Fatty acids in triacylglycerols

Saturated fatty acids do not contain double bonds in the hydrocarbon chain. Unsaturated fatty acids contain from one to hve double bonds. Those with one double bond are known as monounsaturated, those with two as diunsatu-rated and those with more than two as polyunsaturated fatty acids. A brief summary of the roles of saturated and unsaturated fatty acids is given in Table 11.1. The proportion of these fatty acids in triacylglycerol in human adipose tissue is presented in Table 11.2. 

The abundance of fatty acids in triacylglycerols (TAG) can be determined by conversion of the acyl groups into tertiary alcohols on reaction with an alkyl Grignard reagent, followed by chromatographic separation. The method was found to be of advantage over saponification and conversion to a methyl ester, especially in the determination of short-chain fatty acids, which suffer losses by volatilization. ... 

Certain classes of lipids are susceptible to degradation under specific conditions. For example, all ester-linked fatty acids in triacylglycerols, phospholipids, and sterol esters are released by mild acid or alkaline treatment, and somewhat harsher hydrolysis conditions release amide-bound fatty acids from sphingolipids. Enzymes that specifically hydrolyze certain lipids are also useful in the determination of lipid structure. Phospholipases A, C, and D (Fig. 10-15) each split particular bonds in phospholipids and yield products with characteristic solubilities and chromatographic behaviors. Phospholipase C, for example, releases a water-soluble phosphoryl alcohol (such as phosphocholine from phosphatidylcholine) and a chloroform-soluble diacylglycerol, each of which can be characterized separately to determine the structure of the intact phospholipid. The combination of specific hydrolysis with characterization of the products by thin-layer, gas-liquid, or high-performance liquid chromatography often allows determination of a lipid structure. 

FIGURE 4.14 BC NMR (500 MHz) carbonyl region (173.4-172.0 ppm) of lipids extracted from salmon muscle of four different origins (from top) wild salmon from Norway (NW), Scotland (SW), and Ireland (IW) and farmed salmon from Norway (NF). The position of fatty acids in triacylglycerols is designated (snl,3 or sn2). (From Aursand et al, 2009.)... 

Breakdown The fatty acids in triacylglycerols are released from the glycerol backbone by the action of lipases. The free fatty acids can then be degraded by (3-oxidation to produce energy. The glycerol is converted into dihydroxyacetone phosphate which enters glycolysis. 

Ferrari, R., Esteves, W. and Mukherjee, K. (1997) Alteration of steryl ester content and positional distribution of fatty acids in triacylglycerols by chemical and enzymatic interesterification of plant oils. J. Am. Oil Chem. Soc., 74(2), 93—96. 

Triacylglycerols (Eigure 5.4) consist of a glycerol backbone to which three fatty acids are esterified (Ri.Ra.Rs). Eatty acids are stored as triacylglycerol in all cells, but primarily in adipocytes of adipose tissue. The fatty acids in triacylglycerols are predominantly saturated. The major building block for the synthesis of triacylglycerols, in tissues other than adipose,... 

TABLE 3. Positional Distribution of Fatty Acids in Triacylglycerols of Animal Depot Fats. ... 

Most of the flavor compounds in fats and oils are produced by the reaction of oxygen with unsaturated fatty acids in triacylglycerols or polar lipids. On the other hand, some flavor compounds such as those present in cocoa butter, roasted sesame oil, or roasted peanut oil are generated by the interaction of reducing sugars with amino compounds during thermal processing. 

On the other hand, the specificities of hPL and RmL are very low. RmL strongly favors positions 1 and 3 (rather independent of the type of the fatty acid) in triacylglycerols. To date it is the only lipase that has been crystallized in a complex with an inhibitor containing a short aliphatic chain (Brzozowski et al., 1991). However, the low resolution of the study does not allow for a detailed description of the molecular basis of substrate specificity. Also, no structure-based analysis of stereospecificity in lipases is possible results of purely chemical studies (Kaz-lauskas et al., 1991, and references therein Xie et al., 1990) fall outside the scope of this review. 

Lipoproteins and Lipoprotein Lipase Cellular Uptake and Transport of Fatty Acids Intracellular Consumption of Fatty Acids Fatty Acid Synthesis in Mammalian Cells Storage of Fatty Acids in Triacylglycerol... 

Karupaiah, T. and Sundram, K. (2007). Effects of stereospecific positioning of fatty acids in triacylglycerol structures in native and randomized fats a review of their nutritional implications. Nutrition Metabolism, 4,16. 

Procedures for pancreatic lipase use are described by Jensen and Pitas (1976) and for lipoprotein, lingual and hepatic lipases by Paltauf et al, (1974). Stereospecific analysis of fatty acids in triacylglycerols has been fully discussed by Brecken-ridge (1978). 

Conjugated Fatty Acids in Triacylglycerols (% of total fatty acids)... 

Stereospecific Distribution of Fatty Acids in Triacylglycerols. It has been carried out by an adaptation of the procedures devised by Brockerhoff (1967) and Christie Moore (1969). 

Regarding the stereospecific distribution of fatty acids in triacylglycerols in relation to the positional distribution in phosphoglycerides, it can be stated that oleic acid is randomly distributed in the three positions of triacylglycerols from eggs... 

To obtain further information on the participation of the various positions of the glycerol moiety in the acyltransferase mechanism, the stereospecific distribution of fatty acids in triacylglycerols obtained after incubating insect homogenates with labelled fatty acids was investigated. 

Table 2. Composition of usual and unusual fatty acids in triacylglycerols and other hpids of seed tissues and plant cell cultures...

Yoshida, H., Tomiyama, Y, Yoshida, N., Shibata, K. andMizushina, Y. (2010) Regiospe-cific profiles of fatty acids in triacylglycerols and phospholipids from Adzuki beans (Vigna angularis). Nutrients 2, 49-59. 

Examples of these compounds are P-sitosteryl pahnitate (3-127), P-D-glucopyranosyl-P-sitosterol (3-128) and its ester with palmitic acid (3-129). In sunflower oil, for example, the amount of steroids is 0.32%, 0.07% of steroids occur as esters, 0.03% as glycosides and the rest are free sterols. Fatty acids bound in sterol esters are mainly palmitic, stearic, oleic, linoleic and linolenic acids, but the fatty acid composition of sterol esters may not match the composition of fatty acids in triacylglycerols. 

Unsaturated fatty acids bound in phospholipids can be oxidised by oxygen, similarly to fatty acids in triacylglycerols. Phospholipid hydroperoxides may react with amino groups of other phospholipids and other amino compounds to form dark brown macromolecular products similar to melanoidins (see Section 4.7.5.7) formed in the Maillard reaction. Therefore, phospholipids act as synergists (among other mechanisms) of... 

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