Phospholipids and lecithin

Bile, pH 7.8-8.6, is produced continuously in humans. Hepatic bile is concentrated and stored in the gall bladder between meals. It is ejected from the gall bladder and flows into the duodenum when food enters the intestine. The main constituents of bile are bile salts, bilirubin, end products of hemoglobin breakdown, the electrolytes sodium, chloride, and bicarbonate, cholesterol, phospholipids, and lecithin. The gall bladder contracts within 30 min after eating due to liberation of cholecystokinin. The most effective stimulus to this is food high in fat. 

A typical biomembrane consists largely of amphiphilic lipids with small hydrophilic head groups and long hydrophobic fatty acid tails. These amphiphiles are insoluble in water (<10 ° mol L ) and capable of self-organization into uitrathin bilaycr lipid membranes (BLMs). Until 1977 only natural lipids, in particular phospholipids like lecithins, were believed to form spherical and related vesicular membrane structures. Intricate interactions of the head groups were supposed to be necessary for the self-organization of several ten thousands of... 

LEH is primarily composed of a combination of saturated high-carbon phospholipids and cholesterol. Synthetic phospholipids replaced hydrogenated soy lecithin when the latter was found to induce several untoward biological responses (40). Current choice of a saturated high-carbon phospholipid is mostly between distearoyl phosphatidylcholine (DSPC, 55°C) and... 

In the bile cholesterol is kept soluble by fats, phospholipids like lecithin and by bile acids. The important bile acids in human bile are cholic acid, chen-odeoxycholic acid or chenodiol and ursodeoxycholic acid or ursodiol. Bile acids increase bile production. Dehydrocholic acid, a semisynthetic cholate is especially active in this respect. It stimulates the production of bile of low specific gravity and is therefore called a hydrocholeretic drug. Chenodiol and ursodiol but not cholic acid decrease the cholesterol content of bile by reducing cholesterol production and cholesterol secretion. Ursodiol also decreases cholesterol reabsorption. By these actions chenodiol and ursodiol are able to decrease the formation of cholesterolic gallstones and they can promote their dissolution. 

As an example of an asymmetric membrane integrated protein, the ATP synthetase complex (ATPase from Rhodospirillum Rubrum) was incorporated in liposomes of the polymerizable sulfolipid (22)24). The protein consists of a hydrophobic membrane integrated part (F0) and a water soluble moiety (Ft) carrying the catalytic site of the enzyme. The isolated ATP synthetase complex is almost completely inactive. Activity is substantially increased in the presence of a variety of amphiphiles, such as natural phospholipids and detergents. The presence of a bilayer structure is not a necessary condition for enhanced activity. Using soybean lecithin or diacetylenic sulfolipid (22) the maximal enzymatic activity is obtained at 500 lipid molecules/enzyme molecule. With soybean lecithin, the ATPase activity is increased 8-fold compared to a 5-fold increase in the presence of (22). There is a remarkable difference in ATPase activity depending on the liposome preparation technique (Fig. 41). If ATPase is incorporated in-... 

There are six common grades of lecithin available including fractionated lecithins. Fractions with different phosphatidylcholine content are commercially available. Besides these common commercial grades, more special products are available, e g., enzymatically modified lecithin and phospholipids, semisynlhelic phospholipids, and acetylaled lecithins. 

R Szucs, K Verleysen, GS Duchateau, P Sandra, BGM Vandeginste. Analysis of phospholipids in lecithins. Comparison between MEKC and HPLC. J Chromatogr A 738 25-29,1996. 

Two main types of lipids occur in biological membranes phospholipids and sterols. The predominant phospholipids in most membranes are phosphoglycerides, which are phosphate esters of the three-carbon alcohol, glycerol. A typical structure is that of phosphatidylcholine (lecithin) ... 

The structure of the interfacial layers in food colloids can be quite complex as these are usually comprised of mixtures of a variety of surfactants and all are probably at least partly adsorbed at interfaces which even individually, can form complex adsorption layers. The layers can be viscoelastic. Phospholipids form multi-lamellar structures at the interface and proteins, such as casein, can adsorb in a variety of conformations [78]. Lecithins not only adsorb also at interfaces, but can affect the conformations of adsorbed casein. The situation in food emulsions can be complicated further by the additional presence of solid particles. For example, the fat droplets in homogenized milk are surrounded by a membrane that contains phospholipid, protein and semi-solid casein micelles [78,816], Similarly, the oil droplets in mayonnaise are partly coated with granular particles formed from the phospho and lipo-protein components of egg yolk [78]. Finally, the phospholipids can also interact with proteins and lecithins to form independent vesicles [78], thus creating an additional dispersed phase. 

In initial work, L- a-phosphatidylcholine (lecithin) from egg yolk was selected as the phospholipid, and later studies compared other phospholipids and lipid extracts from meat. As the study originated from investigations of cooked meat flavor, the model system reactions were carried out in aqueous solution buffered with phosphate at an initial pH of 5.7 and concentrations of the reactants were selected to approximate their relative compositions in mammalian muscle. The reactions were carried out under pressure... 

Phospholipids are components of lecithins, and within this complex mixture6 they have been applied to the skin since the earliest days of cosmetics. Phosphatidylcholines (PCs) are the most abundant of phospholipids in lecithins and in the majority of biological membranes. PCs in pure form are used in the pharmaceutical and the cosmetic industries. Toxicological aspects of PCs in topical use have been reviewed recently7. Two different forms of PC are used by the cosmetic industry today ... 

A surfactant molecule is an amphiphile, which means it has a hydrophilic (water-soluble) moiety and a hydrophobic (water-insoluble) moiety separable by a mathematical surface. The hydrophobic tails of the most common surfactants are hydrocarbons. Fluorocarbon and perfluorocarbon tails are, however, not unusual. Because of the hydrophobic tail, a surfactant resists forming a molecular solution in water. The molecules will tend to migrate to any water-vapor interface available or, at sufficiently high concentration, the surfactant molecules will spontaneously aggregate into association colloids, i.e., into micelles or liquid crystals. Because of the hydrophilic head, a surfactant (with a hydrocarbon tail) will behave similarly when placed in oil or when put in solution with oil and water mixtures. Some common surfactants are sodium or potassium salts of long-chained fatty acids (soaps), sodium ethyl sulfates and sulfonates (detergents), alkyl polyethoxy alcohols, alkyl ammonium halides, and lecithins or phospholipids. 

Many phospholipids contain an additional alcohol esterified to the phosphoric acid group. Cephalins are esters of ethanolamine, and lecithins are esters of choline. Both cephalins and lecithins are widely found in plant and animal tissues. 

Figure 4 shows the results of determined droplet diameters according to equations (3) and (5) for the high pressure atomisation of raw lecithin (app. 2/3 insoluble phospholipids and 1/3 soluble lecithin oil) and for crude soy oil (app. 1 w.-% insoluble phospholipids) by the two extraction pressures of 48 MPa and 70 MPa. 

Lecithin-based o/w MEs for parenteral use were formulated using polysorbate 80, IPM (Isopropyl myristate), lecithin, and water at different lecithin-polysorbate 80 weight ratios [115]. The formulated systems were shown to be highly stable and of minimal toxicity when evaluated in vitro. Phospholipid-based ME formulations of all-trans retinoic acid (ATRA) for parenteral administration were prepared and tested in vitro [116]. ATRA is effective against acute promyelocytic leukemia with highly variable oral bioavailability. Parenteral ME of ATRA was prepared using pharmaceutically acceptable ingredients, namely phospholipids and soybean oil. The inhibitory effect of ATRA on two human cancer cell lines (HL-60 and MCF-7) was not affected by incorporation into a ME formulation. 

Choline is an essential component of phospholipids - phosphatidylcholine (lecithin) is the major phospholipid in cell membranes and sphingomyelin is important in the nervous system. Acetylcholine is a transmitter in the central and parasympathetic nervous systems and at neuromuscular junctions, and has a role in the regulation of differentiation and development of the nervous system (Biagioni et al., 2000). Acetylcholine is also synthesized in mononuclear lymphocytes, where it has an autocrine or paracrine role in regulating immune function (Fujii and Kawashima, 2001). 

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). 

A wide range of data has been published showing the variability in the composition of phospholipids and fatty acids in soybean lecithin (Tables 6 and 7) (32). Older data were often determined by qualitative TLC, whereas today 31P-NMR, quantitative Li-Sc HPLC, and HPTLC methods have been developed. 

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... 

---