Lecithin chemical hydrolysis

Nonspecific Phosphoesteroses. These enzymes cleave a variety of phosphoric acid derivatives, even synthetic substrates and lecithins (diesters of phosphoric acid with glycerol and choline). Such enzymes occur among other places in snake venom, and in the intestinal mucosa. Snake venom phosphatases specifically split 3 -phos-phate bonds, giving rise to 5 -monophosphates, whereas chemical hydrolysis yields a mixture of the 2 - and 3 -monophosphates. Free 3 -phosphate groups (the monoesters) are inhibitory in the enzymic reaction. 

In principle chemical hydrolysis of the fatty acids from the phospholipid molecules is possible. However, this reaction is not applied on a plant seale, because enzymatic hydrolysis is the preferred state-of-the-art process. Chemical partial hydrolysis can be made with various strong acids, but the modified lecithins usually have a dark brown to black colour, forming an obstacle for successful industrial use in many applications. 

The simplest method for modifying natural (crude) lecithin is the addition of a non-reactive substance. Plastic lecithins are converted to fluid forms by adding 2% to 5% fatty acids and/or carriers such as soybean oil. If the additives react with the lecithin to alter the chemical structure of one or more of the phospholipid components, the resulting product is referred to as a chemically modified lecithin. Modification can also be achieved by subjecting lecithin to partial controlled enzymatic hydrolysis. Finally, refined lecithin products can be obtained by fractionating the various phospholipid components. 

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). 

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. 

None of the venoms, however, showed any interaction with films of cholesterol or protein, nor did hydrolysis occur in films of tripalmitin, triolein, cerebron, or sphingomyelin. The reaction with lecithin is highly specific. Not only is it sensitive to the chemical structure of the film, but the reaction rate may also be greatly altered by slight changes in the orientation of the molecules in the film or by changes in the pH of the solution or of the concentration of venom. 

Dry Powder Systems Dry powder formulations are susceptible to a number of potential interactions. Since there is currently only one approved excipient, the drugs have to be compatible with lactose 4 In addition, dry powders are prone to moisture sorption, which can give rise to chemical degradation by hydrolysis or physical instability due to capillary forces.44 As other excipients, such as lecithin, are explored as excipients in dry powder products, a hydrophobic effect... 

When chromatography on activated adsorbents is employed chemical alterations of lipids are possible. Renkonen (1962) reported hydrolysis of lecithin on aluminium oxide columns. Because of the danger of isomerization and oxidation solvents have to be carefully purified. 

These compounds are members of a broader group of chemical substances called lipids, which has been classified by the National Research Council into (1) nonpolar lipids— including esters of fatty acids (triacylglycerols and cholesteryl esters) that are virtually insoluble in water but soluble in most organic solvents, and enter metabolic pathways only after hydrolysis and (2) polar or amphi-pathic lipids—including fatty acids, cholesterol, sphingolipids, and glycerophospholipids (mainly lecithins). The term phospholipids... 

Properties such as large interfacial area and an ability to solubilize both oil-soluble and water-soluble reactants in a single phase system makes microemulsions ideal as reaction media (Flanagan and Singh, 2006 Gaonkar and Bagwe, 2002). For example, Morgado and co-workers (1996) nsed a continnons reversed micellar system to synthesize lysophospholipids and free fatty acids from lecithin hydrolysis, with applications to the food, pharmaceutical and chemical industries. Hydrolysis was catalyzed by porcine pancreatic phospholipase A. Carvalho and Cabral (2000) reviewed the use of reversed micellar systems as reactors to carry out lipase-catalyzed esterification, biocatalysis, transesterificadon, and hydrolysis reactions. 

HPLC is the most common technique applied to the determination of the chemical composition of lecithin. Normal phase HPLC is convenient for the determination of the major constituents (i.e., phosphatidylcholine, phosphatidylethanolamine, etc), as described in Chapter 7. P NMR is also suitable for this analysis, as discussed in Chapter 14. The biochemical literature contains many enzymatic methods, mainly for specific determination of phosphatidylcholine and its hydrolysis product, choline (32). For instance, phosphatidylcholine can be hydrolyzed by phospholipase C to a diacylglycerol and the phosphate ester of choline, which itself can be hydrolyzed by alkaline phosphatase to form choline and phosphate ion. Alternatively, action of phospholipase D on phosphatidylcholine yields phosphatidic acid and choline. These methods are not applied to analysis of the commercial lecithin used as a surfactant. 

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