Diacylglycerol-containing polar lipids

Linoleic (>30%), oleic (>18%), and Unolenic (2-12%) acids are the most predominant unsaturated fatty acids present (9). Lemon, lime, and citron oils contain the highest amount of linolenic acid. In addition, very small amounts of myr-istoleic acid (C14 l) in polar lipids fraction, myristoleic (C14 l) and palmitoleic (C16 l) acids in diacylglycerols fraction, and myristoleic (C14 l) and eicosaenoic (C20 l) acids in triacylglycerols fraction of citms seed oil were also identified (39). 

The egg contains lipids on a large scale, even in its outer region. The shell contains 0.045% lipids in the cuticula and 1.35% lipids in the shell membrane (Suyama et al., 1977). Neutral and polar lipids occur in proportions of 5 1 and 6 1, respectively. Neutral lipids consist of mono-, di-, and triacylglycerols (TAG), cholesterol and cholesteryl esters, and free fatty acids (EA). The main components in the neutral lipid fraction of the shell and its adjoining layers are cholesterol and cholesteryl esters, in addition to diacylglycerols the TAG content is low. 

According to Oomah et al. (1996), extraction of residual oil from commercially available flaxseed meal with hexane alone resulted in a higher oil recovery than methanol/hexane or methanol-ammonia-water/hexane. However, it should be noted that their starting material was meal and not seeds of flax. Analysis of the extracted lipids from the meal showed (Table 3) that hexane preferentially extracted the neutral lipids primarily composed of triacylglycerols (TAG). Neutral lipid fraction of oil extracted with methanol/hexane solvent system contained more monoacylglycerols (MAG), diacylglycerols (DAG) and free fatty acids (FFA) than the lipids extracted by other solvent systems (Table 3). Methanol/hexane solvent system extracted more polar lipids than methanol-water-am-monia/hexane system and this lipid fraction was composed mainly of phosphotidylcholine (PC). Polar lipids of methanol-ammonia-water/hexane extracted lipids contained also phosphotidylethanolamine (PE), lysophosphatidylcholine (LPC) and some unidentified compounds. 

TLC procedures with silica gel G layers (containing calcium sulfate as binder) have been employed most frequently for lipid class separations. Commonly, the solvent elution system used is hexane- diethyl ether-formic acid (80 20 2 by volume), and this gives the separations shown in Figure 2.6. Cholesterol esters migrate to the solvent front, and they are followed by triacylglycerols, free fatty acids, cholesterol, diacylglycerols, monoacylglycerols and phospholipids (with other polar lipids). For small-scale preparative... 

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