Unsaturated lecithins

Phospholipid vesicles (and bilayers) composed of phospholipids with well-defined fatty acid side chains undergo a sharp transition from a crystallinelike state to an amorphous state as the temperature is raised.107 The transition temperature depends on the nature of the fatty acid side chains. For example, for C12 saturated fatty acid chains on lecithin the transition temperature is 0° and for C18 saturated fatty acid chains it is 58°C for unsaturated lecithins the transition temperature is below zero.107 For real membranes sharp phase transitions are not observed, because of the heterogeneous composition of the membrane. In the case of /3 hydroxybutyrate dehydrogenase, the enzymic activity apparently is not influenced by this phase transition as judged by the temperature dependence of the reaction rate. However, for some membrane-bound proteins, a plot of the reaction rate versus the reciprocal temperature... 

Saturated lecithins can be separated from the mercuric acetate adducts of unsaturated lecithins, on silica gel G, using chloroform-methanol-water (70 +30 + 4) [14]. 

Saturated lecithins and the three types of aldehydic cores obtained by reductive ozonolysis of unsaturated lecithins can be separated through reversed phase partition chromatography [168]. Fig. 147 shows photo-densitometric curves from thin-layer chromatograms of fission products derived from the lecithins of egg, bovine spinal cord, soya bean and wheat germ. 

Triglycerides and esters of diols (diol lipids), compounds which cannot be separated by adsorption TLC, can be fractionated into classes through reversed phase partition TLC this applies equally to the corresponding alkoxylipids [9]. Chromatography on hydrophobic layers is also suitable for separating the aldehydic cores which are obtained from unsaturated lecithins by reductive ozonolysis [168] (see Fig. 147, p. 409) and for analysing sphingosine bases [129]. 

Hydroxyl tion. Commercial lecithin can be hydroxylated at the unsaturated fatty acid chains by treatment with concentrated hydrogen peroxide and acids like lactic or acetic acid. 

Other Reactions of Phospholipids. The unsaturated fatty acid groups in soybean lecithin can be halogenated. Acetic anhydride combined with the amino group of phosphatidylethanolamine forms acetylated compounds. PhosphoHpids form addition compounds with salts of heavy metals. Phosphatidylethanolamine and phosphatidjhnositol have affinities for calcium and magnesium ions that are related to interaction with their polar groups. 

The yolk is separated from the white by the vitelline membrane, and is made up of layers that can be seen upon careful examination. Egg yolk is a complex mixture of water, Hpids, and proteias. Lipid components iaclude glycerides, 66.2% phosphoUpids, 29.6% and cholesterol [57-88-5] 4.2%. The phosphohpids consist of 73% lecithin [8002 3-5] 15% cephahn [3681-36-7], and 12% other phosphohpids. Of the fatty acids, 33% are saturated and 67% unsaturated, including 42% oleic acid [112-80-1] and 7% linoleic acid [60-33-3]. Fatty acids can be changed by modifying fatty acids ia the laying feed (see... 

Particular phospholipids display characteristic transition temperatures (Tm). As shown in Table 9.1, increases with chain length, decreases with unsaturation, and depends on the nature of the polar head group. For pure phospholipid bilayers, the transition occurs over a narrow temperature range. The phase transition for dimyristoyl lecithin has a peak width of about 0.2°C. 

Studies of the reaction of ozone with simplified lipid systems have shown that malonaldehyde can be produced by direct ozonolysis. The use of malonaldehyde assay as an index of lipid peroxidation is therefore invalid in ozone studies. Liposomes formed from egg lecithin and prepared in aqueous media were quite resistant to ozone, but the contribution of polyconcentric spheres to this resistance has not been fully assessed. However, the bilayer configuration, with the susceptible unsaturated fatty acids shielded from ozone by the hydrophilic areas of the molecule, may be resistant. In hexane, where the fatty acid moieties are exposed, ozone reacts stoichiometrically with the double bonds. The experiments with aqueous suspensions of phosphatidylcholine gave no evidence of the formation of lipid peroxides,nor did experiments with films of fatty acids exposed to ozone. ... 

Studies are currently underway in Moscow on the suitability of using sodium caseinate nanoparticles as carriers for phosphatidylcholine (lecithin) containing > 80% unsaturated fatty acids (oleic, linoleic, linolenic). In particular, it has been established that phosphatidylcholine oxidation can be reduced, or effectively eliminated altogether, in dispersed systems containing complexes with the protein (see Figure 2.4). 

The unsaturated phospholipid from soybean lecithin also shows a similar effect, while the unsaturated phospholipids from red blood cell membranes, although showing a slight effect of cholesterol interaction, still show a prominent polymethylene peak in the high resolution spectrum. 

Lecithin Monolayers. We have shown from surface pressure—area and surface potential-area curves of various lecithins that the molecular area increases and the interaction with metal ions decreases with increasing unsaturation of the fatty acyl chains (41, 43). 

Influence of Intermolecular Spacing on Enzymic Hydrolysis of Lecithin Monolayers. When snake venom phospholipase A is injected under a lecithin monolayer, it splits lecithin into lysolecithin and free fatty acid. The change in polar groups of the monolayer results in a change of surface potential. However, if prior to injection of enzyme into the subsolution, a lecithin monolayer is compressed to such a surface pressure that the active site of the enzyme is unable to penetrate the monolayer, hydrolysis does not proceed. For monolayers of dipalmitoyl, egg, soybean, and dioleoyl lecithins the threshold surface pressure values at which hydrolysis does not proceed are 20, 30, 37, and 45 dynes per cm., respectively (40). This is also the same order for area per molecule in their surface pressure-area curves, indicating that enzymic hydrolysis of lecithin monolayers is influenced by the unsaturation of the fatty acyl chains and hence the intermolecular spacing in monolayers (40). 

The interaction of metal ions with lecithin monolayers, as measured by the increase in surface potential, decreases with increasing unsaturation of fatty acyl chains. The phosphate and trimethylammonium groups of a lecithin molecule form an internal salt linkage which dissociates upon... 

Enzymic hydrolysis of lecithin monolayers is strikingly influenced by the degree of unsaturation of fatty acyl chains and hence by the intermolecular spacing in monolayers. 

The apparent condensation of mixed monolayers of lecithin in the presence of cholesterol is explained by a consideration of molecular cavities or vacancies caused by thermal motion of fatty acyl chains, the height of these cavities being influenced by the length, inclination, and degree of unsaturation (especially the proportion of monounsaturation) of the fatty acyl chains and the extent of compression of the monolayer. Mono-layers are liquefied by the presence of unsaturated fatty acyl chains or by the addition of cholesterol. 

Lecithins and related phospholipids usually contain a saturated fatty acid in the C-l position but an unsaturated acid, which may contain from one to four double bonds, at C-2. Arachidonic acid is often present here. Hydrolysis of the ester linkage at C-2 yields a l-acyl-3-phosphoglycerol, better known as a Iysophosphatidylcholine. The name comes from the powerful detergent action of these substances which leads to lysis of cells. Some snake venoms contain phospholipases that form Iysophosphatidylcholine. Lysophosphatidic acid (l-acyl-glycerol-3-phosphate) is both an intermediate in phospholipid biosynthesis (Chapter 21) and also a signaling molecule released into the bloodstream by activated platelets.15... 

Glycerophospholipids contain a glycerol skeleton to which two fatty acids are esterified saturated fatty acids occupy mostly sn-position 1, whereas unsaturated fatty acids are mainly present on sn-position 2. The third hydroxyl is linked to a phosphate group to which an organic base is mostly esterified (Fig. 1). The most important components of soybean lecithin are phosphatidylcholine (PC), phosphatidylethanolamine (PE), and phosphatidylinositol (PI). Phosphatidic acid (PA) may become important due to the presence of phospholipase D this enzyme slowly converts PC into PA in vegetable lecithins. Phosphatidylserine (PS), phosphatidylglycerol (PG), and lyso-phosphatidylcholine (LPC) are known as minor components lysophospholipids contain only one acyl group per molecule. Besides, ether phospholipids occur in which one or both fatty acyl... 

Cohen, D.E. and Carey, M.C. 1991. Acyl chain unsaturation modulates distribution of lecithin molecular species between mixed micelles and vesicles in model bile. Implications for particle structure and metastable cholesterol solubilities. J. Lipid Res. 32, 1291-1302. 

CH2li2 6rl5i ,w3.M+, or alkyl caboxylates H(Cih n W2-M+ withn typically 7-15 and M+ an alkali metal cation, generally sodium, or they may be anionic, such as H(CH2- 12 3+C1- or H(CH2 12 3 3+C1-. The alkyl chains need not be normal i.e., they may be branched, and may be fluorine-substituted. Some natural surfactants are also of importance e.g., lecithins such as 1,2-diacyl glycero-3-phosphate, with the acyl groups being H(CH2 an< n typica-Hy 12 18, the latter possibly oleyl, i.e., unsaturated. 

Oxidation of nicotinamide Oxidation of unsaturated fatty acids Oxidation of lecithin... 

Extracted from the bean and often called Soyabean oil. A versatile carrier suitable for all skin types. It is comparatively high, up to 17%, in unsaturated fatty acids with the unsaturated linoleic (54%), oleic (24%), palmitic (10%), linolenic (7%) and stearic (4%). It also contains the highest amount of lecithin of any vegetable oil and the cold pressed oil is particularly high in vitamin E. It needs careful storage as it oxidizes easily. Soya oil may cause allergic reactions and has been reported to damage hair. 

Besides phospholipid composition, the main difference between plant/legume lecithin (e.g., soy) and lecithin in egg yolk is that the former has a higher unsaturated fatty acid content and no cholesterol. Egg lecithin as a commercial ingredient, with the exception of some medical feeding programs, is too expensive for routine use in food (10). In some infant formulas, egg yolk lipids and egg lecithin are used (22). 

Lecithin can be fractionated from cottonseed as phospholipids and glycolipids. Cottonseed lecithin shows flavor and color deterioration when blended with other vegetable oils. The saturated/unsaturated fatty acid ratio of cottonseed phospholipids is approximately 1 2 (39). Palmitic acid constitutes 90% of the total saturated fatty acids (36%), and linoleic acid is approximately 80% of the total unsaturated fatty acids (64%). Gossypol binds to lecithin during oil extraction from glanded cottonseed (approximately 9% in cmde phospholipids). This economically negates its... 

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