Triacylglycerols 606 INDEX

Transesterification, fatty acid analysis of lipids, 437, 439 Triacetin, lipase assays, 378 Triacylglycerol acylhydrolase, 371, 375, 378. See also Lipases Triacylglycerols, 432 Tributyrin, lipase assays, 378 Trichloroacetic acid (TCA) solubility index for protein hydrolysis, 152 in TBARS determination, 548-550 Trienes, conjugated, determination of, 515-517, 523-524, 526, 528 Trifluoroacetic acid (TFA), for determination of neutral sugars, 721-722, 724-725, 729-730... 

The major difficulty in the HPLC of triacylglycerols is that of detection. Traditional modes of detection, such as refractive index and ultraviolet absorbance, offer only low sensitivity toward these triacylglycerols. 

Fig. 41 Separation of triacylglycerols on Supelcosil-LC 8 with acetone-acetonitrile (70 30, v/v) as the mobile phase and refractive index detection. Flow rate, 1.0 ml/min. (a) Olive oil, (b) soybean oil, (c) sunflower oil, (d) corn oil.

Reversed-phase HPLC has been used to analyze the oxidation products of triacylglycerols in edible oils. The detection is often based on monitoring the conjugated dienes with an ultraviolet detector (234-235 nm). However, the UV detector provides no information about oxidation products without a conjugated diene structure, e.g., products of oleic acid. Information about these compounds is important when oils with a high oleic acid content are studied. The most common universal detector types—refractive index and flame ionization detectors—are not sensitive enough to detect small amounts of oxidation products. 

X PV +AV) being a better index of oxidation than either PV or AV alone. Volatile products can be removed from oils by deodorization, but aldehydes attached to the carboxyl end of the chain remain part of the triacylglycerol (sometimes called core aldehydes) and are indicators of previous oxidative damage. 

Slip point (ISO 6321, 2005) and solid fat index (AOCS method Cd 10-57, 2005) can provide information as to the suitability of an oil for use in manufacturing margarines and shortenings. Triacylglycerol (TAG) composition is an additional compositional analysis that can provide information on the potential functionality of an oil as well as its potential oxidative stability. Reversed-phase HPLC with various detection methods such as flame ionization, refractive index, evaporative light scattering, or atmospheric chemical ionization (coupled with mass spectrometry) can be used to determine TAG composition (Neff et d., 1994 Neff et al., 2001). 

Abbreviations BMI, body mass index TAG, triacylglycerol TC, total cholesterol HDL-C, high density lipoprotein cholesterol. 

Abbreviations DAG, diacylglycerol TAG, triacylglycerol BMI, body mass index LDL, low density lipoprotein HDL, high density lipoprotein. 

The separation of simple lipid classes from a lipid fraction aims to obtain distinct fractions of sterol esters, triacylglycerols, diacylglycerols, free sterols, free fatty acids, monoacylglycerols, and wax esters. There are numerous methods for lipid class separation, traditionally employing adsorption chromatography with silica gel columns, with increasing use currently of bonded phases such as the nitrile, diol, and polyvinylalcohol phases and of ELSD. These bonded phases give much better reproducibility of retention times than do the usual silica gel columns. Nevertheless, refractive index detection with silica gel columns and isocratic elution is still frequently employed for routine applications. 

However the activation of the A6 desaturation is shown later on. At 15 days it is very important. The apparent Km and Vm of the enz)mie are modified. This activation recovers the double bond index saturated acid ratio to 2.2 and is correlative to an increase of the triacylglycerol phosphatidyl choline ratio of the microsomes. Undoubtedly it is not correlative to the modification of the fatty acid composition of the membrane. Besides Ayala and Brenner have shown that the effect is not due to substrate deprivation (linoleate or a-linolenate) since rats fed on diets containing fish oil during 4 or 6 weeks have even lower A6 desaturation activity in liver microsomes than animals fed on sunflower seed oil compared to rats fed on EFA free diets (Table 2), Therefore the increase of the A6 desaturase activity in EFA deficiency is a physiological response of the cell to maintain the unsaturated/saturated acid ratio and fluidity of the membrane. 

BMI body mass index (kg/m ) SAD sagittal abdominal diameter Tonalin 22.6% trans- 0,cis- 2, 23.6% cis-l I and transA0jransA2, and 11.9% otho-CLA isomers FFAs free fady acids TAG triacylglycerol. ain... 

Carbohydrates with a high glycaemic index lead to a greater secretion of insulin after a meal than do those with a lower glycaemic index this results in increased synthesis of fatty acids and triacylglycerol (section 5.6.1), and is therefore a factor in the development of obesity (see Chapter 6). There is also some evidence that habitual consumption of carbohydrates with a high glycaemic index may be a factor in the development of non-insulin-dependent diabetes (section 10.7). 

There is certainly a benefit in reducing the intake of carbohydrates with a high glycaemic index (section 4.2.2), as these lead to a larger insulin response, and hence result in more triacylglycerol synthesis in response to insulin than an equivalent amount of carbohydrate with a low glycaemic index. 

Refractive index detectors also have several applications in lipid analysis. They are "universal" detectors, but lack sensitivity, require isocratic elution conditions and are sensitive to minor fluctuations in temperature. Their main value is probably in small-scale preparative applications, say with 1-2 mg of a lipid extract. For example, a refractive index detector was utilized with a column (4.6 x 250 mm) of Ultrasil Si (5 micron silica gel) and isocratic elution with isooctane-tetrahydrofuran-formic acid (90 10 0.5 by volume) to separate most of the common simple lipid classes encountered in animal tissue extracts, such as those of liver [304]. Cholesterol esters, triacylglycerols and cholesterol were each resolved and gave symmetrical peaks. 

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