Lecithins hydrolysis

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. 

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. 

An earlier procedure for the production of choline and its salts from natural sources, such as the hydrolysis of lecithin (23), has no present-day apphcation. Choline is made from the reaction of trimethyl amine with ethylene oxide [75-21-8] or ethylene chlorohydrin [107-07-5J. 

Lecithinase is produced by Clostridium perfringens. This is a calcium-dependent lecithinase whose activity depends on the ability to split lecithin. Since lecithin is present in the membrane of many different kinds of cells, damage can occur throughout the body. Lecithinase causes the hydrolysis of erythrocytes and the necrosis of other tissue cells. 

Ester hydrolysis Lecithin vesicles and CTABr micelles. Vesicles inhibited reaction Fatah and Loew, 1983... 

Figure 4.12 Hydrolysis of a phospholipid (lecithin) in the lumen by a phospholipase. Lysolecithin is a lysophospholipid and is a detergent. At high concentrations it can damage membranes. It is also produced during repair of damaged phospholipids (Chapter 11)...

T6. The Action of Phospholipases The venom of the Eastern diamondback rattler and the Indian cobra contains phospholipase A2, which catalyzes the hydrolysis of fatty acids at the C-2 position of glycerophospholipids. The phospholipid breakdown product of this reaction is lysolecithin (lecithin is phosphatidylcholine). At high concentrations, this and other lysophospholipids act as detergents, dissolving the membranes of erythrocytes and lysing the cells. Extensive hemolysis may be life-threatening. 

Influence of Intermolecular Spacing on Enzymic Hydrolysis of Lecithin Monolayers. When snake venom phospholipase A is injected under a lecithin monolayer, it splits lecithin into lysolecithin and free fatty acid. The change in polar groups of the monolayer results in a change of surface potential. However, if prior to injection of enzyme into the subsolution, a lecithin monolayer is compressed to such a surface pressure that the active site of the enzyme is unable to penetrate the monolayer, hydrolysis does not proceed. For monolayers of dipalmitoyl, egg, soybean, and dioleoyl lecithins the threshold surface pressure values at which hydrolysis does not proceed are 20, 30, 37, and 45 dynes per cm., respectively (40). This is also the same order for area per molecule in their surface pressure-area curves, indicating that enzymic hydrolysis of lecithin monolayers is influenced by the unsaturation of the fatty acyl chains and hence the intermolecular spacing in monolayers (40). 

Enzymic hydrolysis of lecithin monolayers is strikingly influenced by the degree of unsaturation of fatty acyl chains and hence by the intermolecular spacing in monolayers. 

Lecithins and related phospholipids usually contain a saturated fatty acid in the C-l position but an unsaturated acid, which may contain from one to four double bonds, at C-2. Arachidonic acid is often present here. Hydrolysis of the ester linkage at C-2 yields a l-acyl-3-phosphoglycerol, better known as a Iysophosphatidylcholine. The name comes from the powerful detergent action of these substances which leads to lysis of cells. Some snake venoms contain phospholipases that form Iysophosphatidylcholine. Lysophosphatidic acid (l-acyl-glycerol-3-phosphate) is both an intermediate in phospholipid biosynthesis (Chapter 21) and also a signaling molecule released into the bloodstream by activated platelets.15... 

The phosphoric acid esters of diacyl glycerides, phospholipids, are important constituents of cellular membranes. Lecithins (phosphatidyl cholines) from egg white or soybeans are often added to foods as emulsifying agents or to modify flow characteristics and viscosity. Phospholipids have very low vapor pressures and decompose at elevated temperatures. The strategy for analysis involves preliminary isolation of the class, for example by TLC, followed by enzymatic hydrolysis, derivatization of the hydrolysis products, and then GC of the volatile derivatives. A number of phospholipases are known which are highly specific for particular positions on phospholipids. Phospholipase A2, usually isolated from snake venom, selectively hydrolyzes the 2-acyl ester linkage. The positions of attack for phospholipases A, C, and D are summarized on Figure 9.7 (24). Appropriate use of phospholipases followed by GC can thus be used to determine the composition of phospholipids. 

In some cases separation of lecithins from phosphatidyl ethan-olamines and phosphatidyl serines is carried out prior to enzymatic hydrolysis. Composition of the phospholipids is virtually always determined finally by GLC of their fatty acid methyl esters. 

Penetration of electrolytes into both the air-water interface and films of dipalmitoyl lecithin is accompanied by a relatively small surface potential increase, whereas hydrolysis of CaCl% produces accumulation of Ca(OH)t and related species at the interface (l). Although in the absence of ionic lipids a correlation between interfacial ionic populations of the electrolyte and the surface potential changes is not yet possible, the marked surface potential effects of CaCU accompanying the presence of small quantities of acidic phospholipids in dipalmitoyl lecithin films suggest that the acidic lipid contaminants are still the only certifiable species whose interaction with CaCl2 produces an appreciable surface potential increase. Surface radioactivity and IR absorption spectra of dipalmitoyl lecithin in the presence of CaCU produced no evidence of Ca -dipalmitoyl lecithin interaction. 

Subbaiah, P. V., Chen, C. H., Albers, J. J., and Bagdade, J. D., Studies on the cofactor requirement for the acylation and hydrolysis reactions catalyzed by purified lecithin icholesterol acyltransferase Effect of low density lipoproteins and apolipoprotein A-I. Atherosclerosis 45, 181-190 (1982). 

Alternatively, the enzyme may be used in an encapsulated form. Chen and Chang (1993) showed that hydrolysis of milk fat by lipase from Candida cyclindracea encapsulated in reverse micelles formed by soybean lecithin in isooctane, could be manipulated to favor the release of short-chain fatty acids by using a higher concentration of enzyme and a higher ratio of water to surfactant concentration at 45°C. 

Chen, J.-P., Chang, K.-O. 1993. Lipase-catalyzed hydrolysis of milk fat in lecithin reverse micelles. J. Ferment. Bioeng. 76, 98-104. 

Phospholipase A2 Obtained from porcine pancreatic tissue. Produced as a white to tan powder or pale to dark yellow liquid. Major active principle phospholipase A2. Typical application used in the hydrolysis of lecithins. 

Phospholipase A2 Hydrolysis of lecithins and phosphatidylcholine, producing fatty acid anions. 

Most enzymes are inactive when the water activity falls below 0.85. Such enzymes include amylases, phenoloxidases, and peroxidases. However, lipases may remain active at values as low as 0.3 or even 0.1 (Loncin et al. 1968). Acker (1969) provided examples of the effect of water activity on some enzymic reactions. A mixture of ground barley and lecithin was stored at different water activities, and the rates of hydrolysis were greatly influenced by the value of a (Figure 1-27). When the lower a values were changed to 0.70 after 48 days of... 

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). 

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. 

Hydrolyzed lecithin. Crude lecithin is readily hydrolyzed in the presence of strong acids or bases. Enzymes can be used for very selective hydrolysis. Prolonged treatment leads to fatty acids, glycerophosphoric acid, or their salts, with mixtures of amino compounds and carbohydrates (4, 115). 

Haas et al. (162) have studied enzymatic phosphatidylcholine hydrolysis in organic solvents by examining selected commercially available lipases. Enzymatic hydrolysis of oat and soy lecithins, and its effect on the functional properties of lecithin, was investigated by Aura et al. (163). The phospholipase used was most effective at low enzyme and substrate concentrations. 

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