Lecithins modification

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. 

The following commercial lecithin modifications were described in a publication from Central Soya Co., Inc. (168). 

Standard-grade (crude) lecithins are excellent water-in-oil emulsifiers. However, modified lecithins can function to emulsify either water-in-oU or oil-in-water emulsions, depending on the type of lecithin modification and the specific parameters of the system. These system parameters can include pH, types of components, component ratios, solids content, and others. Unlike crude lecithins, hydroxylated lecithins are stable in acid systems (pH 3.5). Fractionated lecithins can be manufactured for specific emulsion types. As lecithin s emulsifying activity is partially dependent on its phospholipid ratio, changing the ratio can alter its emulsifying capabilities (7). 

Fig. 9 Surface modification of cells with ssDNA-PEG-lipid. (a) Real-time monitoring of PEG-lipid incorporation into a supported lipid membrane by SPR. (r) A suspension of small unilamellar vesicles (SUV) of egg yolk lecithin (70 pg/mL) was applied to a CH3-SAM surface. A PEG-lipid solution (100 pg/mL) was then applied, (ii) Three types of PEG-lipids were compared PEG-DMPE (C14), PEG-DPPE (C16), and PEG-DSPE (C18) with acyl chains of 14, 16, and 18 carbons, respectively, (b) Confocal laser scanning microscopic image of an CCRF-CEM cell displays immobilized FITC-oligo(dA)2o hybridized to membrane-incorporated oligo(dT)20-PEG-lipid. (c) SPR sensorigrams of interaction between oligo(dA)2o-urokinase and the oligo (dT)2o-PEG-lipid incorporated into the cell surface, (i) BSA solution was applied to block nonspecific sites on the oligo(dT)20-incorporated substrate, (ii) Oligo(dA)20-urokinase (solid line) or oligo(dT)20-urokinase (dotted line) was applied...

It is possible to remove the soy bean oil in order to produce a de-oiled lecithin but in confectionery use there is little point in using a de-oiled product. Chemical modification of lecithins is possible but this would cause them to lose their natural status. Another way of modifying the properties is to fractionate the raw lecithin in order to yield products that are richer in one of the components. The resulting products, of course, retain their natural status. 

The most common modifications of lecithin and the intended physical/functional alterations are shown in Table 20 (31). The range of physical/functional properties available in commercial lecithins is listed in Table 21 (31). These changes in lecithin allow for the basic lecithin obtained from soybean oil to be converted to various emulsifier products having a wide variety of food, feed, and industrial applications. Reviews describing chemical reactions for phospholipid modifications intended to obtain specific functionalities include those of Eichberg (89), Hawthorn and Kemp (90), Kuksis (91), Pryde (86), Snyder (92), Strickland (87), and Van Dee-nen and DeHaas (93). 

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. 

As a variety of methods are available for modifying the emulsifying properties of commercial lecithin, the potential for improved, tailor-made, functional products is unlimited. The main functional properties are emulsification, antispatter, instantizing/wetting/dispersing, release/parting, viscosity modification, and baking applications. 

The manner in which lecithin is modified to achieve increased hydrophilicity will greatly affect its emulsification properties. Different modifications will create lecithin products with different apparent HLB (hydrophile-lipophile balance) values, a term used to convey the approximate degree of water dispersibility (hydrophilicity) of lecithin products (31). The higher its HLB value, the more water dispersible the lecithin product. In o/w emulsions, the type of fat to be emulsified may require a specific type of hydrophilic lecithin for optimum emulsion stability. Dashiell (31) provides a short listing of fat types, and the corresponding class of lecithin found to give the most stable emulsion in model systems of water/fat/ emulsifier. 

Confections. There are three major specific properties for lecithin in confections emulsification (e.g., caramels), anti-stick/release properties, and viscosity modification (e.g., chocolate) (175). None of these properties stand alone. For example, emulsification in caramels will influence shelf life and texture. In chocolate, viscosity modification will alter production costs and texture of the finished product. 

Water-dispersible lecithins are made by chemical modification, or by mixing ordinary lecithin with nonionic surfactants. Many of the products recommended in the literature and technical brochures for water-based compositions include such chemically modified, water-dispersible, lecithin compounds (e.g., hydroxy-lated, acylated, fractionated, and refined grades) (428, 431 33). Usually 0.5% to 1% modified lecithin is recommended in polyvinyl acetate-based paints, acrylic emulsions, and in butadiene—styrene emulsion paints. 

With the excellent release properties of lecithin, lubrication would seem like a natural area for its use. Indeed, lecithin has been used as an emulsifier to stabilize oil and water metal-cutting fluids (466). Incorporation of lecithin in the lubricant for forming sheet metal products can improve the electrostatic application properties of the lubricant, especially for food contact applications (467). Soaking valve seals in a solution containing lecithin impregnates the rubber and imparts improved lubrication (468). As with other areas discussed, modification of the lecithin for the... 

The liver synthesizes two enzymes involved in intra-plasmic lipid metabolism hepatic triglyceride lipase (HTL) and lecithin-cholesterol-acyltransferase (LCAT). The liver is further involved in the modification of circulatory lipoproteins as the site of synthesis for cholesterol-ester transfer protein (CETP). Free fatty acids are in general potentially toxic to the liver cell. Therefore they are immobilized by being bound to the intrinsic hepatic fatty acid-binding protein (hFABP) in the cytosol. The activity of this protein is stimulated by oestrogens and inhibited by testosterone. Peripheral lipoprotein lipase (LPL), which is required for the regulation of lipid metabolism, is synthesized in the endothelial cells (mainly in the fatty tissue and musculature). 

LeNeveu, D. M., Rand, R. P Gingell, D. Parsegian, V. A. (1976a). Apparent modification of forces between lecithin bilayers. Science 191, 399—400. 

Phosphatidylcholines are the most important fraction of soybean lecithin. Then-content may be increased by transesterihcation with choline hydrochloride, catalyzed by phospholipase D. Phosphatidylcholine content may thus be increased from 30% up to 60 or 70%, or from 75 or 80% to more than 90% (Juneja et ah, 1989). Similarly, phosphatidylserine can be produced from phosphatidylcholine by enzyme-catalyzed inter-esterification (Yaqoob et al., 2001). Another modification of lecithins is the inter-esterihcation of lysophosphatidylcholine with fish PUFA under catalytic action of phospholipase A2 (Na et al., 1990). 

After suitable modification it can be used as a solvent, a lubricant, and as biodiesel. Valuable by-products recovered during refining include lecithin, tocopherols, and phytosterols. Attempts to modify the fatty acid composition by seed breeding or genetic modification are directed to reducing the level of saturated acid or linolenic acid, or increasing the content of stearic acid. ... 

In this context. Let et al. suggested that the composition of the interface may be more important than the total surface area itself. In recent years, research focused on modification of the oil-water-interface with the aim of physical stabilization of the interface during dehydration and/or modification of the release of the encapsulated core material. A well-described system is stabilization of the interface through bilayer formation using lecithin as emulsifier and chitosan as oppositely charged polymer for bilayer formation. - Due to the cationic surface of the droplet, surface repulsion... 

Nature already produces the desired structures, and isolation of these components mostly requires only physical methods without chemical modification. Examples comprise polysaccharides (cellulose, starch, alginate, pectin, agar, chitin, and inuUn), disaccharides (sucrose and lactose), and triglycerides, lecithin, natural rubber, gelatin, flavors and fragrances, etc. 

The pretreatment of oils comprises the processes to which the oils are subjected prior to the removal of free fatty acids by either chemical or physical means. The purpose of the processing is either to recover phosphatides as the by-product lecithin or to remove from the oil impurities which will interfere with other refining or modification stages. 

The enzyme hydroxyacyl dehydrogenase described above is specific for the L-isomer. Apparently, some mammalian tissue can also oxidize the D-isomer, but it is not clear what enzymic mechanism is responsible for that reaction. Although the presence of an enzyme that specifically catalyzes the oxidation of the D-hy-droxyacyl ester to yield the keto acid has been proposed by some, others believe that the D-hydroxyacyl is transformed to the L-hydroxy acid by enzymes with racemase activity—namely, crotonase and another racemase. The equilibrium of the enzyme reaction is modified by the presence of magnesium in the medium. The modification of the equilibrium probably results from the complexion of magnesium with the keto acid. Eliminating the product favors the formation of the hydroxyacyl. Hydroxybutyrate can also be oxidized by an enzyme found in the mitochondria of many tissues, such as brain, kidney, heart, and liver. Hydroxybutyrate dehydrogenase has been isolated, solubilized, purified from beef heart, and demonstrated to require lecithin for activity. 

---