Triacylglycerol saturated

Mortimer, B.C., Holthouse, DJ., Martins, I.J., Stick,R.V., and Redgrave, T.G. (1994) Effects of Triacylglycerol-Saturated Acyl Chains on the Clearance of Chylomicron-Like Emulsions from the Plasmaof Rats, Biochim. Biophys. Acta 1211,171-180. 

Keywords Palmitic acid, palm oil, triacylglycerol, saturated fatty acid, dietetic fatty acid... 

The physical and chemical properties of individual oils and fats are determined by the nature and proportions of fatty acids that enter into the triglycerides composition. Animal and dairy fat like plant oils are dominated by triacylglycerols, with steroids present as minor components, cholesterol and its esters being the most significant. The triacylglycerols of animal fats differ from plant oils since they contain more of the saturated fatty acids and consequently are solid at room temperature. 

Gas chromatography (GC or, less commonly, GLC) is the most widely used separation technique for volatile samples. The resolution is sufficient to routinely separate components, such as homologous series, saturated from unsaturated fatty acids, terpenoids, triacylglycerols, etc. The use of a mass spectrometer to identify the separated components (GC-MS) is discussed in Section 8.4. 

Waxes are biosynthesized by plants (e.g., leaf cuticular coatings) and insects (e.g., beeswax). Their chemical constituents vary with plant or animal type, but are mainly esters made from long-chain alcohols (C22-C34) and fatty acids with even carbon numbers dominant (Fig. 7.11). They may also contain alkanes, secondary alcohols, and ketones. The majority of wax components are fully saturated. The ester in waxes is more resistant to hydrolysis than the ester in triacylglycerols, which makes waxes less vulnerable to degradation, and therefore more likely to survive archaeologically. 

Saturated hydrocarbons Unsaturated hydrocarbons Wax esters Steryl esters Long chain aldehydes Triacylglycerols Long chain alcohols Free fatty acids Quinones Sterols... 

Figure 7.9 The degradation of triaq/lglycerol in adipose tissue to fatty acids and glycerol. The figure indicates the progressive release of fatly acids and the types of fatty acid that are usually present at each position and, therefore, released from each position as the triacylglycerol molecule. Sat. - Saturated. A lipase that is not regulated by hormones is also present is adipose tissue. It is continually active. Its role is described below.

Figure 11.7 Synthesis of triaq/lglyceroL The precursors are glycerol 3-phosphate and long-chain acyl-CoA. R, is a saturated fatty acid, R2 is an unsaturated fatty acid (one or two doubte bonds) and R3 is either saturated or unsaturated. The activity of GPAT-1 regulates triacylglycerol synthesis. In all reactions involving RCO.SCoA, the CoASH is released but is not shown in this diagram. P,- - phosphate.

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 first steps of glycerophospholipid synthesis are shared with the pathway to triacylglycerols (Fig. 21-17) two fatty acyl groups are esterified to C-l and C-2 of L-glycerol 3-phosphate to form phosphatidic acid. Commonly but not invariably, the fatty acid at C-l is saturated and that at C-2 is unsaturated. A second route to phosphatidic acid is the phosphorylation of a diacyl-glycerol by a specific kinase. 

Structure of triacylglycerols (TAG) The three fatty acids esterified] to a glycerol molecule are usually not of the same type. The fefy I acid on carbon 1 is typically saturated, that on carbon 2 is typi-j cally unsaturated, and that on carbon 3 can be either. Recall thal the presence of the unsaturated fatty acid(s) decrease(s) thl I melting temperature of the lipid. An example of a TAG molecule H shown in Figure 16.12. 

Monounsaturated fats Triacylglycerols containing primarily fatty acids with one double bond are referred to as monounsaturated fat. Unsaturated fatty acids are generally derived from vegetables and fish. When substituted for saturated fatty acids in the diet, monounsaturated fats lower both total plasma cholesterol and LDL cholesterol, but increase HDLs. This ability of monounsaturated fats to favorably modify lipoprotein levels may explain, in part, the observation that Mediterranean cultures, with diets rich in olive oil (high in monounsaturated oleic acid), show a low incidence of coronary heart disease. 

LDL—but little change in HDL—when compared with a typical Western diet higher in saturated fats. Plasma triacylglycerols are unchanged. 

Prepare a table listing the retention time for each standard FAME. Use this table to identify the fatty acids present in each triacylglycerol you analyzed. Alternatively, plot the log of the retention time against the chain length of each saturated FAME (see Figure E6.5). Unknown saturated fatty acids can be identified from experimental retention times using this plot. Unsaturated fatty acids cannot be identified from the plot of saturated FAMEs. A separate plot of log retention time vs. the chain length must be prepared for each level of saturation (saturated, monounsaturation, diunsaturation, etc.). 

All of the described procedures use emulsified substrate. Although the p-nitrophenyl laurate assay cocktail is stable for 3 days at 4°C, the emulsified olive oil substrates (or other triacylglycerol-based substrate systems) should be made fresh daily and rehomogenized periodically and when separation is visually evident. Use of day-old emulsion substrate will yield increased blank values for titratable acidity, and this effectively compromises the limit of detection of activity. Emulsified substrates should be in liquid form at common assay conditions (20° to 50°C), and partially solidified substrates (those rich in long-chain saturated fatty acids) will cause interfacial irregularities and confound the assessment of lipases in ways that cannot be accounted for. 

The chromatographic profiles representing saturated mono-, di-, and polyunsaturated long-chain fatty acid esters from marine triacylglycerols were very complex. In general, polyunsaturates are eluted before saturates of equal chain length and shorter-chain before longer-chain fatty acid esters. 

Fig. 29 Separation of triacylglycerols from sunflower seed oil by HPLC with a silver ion column and mass detection. For conditions see text. S = saturated fatty acid M = monounsaturated fatty acid D = di-unsaturated fatty acid.

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