Crude lecithin

Commercial crude lecithin is a hrown to light yellow fatly substance with a liquid to plastic consistency. Its density is 0.97 g/niL (liquid) and 0.5 g/mL (granule). The color is dependent on its origin, process conditions, and whether it is unbleached, bleached, or Altered. Its consistency is determined chiefly by its oil. free fatty acid, and moisture content. Properly refined lecithin has practically no odor and has a bland taste. It is soluble in aliphatic and aromatic hydrocarbons, including the halogenated hydrocarbons however, it is only partially soluble in aliphatic alcohols. Pure phosphatidylcholine is soluble in ethanol,... 

Thin-layer chromatography of the crude lecithin on silica gel using chloroform revealed two main spots, the phosphatides at the origin and the triglycerides at 0.67 (sterol esters and pigments... 

Commercial lecithin is produced by water degumming (precipitation from oil with ion-exchange treated water), separation by stacked disk centrifuge, and vacuum drying to less than 1 percent moisture content. Crude lecithins contain 70-72 percent acetone insolubles (AI) and are standardized to 62-64 percent and an acid value of 30 by addition of oil and fatty acids before sale. Crude lecithins may be treated with acetone to obtain free-flowing powders with 95-98 percent AI. Lecithin can be additionally purified, bleached, fractionated, hydrogenated, hydrox-ylated, acetylated, sulfonated, and halo-genated.104 One domestic company makes 13 kinds of lecithin for food uses alone. 

Soybean lecithin is the predominant source of food and pharmaceutical lecithin because of its availability and outstanding functionality. The composition of crude soy lecithin is shown in Table 14. As a result of the presence of a large amount of neutral oil, crude lecithin is usually de-oiled to improve its functionality. De-oiling is based on the solubility difference of neutral and polar lipids in acetone, in which the phospholipids are precipitated and separated. Alcohol fractionation of de-oiled lecithin can further separate lecithin into an alcohol-soluble fraction that is enriched with phosphatidylcholine and an alcohol-insoluble fraction enriched with phospha-... 

Lecithin recovered from solvent-extracted soybean oil had different phospholipid class compositions from those produced by mechanical pressing (198). The percentage of phosphatidylcholine was considerably higher in lecithin recovered from extruded-expelled oU than from solvent-extracted oil. The phosphatidylcholine- and phosphatidylinositol-enriched fractions produced by ethanol extraction of the crude lecithin also showed different functional properties (199). 

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. 

A method for classifying lecithin to include modified and refined forms has been proposed by Cowell et al. (55). This classification distinguishes between natural (crude) lecithins and those modified by either custom blending or chemical/enzy-matic treatment, e.g., hydroxylation, hydrogenation, acetylation, or refining by acetone or alcohol fractionation. These latter products reflect the state of the art regarding the availability of the various lecithin products on the market and have enhanced properties for specific uses. A listing of soybean lecithin classifications follows (56). 

Natural (crude) lecithins. Specibcations as debned by the National Soybean Processors Association (1986-1987) for natural (crude) lecithins is presented in Table 15 (57). Specibcations have also been published by the Food Chemicals Codex (1996) (54). 

Fractionated and oil-free lecithins. When crude lecithin is further refined by various fractionation methods to selectively separate its components, acetone and ethanol are the most common solvents used. Fractionation of crude lecithin yielding phosphatidylcholine of greater than 90% purity is done commercially. 

HI. The level of HI matter is one measure of the purity of lecithin products. HI matter usually consists of residual fiber, but also particulate contaminants that may be introduced during processing (e.g., filter aids). The level of HI matter in crude lecithin should never exceed 0.3% and rarely exceeds 0.1%. HI matter in lecithin is detrimental to clarity and use in specific applications. HI is measured by an official Food Chemicals Codex (FCC) (1996) method (54) or by AOCS Official Method Ja 3-87 (77). 

Figure 3. Flowsheet for degumming soybean oil and crude lecithin production (111).

Fluidizing. Fluidizing additives such as soybean oil, fatty acids, or calcium chloride can be added to adjust the viscosity. The viscosity of dried crude lecithin can also be decreased by warming it to a maximum of 60°C. The dried crude lecithin product (unbleached or bleached) can also be used to prepare a variety of grades of lecithin by removing the oil to increase the phospholipid content, or by separating the oil-free lecithin into alcohol-soluble and alcohol-insoluble fractions. 

Depending on the type and efficiency of the extraction equipment, the acetone/ crude lecithin ratio necessary to achieve a 95% phospholipid product is 10-20 1 (v/v). In batch extraction, the tank is charged with acetone prior to crude lecithin... 

In a continuous extraction, crude lecithin and acetone are simultaneously metered into a vessel. Within limits, acetone consumption can be decreased by increasing residence time in the continuous extractor, increasing raw material efficiency (33). 

When compared with crude lecithin, oil-free lecithin is more hydrophilic and seems to have better emulsifying activity than its A1 alone would suggest. The removal of odor/flavor components with the oil also produces blander lecithins (7). 

The total acetone insolubles content of commercial acetylated lecithin products can vary from about 52% to about 97%, the remainder being soybean oil (or another food-grade triglyceride or fatty acid as a natural constituent or added diluent), natural pigments, sterols, and other minor constituents present in crude lecithin from the soybean. The acetylated lecithin meets all the compositional requirements of the U.S. Food Chemicals Codex (54). 

Hydroxylation of lecithin is carried out by the reaction of crude lecithin with hydrogen peroxide and lactic acid or acetic acid. Active sites for peroxidation appear to be double bonds as measured by IV drop and the isolation of dihydrox-ystearic acid from the reaction mixtures. Hydroxylation is allowed to proceed until... 

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). 

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). 

General food applications of lecithin include margarine, confections, snack foods, soups, instant foods, bakery products, simulated dairy products, processed meat/poultry/seafood products, and dietary apphcations. The most widespread uses of crude lecithin products are in confections and margarine (7, 174). 

As stated previously, moderately and highly acetylated lecithins exhibit heat-resistant properties that are very desirable to have in many release agent applications (173). A natural crude lecithin is subject to thermally induced reactions that are responsible for the darkening and formation of insolubles that occur after prolonged heating. There are several viscosity grades of heat-resistant lecithins available, and lecithin viscosity varies with temperature. Low-viscosity lecithins can be easily sprayed without dilution, or prepared as part of a spray release system. 

Many companies sell crude lecithin gums to the feed industry with httle or no further processing. However, the full nutritional and functional advantages of phospholipid use in animal feeds can be obtained through exploitation of the different types of lecithins available (313). 

Care is taken not to overheat the oil, for prolonged heating of some oils, like cottonseed, sets the color and produces a permanently dark oil (158). The clarified, desolventized oil usually is degummed to remove the phospholipids. This ensures better oil quality if the oil is sold to firms that further process the oil. The gums are added to the marc going through the desolventizer. This raises the oil level of the extracted meal a few percentage points. Some plants may sell the phospholipids as crude lecithin. 

Mukhopadhyay M, Singh S. Refining of crude lecithin using dense carbon dioxide as antisolvent. Accepted for publication in J Supercrit Fluids 2003. 

The new process involves the production of de-oiled lecithin by subjecting crude lecithin to supercritical CO2 extraction. The soy bean oil dissolves in CO2 and lecithin does not. One of the examples relates that 1,000 g of cmde lecithin is extracted with CO2 at 60 °C and 400 aun for 4 hours. The CO2 extracts 380 g of a yellow, clear oil, 30 g of water, and the residual material, 580 g of a solid, light yellow substance, which is the deoiled lecithin, is removed from the extraction vessel at the end of the cycle. 

PC, a major class of phospholipids which are important components of the membrane lipids in animals and plants. They are zwitterionic and contain, in bound form, glycerol, phosphoric acid, fatty acids (2 moles) and choline. A major component of crude lecithin from soybean and other vegetable oils. 

This processing step is of special importance for rapeseed and soybean oils. Water (2-3%) is added to crude oil, thereby enriching the phospholipids in the oil/water interface. The emulsion thus formed is heated up to 80 °C and then separated or clarified by centrifugation. The crude lecithin (cf. 3.4.1.1) is isolated from... 

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