The number of theoretically possible molecular species increases with the growing number of fatty acids forming a mixture of TAGs, see Table 1. When the two primary hydroxyl groups are esterified with different fatty acids, the resulting triacylglycerol can be asymmetric and thus can display "optical activity", although this is usually too low to be measured. compounds having the same FA and the same molecular weight, it is surprising that a mere change in the positions of two FA on the glycerol backbone shifts the melting point by as much as 10 ☌.Ī special nomenclature is used for the stereochemistry of TAGs instead of the usual D/L or R/S nomenclature, where the primary hydroxyl groups are often termed α- and α' and the secondary β, or the "stereospecific numbering" ( sn) system recommended by the IUPAC-IUB commission. Although this holds for two regioisomers, i.e. for SLO and SOL, wherein S - stearic, O - oleic, and L - linoleic acid, in which the melting points for individual crystalline α and β forms are -2 to -4 ☌ and -15 to -17 ☌, and -11.5 to -13 ☌ and -18 to -19 ☌, respectively. Despite this, some data have been gathered, e.g. Regretfully, data on the melting points of crystalline forms of TAG regioisomers, as well as enantiomers, are available for only a few of them. One of the possibilities how to achieve this is to keep oil bodies in a fluid - non-crystalline state, which could be achieved by transitions between the crystalline forms. The life functions of the cell have to be retained throughout this temperature range. Most natural fats contain a complex mixture of different TAGs and therefore melt in a wide temperature range. Therefore, ruminant fat also contains acids with an odd number of carbon atoms, for example 15 or 17, because they are produced by bacteria in the rumen. Bacteria, however, have the ability to synthesize acids with odd chain lengths and branched chains. Natural fatty acids in plants and animals are typically composed of only even-numbered chain lengths because they are biosynthesized from acetyl-CoA. The length of the fatty acid chains in naturally occurring TAG may vary, but the most common are chains having 16, 18, 20, or 22 carbon atoms. The three fatty acids RCOOH, R'COOH and R"COOH may be completely different, or two of them or all of them may be identical. ![]() The chemical formula of TAG is RCOO-CH 2-CH(-OOCR')CH 2OOCR" wherein R, R', and R" are long alkyl chains. TAG are formed by one molecule of glycerol esterified by fatty acid molecules in all three OH groups. Triacylglycerols (TAGs) are chemical compounds that are major components of vegetable oils and animal fats. Institute of Microbiology, Prague, Czech Republic Home Lipid Analysis Lipidomics ![]()
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