Hydrogenation unsaturated phospholipids

Hydrogenation of unsaturated phospholipids dispersed in aqueous systems using a water-soluble homogeneous catalyst was first reported in 1978 [22], The catalyst was a sulfonated derivative of Wilkinson s catalyst which did not appear to affect the structure of bilayers with respect to their permeability barrier properties [23]. The catalyst was found to hydrogenate oil-in-water emulsions and two-phase oil/water systems without the need for organic co-solvents [24]. 

The hydrogenation of phospholipid-bound unsaturated fatty acids by a homogeneous, water-soluble, palladium catalyst, Biochim.Biophys.Acta 92 1 (1987) 167-174... 

Figure D1.6.6 latroscan TLC-FID chromatograms of (A) a lipid fraction enriched with neutral lipids isolated from cod flesh and stored in ice (B) neutral lipids spiked with authentic 1 -0-palmityl-glyceryl ether dipalmitate (GE), coinciding in position with authentic highly unsaturated acids such as 22 6n-3 (C) hydrogenated neutral lipids spiked with GE. The solvent system was 97 3 1 (v/v/v) hexane/diethyl ether/formic acid for 40 min. Abbreviations O, origin SF, solvent front FFA, free fatty acid PL, phospholipids SE, steryl ester ST, free sterol TG, triglyceride. Reproduced from Ohshima et al. (1987) with permission from AOCS Press.

Canola Oil occurs as a light yellow oil. It is typically obtained by a combination of mechanical expression followed by n-hexane extraction, from the seed of the plant Brassica juncea, Brassica napus, or Brassica rapa (Fam. Cruciferae). The plant varieties are those producing oil-bearing seeds with a low erucic acid (C22 i) content. It is a mixture of triglycerides composed of both saturated and unsaturated fatty acids. It is refined, bleached, and deodorized to substantially remove free fatty acids phospholipids color odor and flavor components and miscellaneous, other non-oil materials. It can be hydrogenated to reduce the level of unsaturated fatty acids for functional purposes in foods. It is a liquid at 0° and above. 

The physical properties of bilayers depend on their phase, which is determined by the transition temperature (Tm) of the bilayer lipid mixture. The Tm depends on the nature of the head group, the length and the degree unsaturation of the fatty acid chains and the interaction between the lipid molecules (higher Tm is obtained when hydrogen bonds are formed between phospholipid bead groups) [30]. 

Figure 1 Hydrolysis of ester linkages in glvcerophospholipids bv phospholipases Ai. A . C and D. The fatty acid at the sn-1-position (Ri) is usually saturated while that at the sn-2-position (R2) is unsaturated. R3 varies in different phospholipids and could be choline (phosphatidylcholine), ethanolamine (phosphatidylethanolamine), serine (phospha-tidylserlne), myoinositol (phosphatidylinositol), myoino-sitol-4-monophosphate (phosphatidylinositol-4-monophosphate) or myoinositol-4,5-blsphosphate (phosphatidylinositol-4,5-bisphosphate). In phosphatidic acid, R3 is a hydrogen atom.

Various refined, modified or otherwise processed grades of commercial lecithin are available (e.g. fractionated, phosphorylated, acylaled, hydroxylated and hydrogenated), with consequent differences in composition and physical properties. Liquid, plastic or free-flowing forms can be made. Modified lecithins can function as both oil-in-water and water-in-oil emulsifiers. Hydrogenated varieties have reduced proportions of unsaturated carbon chains in the phospholipids, and are therefore more stable towards oxidation (Table 12.46). 

Fatty acids in which hydrogen is substituted by other elements have also been employed. lodination of an unsaturated fatty acid yields an iodine-tagged molecule which has been used to study fat deposition and phospholipide transport. - Such a tagged molecule is, however, unphysi-... 

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