Fatty acid positional distribution

Fatty Acid Positional Distributions in Triacylglycerols from Various Sources... 

Camielli, V.P., Luijendijk, I.H.T., van Beek, R.H.T., Boerma, G.J.M., Degenhart, H.J. and Sauer, P.J.J. (1995). Effect of dietary triacylglycerol fatty acid positional distribution on plasma lipid classes and their fatty acid composition in pre-term infants. American Journal of Clinical Nutrition, 62, 776-781. 

Lien, EL. The role of fatty acid positional distribution infants. J Pediatr, 1994 125 S62-8. 

Yli-Jokipii, K.M., Schwab, U.S., Tahvonen, R.L., Kurvinen, J.P, Mykkanen, H.M. and Kallio, H.P., Triacylglycerol molecular weight and to a lesser extent, fatty acid positional distribution, affect chylomicron triacylglycerol composition in women. J. Nutr, 132, 924—929 (2002). 

The distribution of fatty acids in phospholipids is not random, with saturated fatty acids preferentially occupying position 1 and unsaturated fatty acids position 2. 

The chemical interesteriflcation process results in the fatty acids being distributed randomly, unlike those of natural oils and fats. The advantage of having the 16 0 fatty acids in the 1- and/or 3-position is eliminated. It will therefore be more difficult to keep interesterified fats in the P form. 

Sohd fats may show drastically different melting behavior. Animal fats such as tallow have fatty acids distributed almost randomly over all positions on the glycerol chain. These fats melt over a fairly broad temperature range. Conversely, cocoa has unsaturated fatty acids predominantly in the 2 position and saturated acids in the 1 and 3 positions. Cocoa butter is a brittle sohd at ambient temperature but melts rapidly just below body temperature. 

Cholesterol (Figure 14-17) is widely distributed in all cells of the body but particularly in nervous tissue. It is a major constituent of the plasma membrane and of plasma lipoproteins. It is often found as cholesteryl ester, where the hydroxyl group on position 3 is esteri-fied with a long-chain fatty acid. It occurs in animals but not in plants. 

As can be seen in Table 4.2, the fatty acids are not randomly distributed among the three positions of the TG in bovine milk. Control of esterification is not understood, but there are several factors known to affect it. The presence of glucose is known to stimulate the synthesis of milk TG (Dimmena and Emery 1981 Rao and Abraham 1975). In the mouse, Rao and Abraham concluded that glucose was supplying factors other than NADPH or acylglycerol precursors that stimulated milk fat synthesis. The fatty acid that is esterified is known to be affected by the concentration of the acyl donors present (Marshall and Knudsen 1980 Bickerstaffe and Annison 1971). However, in studies under various conditions, palmitic acid was consistently esterified at a greater rate than other fatty acids (Bauman and Davis 1974 Moore and Christie 1978 Smith and Abraham 1975). 

Triacylglycerols. The composition of TGs refers to their structure or the identity of the fatty acids esterified to each of the three hydroxyls on glycerol and ultimately to the identity of the individual molecular species. Because there may be over 400 fatty acids in a milk sample, based on random distribution, there may be a total of 4003 or 64 x 106 individual TGs, including all positional and enantiomeric isomers. A random distribution is defined as all possible combinations resulting from expansion of the binomial equation. If we have two fatty acids, x and y, located at random in the three positions of glycerol, the equation becomes (x + y)3 or x3 + 3x2y + 3 xy2 + y3, which, when expanded further, is x3 = xxx, 3x2y = xxy, 3 xy2 = yyx, y3 = yyy yxx xyy... 

Parodi s (1979, Table 4.3) data again indicate the asymmetric distribution of fatty acids. The percentage of a fatty acid at position sn-3 generally decreased with an increase in the chain length of the acid, with the reverse occurring at position sn-1. There was no major vari-... 

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