Lecithin degradation

Diehl, B. W. K., Ockels, W. and Woydt, D. (1994) Kinetics in lecithin degradation. 84th AOCS Annual Meeting and Exposition, Atlanta, GA, May copy available from author. 

Woydt, D. (1994) Kinetics in Lecithin Degradation. Diploma Thesis. Universitat Osnabriick, Germany. 

The identity of the moiety (other than glycerol) esterified to the phosphoric group determines the specific phosphoHpid compound. The three most common phosphoHpids in commercial oils are phosphatidylcholine or lecithin [8002-45-5] (3a), phosphatidylethanolamine or cephalin [4537-76-2] (3b), and phosphatidjlinositol [28154-49-7] (3c). These materials are important constituents of plant and animal membranes. The phosphoHpid content of oils varies widely. Laurie oils, such as coconut and palm kernel, contain a few hundredths of a percent. Most oils contain 0.1 to 0.5%. Com and cottonseed oils contain almost 1% whereas soybean oil can vary from 1 to 3% phosphoHpid. Some phosphoHpids, such as dipaLmitoylphosphatidylcholine (R = R = palmitic R" = choline), form bilayer stmetures known as vesicles or Hposomes. The bdayer stmeture can microencapsulate solutes and transport them through systems where they would normally be degraded. This property allows their use in dmg deHvery systems (qv) (8). 

For certain naturally occurring nontoxic a.i., an enforcement is not sensible (e.g., lecithin, rape seed oil). Analytical methods for residues in soil are not necessary if the DTgo values of the a.i. and relevant metabolites are less than 3 days (e.g., fosetyl), because in general, the results from residue analyses are not meaningful if the a.i. is rapidly degraded. 

Phospholipids containing phosphatidyl, inositol, lecithin, serine, and ethanolamine (Stevenson 1986) are the second most abundant identifiable form of organic P in the upper layer of the subsurface. These groups contain glycerol, fatty acids, and phosphate (Sims and Pierzjinski 2005). The P in the structure is a diester, which is more susceptible to degradation in soils than monoesters. 

Another associated issue was the possibility of inactivating the LRES (lym-phoreticuloendothelial system). By analogy with other injectable systems, it could also be deduced that the injectable emulsion system needed to be sterile and apy-rogenic and free of acute or chronic toxicities from components or their associated degradation products. It also followed that the injectable system required to be stable, although how stability was to be determined and, more to the point, measured, has remained an issue to the present day. This is mainly because emulsions are thermodynamically unstable although their stability can be extended by formulation. As a result emulsion products are now available that are submicron in diameter, sterile, and stable for several years after preparation. In major part this has been due to the use of phospholipids as stabilizers and emulsifiers, in particular the mixed products identified as the lecithin of commerce. 

Domingo et al. evaluated immobilization of trichloroethylene-degrading Burkholderia cepacia bacteria using hydrophilic polyurethane foam. The influences of several foam formulation parameters upon cell retention were examined. Surfactant type was a major determinant of retention a lecithin-based compound retained more cells than Pluronic- or silicone-based surfactants. 

JD Weete. Preferential degradation of noncholine phosphatides in soybean lecithin by thermalization. J Am Oil Chem Soc 71 1195-1199, 1994. 

Enhancement of matrix degradation Polyunsaturated lecithins Colchicine Adenosine Collagenase activity... 

AS/. The AV is the number of milligrams of potassium hydroxide necessary to neutralize the acids in 1 g of lecithin (62). A product s AV is representative of the acidity contributed by both the phospholipids and any free fatty acids that are present. The AV is usually not indicative of pH, as the chemical nature of the phospholipid imparts buffering quahties to most systems. Lecithins typically exhibit a neutral pH value in aqueous media. An AV above 36 may indicate degradation of the lecithin because of improper processing or substandard quality soybeans. AV should not be confused with free fatty acid content, pH, or mineral acids. The correct method to assay for free fatty acids is to titrate only the acetone-soluble portion of the lecithin, whereby any contribution from the phospholipids in the acetone-insoluble portion is eliminated. AV is determined by the AOCS Official Method Ja 6-55 (77). 

Moisture. The water content of lecithin products is usually less than 1.0%. As a consequence of lecithin s essentially moisture-free state, lecithin products have very low water activity and do not adversely contribute to the microbiological profile of most food systems. Most lecithin products are preserved well in storage. Higher moisture levels usually indicate a greater potential for spoilage or chemical degradation. Moisture is determined by AOCS Official Method Ja 2b-87 (77). A less accurate moisture level can also be determined by azeotropic toluene distillation (AOCS Official Method Ja 2-46) (77). One cannot determine lecithin moisture by vacuum oven methods. These methods are known to degrade lecithin products and yield false moisture levels. 

Lecithins decompose at extreme pH. They are also hygroscopic and subject to microbial degradation. When heated, lecithins oxidize, darken, and decompose. Temperatures of 160-180°C will cause degradation within 24 hours. 

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... 

Phosphatidylcholines, above all lecithin, occur in millimolar concentrations in serum and bile. Acetylcholine (ACh) occurs in brain and nerve extracts together with its degradation product, choline. 

Enzymes and proteins that synthesize, transport, and hydrolyze CE are found both inside and outside of cells. In most cases, the intracellular and extracellular enzymes use entirely different cofactors, and have different pH optima. The enzymes found within cells typically include both a CE-synthesizing enzyme, acyl-CoA cholesterol acyltransferase (ACAT), and 2 or 3 CE-degrading enzymes acid CE hydrolase (CEH), neutral CEH, and possibly a mitochondrial CEH. Blood plasma and the extracellular fluid, on the other hand, contain only a CE-synthesizing enzyme, lecithin cholesterol acyltransferase (LCAT), and a CE transfer protein (CETP). Finally, pancreatic juice contains a CE-degrading enzyme, pancreatic CEH. Each of these very different proteins is discussed below, with the exception of pancreatic CEH, which is discussed in Chapter 5. 

Figure 117. Effect of a liposome formulation on the degradation of procaine (pH 10.2, 40°C). Lecithin concentration o 0 1.01 x 10 2M (Reproduced from Ref. 487 with permission.)...

The naturally occurring anti-inflammatory agent in egg-yolk was later identified as iV-(2-hydroxyethyl)palmitamide , and shown to be identical with a crystalline fraction prepared from arachis oil and soya bean lecithin which is active at 0-3 g/kg in the guinea-pig anaphylactic arthritis test . It is not active, however, in a cotton-pellet test or in a capillary permeability test in rats. When the compound is degraded, anti-allergic activity resides in... 

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