Triglyceride
Types of fats in food |
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Components |
Manufactured fats |
A triglyceride (TG, triacylglycerol, TAG, or triacylglyceride) is an
Triglycerides are the main constituents ofMany types of triglycerides exist. One specific classification focuses on saturated and unsaturated types. Saturated fats have no C=C groups; unsaturated fats feature one or more C=C groups. Unsaturated fats tend to have a lower melting point than saturated analogues; as a result, they are often liquid at room temperature.
Chemical structure
The three fatty acids
Most natural fats contain a complex mixture of individual triglycerides. Because of their heterogeneity, they melt over a broad range of temperatures. Cocoa butter is unusual in that it is composed of only a few triglycerides, derived from palmitic, oleic, and stearic acids in the 1-, 2-, and 3-positions of glycerol, respectively.[4]
The simplest triglycerides are those where the three fatty acids are identical. Their names indicate the fatty acid:
A triglyceride containing different fatty acids is known as a mixed triglyceride.[6] These are more common in nature.
If the first and third fatty acids on the glycerol differ, then the mixed triglyceride is chiral.[7]
Physical properties
Triglycerides are colorless, although degraded samples can appear yellowish. Stearin, a simple, saturated, symmetrical triglyceride, is a solid near room temperature, but most examples are oils. Their density is near 0.-0.9 g/cm3.
Biosynthesis
Triglycerides are tri-esters derived from the condensation reaction of glycerol with three fatty acids. Their formation can be summarised by the following overall equation:
- CH(OH)(CH2OH)2 + RCOOH + R'COOH + R"COOH → RC(O)OCH2−CH(OC(O)R')−CH2C(O)OR" + 3H2O
In nature, the formation of triglycerides is not random; rather, specific fatty acids are selectively condensed with the hydroxyl functional groups of glycerol. Animal fats typically have unsaturated fatty acid residues on carbon atoms 1 and 3. Extreme examples of non-random fats are
- CH(OH)(CH2OH)2 + H2PO−4 → HOCH2−CH(OH)−CH2−OPO3H− + H2O
The three oxygen atoms in this phosphate ester are differentiated, setting the stage for regiospecific formation of triglycerides, as the diol reacts selectively with coenzyme-A derivatives of the fatty acids, RC(O)S–CoA:
- HOCH2−CH(OH)−CH2−OPO3H− + RC(O)S−CoA + R'C(O)S−CoA → RC(O)O−CH2−CH(−OC(O)R')−CH2−OPO3H− + 2HS−CoA
The phosphate ester linkage is then hydrolysed to make way for the introduction of a third fatty acid ester:
- RC(O)O−CH2−CH(−OC(O)R')−CH2−OPO3H− + H2O → RC(O)O−CH2−CH(−OC(O)R')−CH2OH + H2PO−4
- RC(O)O−CH2−CH(−OC(O)R')−CH2OH + R"C(O)S−CoA → RC(O)O−CH2−CH(−OC(O)R')−CH2−OC(O)R" + HS−CoA
Nomenclature
Common fat names
Fats are usually named after their source (like olive oil, cod liver oil, shea butter, tail fat) or have traditional names of their own (like butter, lard, ghee, and margarine). Some of these names refer to products that contain substantial amounts of other components besides fats proper.
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.
IUPAC
In the
- 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 "(9Z)" - 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((9Z)-octadec-9-enoate) 3-(hexadecanoate) applies to the pheromone informally named as glyceryl 1,2-dioleate-3-palmitate,[8] and also known by other common names including 1,2-dioleoyl-3-palmitoylglycerol, glycerol dioleate palmitate, and 3-palmito-1,2-diolein.
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, (9E,11E,13Z)-octadeca-9,11,13-trienoic acid according to IUPAC nomenclature, has the code "18:3 cis-13 trans-9,11".
Saturated and unsaturated fats
For human nutrition, an important classification of fats is based on the number and position of
Unsaturated fatty acids are further classified into
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) | |
α-Linolenic acid (polyunsaturated, C18:3 cis-9,12,15, omega-3)
| |
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
.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
The double bonds in unsaturated fats can be converted into single bonds by reaction with hydrogen effected by a catalyst. This process, called
In cellular
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 (rancidity). Antioxidants can protect unsaturated fat from lipid peroxidation.
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 molecules attacking the carbon backbone.
Triglycerides are also split into their components via
Staining
Interactive pathway map
Click on genes, proteins and metabolites below to link to respective articles. [§ 1]
- ^ The interactive pathway map can be edited at WikiPathways: "Statin_Pathway_WP430".
See also
- Diglyceride acyltransferase, an enzyme that produces triglycerides
- Glycerol-3-phosphate acyltransferases, enzymes involved in early step in biosynthesis of triglycerides
- Phosphatidic acids, playing a role in biosynthesis of triglycerides
- Medium-chain triglycerides
- Lipid profile
- Lipids
- Vertical auto profile
- Hypertriglyceridemia, the presence of high amounts of triglycerides in the blood.
References
- ^ "Nomenclature of Lipids". IUPAC-IUB Commission on Biochemical Nomenclature (CBN). Retrieved 2007-03-08.
- ^
Nelson, D. L.; Cox, M. M. (2000). Lehninger, Principles of Biochemistry (3rd ed.). New York: Worth Publishing. ISBN 1-57259-153-6.
- ^
Lampe, M. A.; Burlingame, A. L.; Whitney, J.; Williams, M. L.; Brown, B. E.; Roitman, E.; Elias, M. (1983). "Human stratum corneum lipids: characterization and regional variations". J. Lipid Res. 24 (2): 120–130. PMID 6833889.
- ^ a b c d e
Alfred Thomas (2002). "Fats and Fatty Oils". ISBN 3527306730.
- ^
Charbonnet, G. H.; Singleton, W. S. (1947). "Thermal properties of fats and oils". S2CID 101805872.
- ^ "Mixed triglyceride | chemical compound | Britannica". www.britannica.com. Retrieved 2023-02-13.
- ^
Lok, C.M.; Ward, J.P.; van Dorp, D.A. (1976). "The synthesis of Chiral Glycerides starting from D- and L-serine". Chemistry and Physics of Lipids. 16 (2): 115–122. PMID 1269065.
- ^
- OCLC 865143943.
- ^ a b "Essential Fatty Acids". Micronutrient Information Center, Oregon State University, Corvallis, OR. May 2014. Retrieved 24 May 2017.
- ^ a b "Omega-3 fatty acids, fish oil, alpha-linolenic acid". Mayo Clinic. 2017. Retrieved 24 May 2017.
- ^ Institute of Shortenings and Edible oils (2006). "Food Fats and oils" (PDF). Archived from the original (PDF) on 2007-03-26. Retrieved 2009-02-19.
- PMID 21731420.
- S2CID 84433984.
External links
- Lowering Triglycerides (EMedicineHealth.com; October 2020)