Lecithin decomposition

Commercial lecithin is insoluble but infinitely dispersible in water. Treatment with water dissolves small amounts of its decomposition products and adsorbed or coacervated substances, eg, carbohydrates and salts, especially in the presence of ethanol. However, a small percentage of water dissolves or disperses in melted lecithin to form an imbibition. Lecithin forms imbibitions or absorbates with other solvents, eg, alcohols, glycols, esters, ketones, ethers, solutions of almost any organic and inorganic substance, and acetone. It is remarkable that the classic precipitant for phosphoHpids, eg, acetone, dissolves in melted lecithin readily to form a thin, uniform imbibition. Imbibition often is used to bring a reactant in intimate contact with lecithin in the preparation of lecithin derivatives. 

Hydrolysis. The first effect of either acid hydrolysis or alkaline hydrolysis (saponification) is the removal of the fatty acids. The saponification value of commercial lecithin is 196. Further decomposition into glycerol, phosphoric acid, and head groups (ie, choline, ethanolamine, etc) may foUow prolonged heating. Lecithin may also be hydrolyzed by enzymes. 

Fig. 3.4. Microtiter plate UV spectra taken in in acceptor wells. The weighted residuals plots triplicate of propranolol reference, donor, and indicate that the shapes of spectra in donor acceptor solutions, at iso-pH 7.4 in 20% wt/vol and acceptor wells are in agreement with those soy lecithin in dodecane. (a) After 15 h per- in the reference wells, confirming that neither meation time, surfactant-free (b) 3 h, 35 mM decomposition nor impurities were detectable.

Storage and handling. Liquid lecithin can be kept for years provided closed containers are used and the temperature does not exceed 20-25°C. Bleached products require more careful storage and handling. Color reversion will occur rapidly in bleached products, particularly at elevated temperatures. Decomposition of peroxide is thought to contribute to color reversion in bleached products. In order to prevent this phenomenon, low storage temperatures are recommended (115). 

As obtained from brain-tissue lecithin is a colorless or faintly yellowish, imperfectly crystaUine solid, or sometimes of a waxy consistency. It is very hygroscopic. It does not dissolve in H,0, ia wbicb, however, it swells up and forms a mass like starch-paste. It dissolves in alcohol or ether, very sparingly in the cold, but readily under the influence of heat. It dissolves in chloroform and in benzol Lecithin is very prone to decomposition, particularly at slightly elevated temperatures its chloride combines with PtCl to form aa insoluble yellowish chloroplatinate. 

One of the first of the putrid alkaloids to be formed in cadaveric matter is choline (see pp. 207, 273), which undoubtedly has its origin in the decomposition of the lecithins. 

It is produced during the first twenty-four to forty-eight hours of putrefaction of animal tissues, from the decomposition of the lecithins, and diminishes from the third day, when other ptomains (neuridin, putrescin, cadaverin) increase in amount. It has been obtained synthetically by the action of trimethylamin upon ethylene oxid, or upon ethylene chlorhydrin. When heated, it splits up into glycol and trimethylamin. Nitric acid converts it intu muscariu. 

When an alcoholic solution of lecithin is brought into contact-with hot solution of barium hydroxid it yields barium glycerophosphate, barium stearate, and cholin (see p. 276). This decomposition indicates the constitution of lecithin and its relations to the fats. Glycerophosphoric acid is phosphoric acid in which an atom of hydrogen has been replaced by the univalent i-emalnder CHaOH- CHOH—CHa—left by the removal of OH from, glycerol ... 

Liposomes composed of phosphatidylcholine, cholesterol, and dl-(-tocopherol improved shelf life of vitamin C from a few days up to 2 months, especially in the presence of common food components which normally speed up decomposition, such as copper ions, ascorbate oxidase, and lysine (Kirby et al 1991). Calcium lactate was also encapsulated in lecithin liposomes, in this case to prevent undesirable calcium-protein interactions (Champagne and Fustier, 2007). The liposomal calcium levels of fortified soymilk were equivalent to those found in cow s milk. A synergistic effect of coencapsulation of vitamins A and D in liposomes promoted calcium absorption in the GI tract (Champagne and Fustier, 2007). 

Phospholipids contribute specific aroma to heated milk, meat and other cooked foods through lipid oxidation derived volatile compounds and interaction with Maillard reaction products. Most of the aroma significant volatiles from soybean lecithin are derived from lipid decomposition and Maillard reaction products including short-chain fatty acids, 2-heptanone, hexanal, and short-chain branched aldehydes formed by Strecker degradation (reactions of a-dicarbonyl compounds with amino acids). The most odor-active volatiles identified from aqueous dispersions of phosphatidylcholine and phos-phatidylethanolamine include fra 5 -4,5-epoxy-c/5-2-decenal, fran5,fran5-2,4-decadienal, hexanal, fra 5, d5, d5 -2,4,7-tridecatrienal (Table 11.9). Upon heating, these phospholipids produced cis- and franj-2-decenal and fra 5-2-undecenal. Besides fatty acid composition, other unknown factors apparently affect the formation of carbonyl compounds from heated phospholipids. 

The fatty acid components of the phosphatides in lecithin may be characterized by gas chromatographic analysis. Depending on the objective of the study, either the total sample or isolated individual phosphatides are analyzed. Sample preparation may consist of saponification followed by formation of the methyl esters for GC analysis. More often, decomposition and formation of methyl esters occurs simultaneously in a transesterifica-tion reaction with BF3/methanol, HCl/methanol, or sodium methoxide (109,110). 

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