Triglyceride/ja: Difference between revisions

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===Chemical fatty acid names===

Triglycerides are then commonly named as esters of those acids, as in glyceryl 1,2-dioleate 3-palmitate, the name for a brood pheromone of the honey bee.  Where the fatty acid residues in a triglyceride are all the same, names like [[olein]] (for glyceryl trioleate) and [[palmitin]] (for glyceryl tripalmitate) are common.

In the [[International Union of Pure and Applied Chemistry]]'s (IUPAC's) general [[IUPAC nomenclature of organic chemistry|chemical nomenclature for organic compounds]], any organic structure can be named by starting from its corresponding [[hydrocarbon]] and then specifying differences so as to describe its structure completely. For fatty acids, for example, the position and orientation of carbon-carbon double bonds is specified counting from the [[carboxyl functional group]]. Thus, oleic acid is formally named (9''Z'')-octadec-9-enoic acid, which describes that the compound has:

*an 18 carbon chain ("octadec-") with the carbon of the carboxyl ("-oic acid") given the number 1

*all carbon-carbon bonds are single except for the double bond then joins carbon 9 ("9-en") to carbon 10

*the chain connects to each of the carbons of the double bond on the same side (hence, ''cis'', or "(9''Z'')" - the "''Z''" being an abbreviation for the German word [[zusammen]], meaning together).

IUPAC nomenclature can also handle branched chains and derivatives where hydrogen atoms are replaced by other chemical groups.  Triglycerides take formal IUPAC names according to the rule governing naming of esters.  For example, the formal name propane-1,2,3-tryl 1,2-bis((9''Z'')-octadec-9-enoate) 3-(hexadecanoate) applies to the pheromone informally named as glyceryl 1,2-dioleate-3-palmitate, and also known by other common names including 1,2-dioleoyl-3-palmitoylglycerol, glycerol dioleate palmitate, and 3-palmito-1,2-diolein.

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===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 "{N}:{D} ''cis''-{CCC} ''trans''-{TTT}", where {N} is the number of carbons (including the carboxyl one), {D} is the number of double bonds, {CCC} is a list of the positions of the ''cis'' double bonds, and {TTT} is a list of the positions of the ''trans'' bonds.  Either or both ''cis'' and ''trans'' lists and their labels are omitted if there are no multiple bonds with that geometry.  For example, the codes for stearic, oleic, elaidic, and vaccenic acids are "18:0", "18:1 ''cis''-9", "18:1 ''trans''-9", and "18:1 ''trans''-11", respectively. [[Catalpic acid]], (9''E'',11''E'',13''Z'')-octadeca-9,11,13-trienoic acid according to IUPAC nomenclature, has the code "18:3 ''cis''-13 ''trans''-9,11".

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==Saturated and unsaturated fats==

For human nutrition, an important classification of fats is based on the number and position of [[double bond]]s in the constituent fatty acids.  '''Saturated fat''' has a predominance of [[saturated fatty acid]]s, without any double bonds, while '''unsaturated fat''' has predominantly [[unsaturated fatty acid|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{{snd}}that is, it is "saturated" with hydrogen atoms.)

Unsaturated fatty acids are further classified into '''[[monounsaturated fatty acid|monounsaturated]]''' (MUFAs), with a single double bond, and '''[[polyunsaturated fatty acid|polyunsaturated]]''' (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 [[palmitic acid|palmitic]] (C16:0) and [[stearic acid|stearic]] (C18:0) [[acyl group|acid residues]] 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 [[oleic acid|oleic]] (C18:1, ω–9) or [[linoleic acid|linoleic]] (C18:2, ω–6).)

| [[Stearic acid]] (saturated, C18:0)

| [[Palmitoleic acid]] (mono-unsaturated, C16:1 ''cis''-9,  omega-7)

| [[Oleic acid]] (mono-unsaturated, C18:1 ''cis''-9, omega-9)

| [[alpha-Linolenic acid|α-Linolenic acid]] (polyunsaturated, C18:3 ''cis''-9,12,15, omega-3)

| [[gamma-Linolenic acid|γ-Linolenic acid]] (polyunsaturated, C18:3 ''cis''-6,9,12, omega-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 oil]]s, such as [[linseed oil|linseed (flax seed)]], [[tung oil|tung]], [[poppyseed oil|poppyseed]], [[perilla oil|perilla]], and [[walnut oil]], which [[polymerize]] on exposure to [[oxygen]] to form solid films, and are used to make [[paint]]s and [[varnish]]es.

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]] and [[lard]] 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]] 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 [[fat hydrogenation|hydrogenation]], is used to turn vegetable oils into solid or semisolid [[vegetable fat]]s like [[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]], unsaturated fat molecules yield slightly less energy (i.e., fewer [[calories]]) 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{{snd}}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]] ([[rancidification|rancidity]]). [[Antioxidant]]s can protect unsaturated fat from lipid peroxidation.

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== Industrial uses ==

Linseed oil and related oils are important components of useful products used in [[oil paint]]s 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 molecules attacking the carbon backbone.

Triglycerides are also split into their components via [[transesterification]] during the manufacture of [[biodiesel]]. The resulting fatty acid esters can be used as fuel in [[diesel engine]]s. The [[glycerin]] has many uses, such as in the manufacture of food and in the production of pharmaceuticals.

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== Staining ==

[[Staining (biology)|Staining]] for fatty acids, triglycerides, lipoproteins, and other lipids is done through the use of [[lysochrome]]s (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]].

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== Interactive pathway map ==

{{StatinPathway WP430|highlight=Triglyceride}}