bond A chemical bond is a lasting attraction between atom An atom is the smallest unit of ordinary matter In classical physics and general chemistry, ...

double bond
s in the constituent fatty acids. Saturated fat has a predominance of
saturated fatty acid A saturated fat is a type of fat In nutrition Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and ...
s, without any double bonds, while unsaturated fat has predominantly unsaturated acids with double bonds. (The names refer to the fact that each double bond means two fewer hydrogen atoms in the chemical formula. Thus, a saturated fatty acid, having no double bonds, has the maximum number of hydrogen atoms for a given number of carbon atoms — that is, it is "saturated" with hydrogen atoms.) Unsaturated fatty acids are further classified into
monounsaturated In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any individual contiguous system that embodies ...
(MUFAs), with a single double bond, and
polyunsaturated In nutrition Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and biology, biochemistry may be divided ...
(PUFAs), with two or more. Natural fats usually contain several different saturated and unsaturated acids, even on the same molecule. For example, in most vegetable oils, the saturated (C16:0) and (C18:0) are usually attached to positions 1 and 3 (sn1 and sn3) of the glycerol hub, whereas the middle position (sn2) is usually occupied by an unsaturated one, such as (C18:1, ω–9) or (C18:2, ω–6).) While it is the ''nutritional'' aspects of polyunsaturated fatty acids that are generally of greatest interest, these materials also have non-food applications. They include the
drying oils A drying oil is an oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All ev ...
, such as linseed (flax seed), tung,
poppy seed Poppy seed is an oilseed Vegetable oils, or vegetable fats, are oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance that ...
,
perilla ''Perilla'' is a genus consisting of one major Asiatic crop species ''Perilla frutescens ''Perilla frutescens'', commonly called perilla or Korean perilla, is a species of '' Perilla'' in the mint family Lamiaceae. It is an annual plant nativ ...
, and
walnut oil Walnut oil is oil An oil is any nonpolar In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to ...
, which
polymerize In polymer chemistry, polymerization (American English American English (AmE, AE, AmEng, USEng, en-US), sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United State ...
on exposure to
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
to form solid films, and are used to make
paints Paint is any pigmented liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned wi ...

paints
and
varnishes Varnish is a clear transparent Transparency, transparence or transparent most often refer to transparency and translucency, the physical property of allowing the transmission of light through a material. They may also refer to: Literal use ...
. Saturated fats generally have a higher melting point than unsaturated ones with the same molecular weight, and thus are more likely to be solid at room temperature. For example, the animal fats
tallow Tallow is a rendering (industrial), rendered form of beef or mutton fat, primarily made up of triglycerides. In industry, tallow is not strictly defined as beef or mutton fat. In this context, tallow is animal fat that conforms to certain techni ...

tallow
and
lard Lard is a semi-solid white fat In nutrition Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. A sub-discipline of both chemistry and ...
are high in saturated fatty acid content and are solids. Olive and linseed oils on the other hand are unsaturated and liquid. Unsaturated fats are prone to
oxidation Redox (reduction–oxidation, pronunciation: or ) is a type of chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter ...

oxidation
by air, which causes them to become rancid and inedible. The double bonds in unsaturated fats can be converted into single bonds by reaction with hydrogen effected by a catalyst. This process, called
hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, m ...
, is used to turn vegetable oils into solid or semisolid
vegetable fat Vegetable oils, or vegetable fats, are oils extracted from seeds or from other parts of fruits. Like animal fats, vegetable fats are ''mixtures'' of triglycerides. Soybean oil, grape seed oil, and cocoa butter are examples of fats from seeds ...
s like
margarine Margarine (, also , ) is a spread used for flavoring, baking and cooking. It is most often used as a substitute for butter. Although originally made from animal fats, most margarine consumed today is made from vegetable oil. The foodstuff was or ...

margarine
, which can substitute for tallow and butter and (unlike unsaturated fats) can be stored indefinitely without becoming rancid. However, partial hydrogenation also creates some unwanted ''trans'' acids from ''cis'' acids. In cellular
metabolism Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life Life is a characteristic that distinguishes physical entities A bubble of exhaled gas in water In common usage and classical mechanics, a phys ...

metabolism
, unsaturated fat molecules yield slightly less energy (i.e., fewer
calories The calorie is a unit of energy Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a ...
) than an equivalent amount of saturated fat. The heats of combustion of saturated, mono-, di-, and tri-unsaturated 18-carbon fatty acid esters have been measured as 2859, 2828, 2794, and 2750 kcal/mol, respectively; or, on a weight basis, 10.75, 10.71, 10.66, and 10.58 kcal/g — a decrease of about 0.6% for each additional double bond. The greater the degree of unsaturation in a fatty acid (i.e., the more double bonds in the fatty acid) the more vulnerable it is to
lipid peroxidation Lipid peroxidation is the chain of reactions of oxidative (mild reducing agent) are added to powdered potassium permanganate Potassium permanganate is an inorganic compound with the chemical formula KMnO4 and composed of potassium ion, K+ and ...

lipid peroxidation
( rancidity).
Antioxidant Antioxidants are compounds Compound may refer to: Architecture and built environments * Compound (enclosure), a cluster of buildings having a shared purpose, usually inside a fence or wall ** Compound (fortification), a version of the above ...

Antioxidant
s can protect unsaturated fat from lipid peroxidation.


Cis and trans fats

Another important classification of unsaturated fatty acids considers the ''cis''–''trans'' isomerism, the spatial arrangement of the C–C
single bond In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and the changes they undergo duri ...

single bond
s adjacent to the double bonds. Most unsaturated fatty acids that occur in nature have those bonds in the ''cis'' ("same side") configuration. Partial
hydrogenation Hydrogenation is a chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substance A chemical substance is a form of matter In classical physics and general chemistry, m ...

hydrogenation
of ''cis'' fats can turn some of their fatty acids into ''trans'' ("opposite sides") variety.
Elaidic acid Elaidic acid is a chemical compound with the formula , specifically the fatty acid with structural formula HO(O=)C–(CH2–)7CH=CH–(CH2–)8H, with the double bond (between carbon atoms 9 and 10) in cis-trans isomerism, ''trans'' configuration. ...

Elaidic acid
is the ''trans'' isomer of oleic acid, one of the most common fatty acids in human diet. The single change of configuration in one double bond causes them to have different chemical and physical properties. Elaidic acid has a much higher melting point than oleic acid, 45 instead of 13.4 °C. This difference is commonly attributed to the supposed ability of the trans molecules to pack more tightly, forming a solid that is more difficult to break apart.


Omega number

Another classification considers the position of the double bonds relative to the ''end'' of the chain (opposite to the
carboxyl group A carboxylic acid is an organic acid that contains a carboxyl group (C(=O)OH) attached to an R-group. The general formula of a carboxylic acid is R−COOH or R−CO2H, with substituent, R referring to the alkyl, alkenyl, aryl, or other group. ...

carboxyl group
). The position is denoted by "ω−''k''" or "n−''k''", meaning that there is a double bond between carbons ''k'' and ''k''+1 counted from 1 at that end. For example,
alpha-Linolenic acid α-Linolenic acid (ALA), (from Greek Greek may refer to: Greece Anything of, from, or related to Greece Greece ( el, Ελλάδα, , ), officially the Hellenic Republic, is a country located in Southeast Europe. Its population is approxi ...

alpha-Linolenic acid
is a "ω−3" or "n−3" acid, meaning that there is a double bond between the third and fourth carbons, counted from that end; that is, its
structural formula The structural formula of a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) composed of atoms from more than one chemical element, element held toge ...
ends with –CH=CH––.Karen Dooley (2008):
Omega-three fatty acids and diabetes
. Online article at th
University of Florida's UFHealt
website. Accessed on 2020-08-30.


Examples of saturated fatty acids

Some common examples of fatty acids: *
Butyric acid Butyric acid (from grc, βούτῡρον, meaning "butter"), also known under the systematic name butanoic acid, is a straight-chain alkyl In organic chemistry Organic chemistry is a branch of chemistry Chemistry is the study o ...

Butyric acid
with 4 carbon atoms (contained in
butter Butter is a dairy product Dairy products or milk products are a type of food Food is any substance consumed to provide Nutrient, nutritional support for an organism. Food is usually of plant, animal or Fungus, fungal origin, and contai ...

butter
) *
Lauric acid Lauric acid or systematically, dodecanoic acid, is a saturated fatty acid A saturated fat is a type of fat in which the fatty acid chains have all or predominantly single bond In chemistry Chemistry is the scientific discipline involve ...

Lauric acid
with 12 carbon atoms (contained in
coconut oil Coconut oil (or coconut butter) is an edible oil derived from the wick, meat, and milk of the coconut palm The coconut tree (''Cocos nucifera'') is a member of the palm tree The Arecaceae is a family (biology), family of Perennial pla ...

coconut oil
,
palm kernel oil Palm kernel oil is an edible plant oil Plant oils or vegetable oils are oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substance th ...
, and
breast milk Breast milk or mother's milk is milk Milk is a nutrient A nutrient is a substance used by an organism to survive, grow, and reproduce. The requirement for dietary nutrient intake applies to animal Animals (also called Metazoa) are ...
) *
Myristic acid Myristic acid (IUPAC The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering OrganizationsNational Adhering Organizations in chemistry are the organizations that work as the authorita ...

Myristic acid
with 14 carbon atoms (contained in cow's
milk Milk is a nutrient A nutrient is a substance Substance may refer to: * Substance (Jainism), a term in Jain ontology to denote the base or owner of attributes * Chemical substance, a material with a definite chemical composition * Matter, any ...

milk
and dairy products) *
Palmitic acid Palmitic acid, or hexadecanoic acid in IUPAC nomenclature The International Union of Pure and Applied Chemistry The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations t ...

Palmitic acid
with 16 carbon atoms (contained in
palm oil Palm oil is an edible vegetable oil Vegetable oils, or vegetable fats, are oil An oil is any nonpolar chemical substance A chemical substance is a form of matter In classical physics and general chemistry, matter is any substa ...

palm oil
and
meat Meat is animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiratio ...

meat
) *
Stearic acid Stearic acid ( , ) is a saturated fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properti ...

Stearic acid
with 18 carbon atoms (also contained in
meat Meat is animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiratio ...

meat
and
cocoa butter Cocoa butter, also called theobroma oil, is a pale-yellow, edible fat In nutrition Nutrition is the biochemical Biochemistry or biological chemistry, is the study of chemical processes within and relating to living organisms. ...
)


Examples of unsaturated fatty acids

* C14:1, ω−5, ''cis''-9-tetradecenoic acid * C16:1 ω−10, ''cis''-6-Hexadecenoic acid *
Palmitoleic acid Palmitoleic acid, or (9''Z'')-hexadec-9-enoic acid, is an omega-7 monounsaturated In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀ ...

Palmitoleic acid
C16:1, ω−7 , ''cis''-9-hexadecenoic acid *
Oleic acid Oleic acid is a fatty acid In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, behavior and t ...

Oleic acid
C18:1 ω−9, ''cis''-9-octadecenoic acid *
Petroselinic acid Petroselinic acid is a fatty acid that occurs naturally in several animal Animals (also called Metazoa) are multicellular eukaryotic organisms that form the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Hete ...

Petroselinic acid
C18:1 ω−12, ''cis''-Octadec-6-enoic acid * ''cis''-Vaccenic acid, C18:1 ω−7), ''cis''-11-octadecenoic acid *
Vaccenic acid Vaccenic acid is a naturally occurring trans fatty acid. It is the predominant kind of trans-fatty acid found in human milk, in the fat of ruminant Ruminants are herbivorous mammals of the suborder Ruminantia that are able to acquire nutrients f ...

Vaccenic acid
C18:1 ω−7, ''trans''-11-octadecenoic acid *
Elaidic acid Elaidic acid is a chemical compound with the formula , specifically the fatty acid with structural formula HO(O=)C–(CH2–)7CH=CH–(CH2–)8H, with the double bond (between carbon atoms 9 and 10) in cis-trans isomerism, ''trans'' configuration. ...

Elaidic acid
18:1 ω−9, ''trans''-9-octadecenoic acid (''trans''-oleic acid) *
Linoleic acid Linoleic acid is an organic compound In chemistry Chemistry is the study of the properties and behavior of . It is a that covers the that make up matter to the composed of s, s and s: their composition, structure, properties, beha ...

Linoleic acid
*
Linolenic acid Linolenic acid is a type of fatty acid fatty acids have perfectly straight chain structure. Unsaturated ones are typically bent, unless they have a trans configuration. In chemistry Chemistry is the scientific discipline involved with Ch ...
* C20:1 ω−7, ''cis''-13-eicosenoic acid *
Gadoleic acid Gadoleic acid (20:1 n−11) is an unsaturated fatty acid In nutrition Nutrition is the biochemical and physiological process by which an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organi ...

Gadoleic acid
C20:1 ω−11, ''cis''-9-icosenoic acid * 11-Eicosenoic acid, Gondoic acid 20:1 ω−9, ''cis''-11-eicosenoic acid * Erucic acid C22:1 ω−9, ''cis''-15-tetracosenoic acid * Brassidic acid C22:1 ω−9, ''trans''-15-tetracosenoic acid * Nervonic acid C24:1 ω−9, , ''cis''-15-tetracosenoic acid * Arachidonic acid


Industrial uses

Linseed oil and related oils are important components of useful products used in oil paints and related coatings. Linseed oil is rich in di- and tri-unsaturated fatty acid components, which tend to harden in the presence of oxygen. This heat-producing hardening process is peculiar to these so-called ''drying oils''. It is caused by a polymerization process that begins with
oxygen Oxygen is the chemical element Image:Simple Periodic Table Chart-blocks.svg, 400px, Periodic table, The periodic table of the chemical elements In chemistry, an element is a pure substance consisting only of atoms that all have the same ...

oxygen
molecules attacking the
carbon Carbon (from la, carbo "coal") is a with the C and 6. It is lic and —making four s available to form s. It belongs to group 14 of the periodic table. Carbon makes up only about 0.025 percent of Earth's crust. Three occur naturally, ...

carbon
backbone. Triglycerides are also split into their components via transesterification during the manufacture of biodiesel. The resulting fatty acid
ester An ester is a derived from an (organic or inorganic) in which at least one –OH group is replaced by an –O– () group, as in the substitution reaction of a and an . s are s of ; they are important in biology, being one of the main classe ...

ester
s can be used as fuel in diesel engines. The glycerin has many uses, such as in the manufacture of food and in the production of pharmaceuticals.


Staining

Staining (biology), Staining for fatty acids, triglycerides, lipoproteins, and other lipids is done through the use of lysochromes (fat-soluble dyes). These dyes can allow the qualification of a certain fat of interest by staining the material a specific color. Some examples: Sudan IV, Oil Red O, and Sudan Black B.


Interactive pathway map


See also

* Diglyceride acyltransferase, enzyme responsible for triglyceride biosynthesis * Medium-chain triglycerides * Lipid profile * Lipids * Vertical auto profile


References

{{Authority control Triglycerides, Lipid disorders Esters