Lecithins acetylation

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. 

FIGURE 9. Endogenous lipoprotein metabolism. In liver cells, cholesterol and triglycerides are packaged into VLDL particles and exported into blood where VLDL is converted to IDL. Intermediate-density lipoprotein can be either cleared by hepatic LDL receptors or further metabolized to LDL. LDL can be cleared by hepatic LDL receptors or can enter the arterial wall, contributing to atherosclerosis. Acetyl CoA, acetyl coenzyme A Apo, apolipoprotein C, cholesterol CE, cholesterol ester FA, fatty acid HL, hepatic lipase HMG CoA, 3-hydroxy-3-methyglutaryl coenzyme A IDL, intermediate-density lipoprotein LCAT, lecithin-cholesterol acyltransferase LDL, low-density lipoprotein LPL, lipoprotein lipase VLDL, very low-density lipoprotein. 

Transfer of a phosphocholine residue to the free OH group gives rise to phosphatidylcholine (lecithin enzyme l-alkyl-2-acetyl-glycerolcholine phosphotransferase 2.7.8.16). The phosphocholine residue is derived from the precursor CDP-choline (see p. 110). Phos-phatidylethanolamine is similarly formed from CDP-ethanolamine and DAG. By contrast, phosphatidylserine is derived from phosphatidylethanolamine by an exchange of the amino alcohol. Further reactions serve to interconvert the phospholipids—e.g., phosphatidylserine can be converted into phosphatidylethanolamine by decarboxylation, and the latter can then be converted into phosphatidylcholine by methylation with S-adenosyl methionine (not shown see also p. 409). The biosynthesis of phosphatidylino-sitol starts from phosphatidate rather than DAG. 

Acetylcholine is an ester composed of acetate (from acetyl coenzyme A) and choline (either synthesized de novo or taken in the diet as lecithin). The enzyme choline acetyl transferase catalyzes the reaction to form Ach. The breakdown of Ach back to acetate and choline, which will terminate its activity, is catalyzed by the enzyme acetylcholineesterase (Achase). 

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. 

Commercial lecithin is produced by water degumming (precipitation from oil with ion-exchange treated water), separation by stacked disk centrifuge, and vacuum drying to less than 1 percent moisture content. Crude lecithins contain 70-72 percent acetone insolubles (AI) and are standardized to 62-64 percent and an acid value of 30 by addition of oil and fatty acids before sale. Crude lecithins may be treated with acetone to obtain free-flowing powders with 95-98 percent AI. Lecithin can be additionally purified, bleached, fractionated, hydrogenated, hydrox-ylated, acetylated, sulfonated, and halo-genated.104 One domestic company makes 13 kinds of lecithin for food uses alone. 

Native or hydrogenated palm, palm kernel, rapeseed, soya, pemiut, coconut, castor, cotton oils, cocoa butter and their derivatives (obtained by fractionation, esterification, concentration mid/or reconstitution fatty acids mid cohols, mono-, di- and triglycerides, cocoa butter substitutes, mmgmine, shortenings, acetylated glycerides, lecithins, etc)... 

Soybean lecithins can be chemically altered to modify their emulsifying properties and improve their dispersibihty in aqueous systems. Phospholipids may be hydrolyzed by acid, base, or enzyme to achieve better hydrophilic and emulsification properties. Hydroxylation of lecithin improves its oil-in-water emulsification property and water dispersibihty. Acetylation creates improved fluidity and emulsification, water dispersion properties, and heat stability (200). 

A method for classifying lecithin to include modified and refined forms has been proposed by Cowell et al. (55). This classification distinguishes between natural (crude) lecithins and those modified by either custom blending or chemical/enzy-matic treatment, e.g., hydroxylation, hydrogenation, acetylation, or refining by acetone or alcohol fractionation. These latter products reflect the state of the art regarding the availability of the various lecithin products on the market and have enhanced properties for specific uses. A listing of soybean lecithin classifications follows (56). 

Modified lecithins. Lecithins may be modified chemically, e.g., hydrogenation, hydroxylation, acetylation, and by enzymatic hydrolysis, to produce products with improved heat resistance, emulsifying properties, and increased dispersibility in aqueous systems (7, 58, 59). One of the more important products is hydroxylated lecithin, which is easily and quickly dispersed in water and, in many instances, has fat-emulsifying properties superior to the natural product. Hydroxylated lecithin is approved for food applications under Title 21 of the Code of Federal Regulations 172.814 (1998) (60). 

Fluidization with phosphoric acid is not recommended because darkening of the product and hydrolysis may occur. Degumming with acetic anhydride results in fluidized lecithins possibly because PE is acetylated by the reagent. Nonedible lecithins may be fluidized by the addition of acidulated and dried soapstock. 

Cmde lecithin contains a number of functional groups that can be successfully hydrolyzed, hydrogenated, hydroxylated, ethoxylated, halogenated, sulfonated, acylated, succinylated, ozonized, and phosphorylated, to name just a few possibilities (1). The only chemically modified food-grade products produced in significant commercial quantities at the present time are the ones obtained by hydroxylation, acetylation, and enzymatic hydrolysis (58). Hydroxylated or acylated lecithins represent chemical modifications to improve the functionality in water-based systems. 

The total acetone insolubles content of commercial acetylated lecithin products can vary from about 52% to about 97%, the remainder being soybean oil (or another food-grade triglyceride or fatty acid as a natural constituent or added diluent), natural pigments, sterols, and other minor constituents present in crude lecithin from the soybean. The acetylated lecithin meets all the compositional requirements of the U.S. Food Chemicals Codex (54). 

Minimally Acetylated, Commercial, Liquid Lecithin Specification... 

Acetylated lecithins have improved fluid properties, improved water dispersibility, and are effective oil-in-water emulsifiers for a wide variety of food formulations (56, 58). Moderately and highly acetylated lecithins are resistant to heat and can be repeatedly heated and cooled without darkening. The intended uses for minimally acetylated products are in infant foods, coffee whiteners, meat sauces, and gravies, and for oil-in-water cosmetic emulsions. Moderately and maximally acetylated products are used in cheese sauces, release agents in pumpable and aerosol formulations, and shortenings. 

The following patents have been issued on the topic of making and using acetylated lecithins ... 

As stated previously, moderately and highly acetylated lecithins exhibit heat-resistant properties that are very desirable to have in many release agent applications (173). A natural crude lecithin is subject to thermally induced reactions that are responsible for the darkening and formation of insolubles that occur after prolonged heating. There are several viscosity grades of heat-resistant lecithins available, and lecithin viscosity varies with temperature. Low-viscosity lecithins can be easily sprayed without dilution, or prepared as part of a spray release system. 

Oi-lipoproteins based on their electrophoretic migration. HDL transports cholesterol esters derived from the action of lecithin-cholesterol-acetyl transferase (LCAT). They are further differentiated into HDL2a, HDL2b and HDL3 on the basis of their varying densities and protein moiety. (29) (s. fig. 3.8)... 

By using a surface radioactivity technique, the penetration of the hydrophobic and flexible 1-14C-acetyl--casein and the rigid and globular 1-14C-acetyl-lysozyme molecules into phospholipid monolayers in different physical states was monitored. The adsorption of ff-casein to lecithin mono-layers is described by a model in which it is assumed that the protein condenses the lecithin molecules so that the degree of penetration is a function of the lateral compressibility of the phospholipid monolayer. The interaction of ff-casein with phospholipid monolayers is dominated by the hydrophobicity of the macromolecule, but lysozyme tends to accumulate mostly beneath phospholipid monolayers in this situation, electrostatic interactions between the lipid and protein are important. 

Figure 2. Steady-state surface pressure (tt) as a function of the final substrate concentrations of 1-14C-acetyl-[3-casein for adsorption with stirring to the air-water interface (X), an egg lecithin mono-layer spread to an initial film pressure of 10 dynes/cm (O), and a dibehenoyl lecithin monolayer spread to an initial film pressure of 10 dynes/cm ( ). Substrate phosphate buffer (pH 7,1= 0.1) at...

Figure 4. Dependence of change in surface pressure (Air) and surface concentration (r) of 1 -14C-acetyl-/3-casein on the initial plm pressure (VJ of egg lecithin and dihehenoyl lecithin monolayers. The Air (A) and r (O) data for egg lecithin monolayers were obtained with an initial substrate concentration (Cj) of p-casein of 5 4 X 10r5 %. The Air (X) and r ( ) data for dihehenoyl lecithin monolayers were obtained with Cp1 — 10 4 %. The other conditions are described in Figure 2.

Figure 6. Variation of A7r and r for 1-14C-acetyl-lysozyme (Cp = 5.6 X 10 5 %) adsorbing to various lipid monolayers at = 10 dynes/cm. Substrate was phosphate buffer (pH 7, I = 0.1), and the monolayers were egg lecithin (PC), egg phosphatidyleihanolamine (PE), ox brain phosphatidylserine (PS), dicetyl phosphate (DCP)y and arachidic acid.

CE = cholesterol esters TG = triglycerides LPL = lipoprotein lipase FFA = free fatty acids apo CD cofactor for LPL apoAl = cofactor for LCAT LCAT = lecithin cholesterol acetyl transferase CETP = cholesterol ester transport protein... 

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